Clippings by retiredprof

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RE: What are ramps? (Follow-Up #7)

posted by: walkerjks on 04.27.2009 at 09:29 pm in Vegetable Gardening Forum

Ramps can definitely be cultivated. As far as I know, this is the only commercial producer of ramps:

But you can definitely grow a patch yourself under the right conditions or simply buy in season.

Here is a link that might be useful: Commercial ramps


clipped on: 04.29.2009 at 08:28 am    last updated on: 04.29.2009 at 08:28 am

RE: What are ramps? (Follow-Up #5)

posted by: jimster on 04.27.2009 at 05:00 pm in Vegetable Gardening Forum

Where I am from, in Western New York near the Pennsylvania border, ramps are know as leeks. Wild leeks are nothing like garden leeks except that both are alliums. They grow in wooded areas where the soil has lots of leaf mold. At this time of year, leek dinners are put on by rod and gun clubs and other organizations. They are indeed pungent and odiferous. Leek breath can be overwhelming. When I was in grade school, the teacher banned one leek eater to the hallway because nobody could stand to have him in the classroom.

A few years ago, when I found a large, dense patch of leeks, I transplanted a bunch of them to a shady area at the rear of my city property where the soil is humusy and fairly moist. The leeks have thrived there although they have not multiplied enough for a good harvest.

The article linked below has a nice photo of a mess of leeks.


Here is a link that might be useful: Ramps (Wild Leeks)


clipped on: 04.29.2009 at 08:27 am    last updated on: 04.29.2009 at 08:27 am

RE: Hoophouse Question (Follow-Up #39)

posted by: kiddo_1 on 04.23.2009 at 06:59 am in Winter Sowing Forum

Hey monipsych.
I paid about $9.00 for the hardware:
2 10-foot 1/2" pvc tubes (cut in half to 5' length) @ $2.77/ea (Lowe's plumbing dept)
16 1/2" plastic clamps (they were 5 @ $.68) (same dept as tubes)
32 1/2" screws to attach the clamps to the planks (I had them)
8 2" screws to screw the frame together (I had them)
1 2-mil 9x12' plastic 'drop cloth' @ $3.50 (paint dept)
4 spring clamps (at Marc's - cheapies - 2 @ $.99) (or were $.99/ea in Home Depot hardware dept - Lowe's were too pricey).

I already had:
Bifold door, exterior semi-gloss paint to seal the door against the moisture, the cedar planks, all the screws and the sawhorses.

At the end of the season I'll just unscrew the frame, remove the hoops, then just store away until next year.

It took me 30 minutes to assemble. In fact, I'm making another one today to cover my WS annuals.

You're in zone 6. Will you be having frost/freezes yet this year? I'm in zone 5 and it been freezing some nights. In fact frosted last night. And even though the next 6 days will be warm and above freezing at night, I'll be keeping mine up till after mid-May because here in NE OH we still get some frosts until then.

This is a simple anyone-can-do project - after all - I did it!

And if you need even more encouragement - Prof might build one *snark* ;-D

Good luck.


clipped on: 04.23.2009 at 04:10 pm    last updated on: 04.23.2009 at 04:10 pm

RE: Hoophouse Question (Follow-Up #34)

posted by: kiddo_1 on 04.21.2009 at 06:38 pm in Winter Sowing Forum

Hi prof. My bifold doors are 36" wide and 79" long. I made the frame 67.5" by 32" (outside measurement). The frame could have been made another 11" long and still fit on the door, but I wanted to leave a 'shelf' at the end where I can set my coffee cup, clippers, gloves, wine glass, etc. The hoops are 1/2" pvc cut to 5' length. Does that do it for ya?


clipped on: 04.23.2009 at 04:10 pm    last updated on: 04.23.2009 at 04:10 pm

RE: Hoophouse Question (Follow-Up #32)

posted by: kiddo_1 on 04.21.2009 at 06:55 am in Winter Sowing Forum

mnwsgal - for my table top hoop house, I bought 1/2" pvc in 10' length and cut them in half. When 'hooped' they are a nice height (about 20-22") in the middle. Find a piece of wire and play with it in your cedar box and see how high you want your hoops to be, allow some headroom for your plants. Then just measure the length and go from there. Tip - my 5' long 1/2" pvc would not bend well if my cedar frame had been any narrower. If you have a smaller box, try to find 3/8" pvc. Made wonderful hoops for floating row cover over 18" wide rows in the garden, but they don't sell that diameter here anymore. :-(


clipped on: 04.23.2009 at 04:09 pm    last updated on: 04.23.2009 at 04:09 pm

Hoophouse Question

posted by: retiredprof on 04.02.2009 at 03:18 pm in Winter Sowing Forum

Well, I made the hoophouse over one of the raised beds, potted-up the toms into 16-oz cups and moved them in there. I found some 6ml plastic sheeting (same opacity as a milk jug) that fits over the whole bed just great, with enough extra around the bottom sides to be held down with bricks.

Now for the question: Do I need to cut ventilation holes in the plastic? I plan to open the cover every day and close it up at night.



clipped on: 04.23.2009 at 04:08 pm    last updated on: 04.23.2009 at 04:08 pm

PVC photos for Tom

posted by: nancysil on 07.20.2006 at 10:03 pm in Growing Tomatoes Forum

Photobucket - Video and Image Hosting

Photobucket - Video and Image Hosting

Photobucket - Video and Image Hosting


clipped on: 04.23.2009 at 06:14 am    last updated on: 04.23.2009 at 06:14 am

RE: when to cut down asparagus ferns? (Follow-Up #1)

posted by: digdirt on 11.09.2008 at 01:25 pm in Vegetable Gardening Forum

When they turn brown and die as that is the sign that the crowns have gone dormant as needed. In our zone that is usually sometime in January. If you cut them while still green the crowns are just stimulated to produce more new growth - not good.



clipped on: 03.21.2009 at 10:36 am    last updated on: 03.21.2009 at 10:36 am

when to cut down asparagus ferns?

posted by: thomis on 11.09.2008 at 12:33 pm in Vegetable Gardening Forum

When should you cut down the asparagus ferns? I have heard that they should be left alone until they die and then cut, removed, and burned to kill any asparagus beetles. But its November 9 and they are mostly still green. Any advice is appreciated, many thanks!



clipped on: 03.21.2009 at 10:36 am    last updated on: 03.21.2009 at 10:36 am

RE: Asparagus aspirations (Follow-Up #2)

posted by: ShenValleyJoe on 04.18.2005 at 05:58 am in Square Foot Gardening Forum

I went with the Jersey Knight Hybrid, because you can harvest a little the second year. When they go to fern they will be 2-4 feet high, so make sure that they won't shade your other plants. 12-18 inch spacing is recommended. Toss in some triple phosphate when you plant.

Here is a link that might be useful: Jersey Knight Asparagus


clipped on: 03.21.2009 at 10:33 am    last updated on: 03.21.2009 at 10:33 am

Shallow trench planting for stronger plants thicker spears (Follow-Up #3)

posted by: stephen_albert on 01.10.2009 at 11:05 pm in Vegetable Gardening Forum

Asparagus crowns can be planted up to 8 inches deep. Why? Deeper planting will result in fewer but larger, disease-free spears. Use the staggered spacing described by Dave above, but also: for each staggered row make a trench about 12 inches wide and 8 inches deep. Mound up soil in the bottom of the trench--use loose, manure-enriched soil--this mound will be about 3 inches high. Spread the claw-like asparagus roots gently on the mound, spaced 12 to 15 inches apart. Then cover the crowns with 2 inches of light soil. When the shoots emerge later in spring gradually over the season fill in the remainder of the trench with soil--never fully cover the growing tips. Continue until the end of the season when the trench is filled, then cut off the foliage. Next year--first limited harvest year--you will begin to reap the benefits of this method: stronger plants, thicker spears.

Here is a link that might be useful:


clipped on: 03.21.2009 at 10:27 am    last updated on: 03.21.2009 at 10:28 am

RE: Help me with spacing for asparagus in a raised bed (Follow-Up #1)

posted by: digdirt on 01.10.2009 at 09:24 pm in Vegetable Gardening Forum

You could do 2 rows 25' long with the plants 10-12" apart but no closer. 3 rows on 3' wide bed would be too crowded. Stagger the 2 rows of plants.

X - X - X - X

- X - X - X

Assuming adequate feeding and all the crown head will rapidly expand to fill that 10-12 inches within 5 years. And the massive root system will fill the bed in about that same time so over-planting/over-crowding needs to be avoided to avoid die-off.

Link below shows a guys hand holding what looks to be a 2 year old crown. Just scroll down the page a bit.


Here is a link that might be useful: Asparagus


clipped on: 03.21.2009 at 10:26 am    last updated on: 03.21.2009 at 10:26 am

Help me with spacing for asparagus in a raised bed

posted by: bigoledude on 01.10.2009 at 05:40 pm in Vegetable Gardening Forum

The raised bed I'm preparing for my asparagus is 3 feet wide and about 25 feet long. How should I space them?

Is it OK to plant 3 plants across for the entire 25 feet length?

The literature from our county agent gives information for row planting only. They say to plant them 12 inches apart on the row and, space the rows 3 feet apart.

It's sorta embarrassing to admit but, I've gardened seriously for 35 years and, never even seen an asparagus plant! Ray


clipped on: 03.21.2009 at 10:26 am    last updated on: 03.21.2009 at 10:26 am

RE: Earliest planting of peas (Follow-Up #10)

posted by: steve22802 on 03.02.2009 at 10:35 pm in Vegetable Gardening Forum

I've been experimenting with pre-sprouting peas this year too. First I put the peas in a plastic container and then fill the container with warm water. I let the peas soak for about 12 hours. During this time they absorb lots of water and come out of dormancy. Then I drain off all the water and cover the container with plastic that has a few small holes poked in it. This allows some transpiration but keeps the seeds from drying out too fast. (I have a wood stove in my house so my humidity is very low and everything dries out rapidly.) Next I place the container somewhere warm. (In the room with the wood stove for me.) Given these conditions the seeds will visibly start to sprout in as little as 24 hours and can then be planted outside in the soil. If you need to hold them for several days just rinse and drain them twice a day to keep them hydrated. The following picture, taken 48 hours after the 12 hour soak, shows some peas I am presprouting.


The next pictures show some leftover peas from a batch I started pre-sprouting on February 8th. (22 days ago) I planted most of this first batch on February 15th but once my raised bed was full I still had these left over. I still haven't gotten around to planting them but they look pretty healthy and are about to unfurl their first leaves. I think I'll plant them on Wednesday, after the current cold spell breaks, and treat them like seedling transplants (plant with leaves above ground) rather than mere pre-sprouted seeds.



I never intended to sprout these leftovers for so long out of the soil but now that I have I kind of like the idea. It's kind of like raising seedlings for transplants but without all the mess of soil and pots. I keep rinsing them every day with tap water and they just keep growing apparently satisfied for now with the nutrients remaining in the seed. What do you think of that?


clipped on: 03.09.2009 at 06:32 pm    last updated on: 03.09.2009 at 06:32 pm

RE: Sowing dill to protect my Dahlias. (Follow-Up #1)

posted by: littleonefb on 03.05.2009 at 01:16 am in Winter Sowing Forum

I've never heard of dill being used to repel any insects, but I do know that nasturtium will help keep away cucumber beetles away.

Here's a list of companion plants and plants that help to repel insects from
Countrybrook Farms Nursery & Garden Center in New Hampshire


Allium ~ repels aphids, carrot flies, moles, tree borers, weevils, companions with almost all vegetables *dislikes beans, peas
Angelica ~ attracts beneficial lacewings, ladybugs & papasitic wasps *dislikes being near dill
Anise ~ repel aphids cabbageworm, attracts beneficial wasps, companions with coriander, *dislikes carrot
Apple ~ companions with chive *dislikes being near black walnut, hawthorn
Asparagus ~ companions with basil, carrot, parsley, tomato
Basil ~ repel flies, mosquitoes, tomato hornworm, asparagus beetles, companions with asparagus, beans, broccoli, Brussels sprouts, cabbage, cauliflower, collard, kale, marigold, parsley, pepper, tomato, *dislikes rue
Bay Leaves ~ plant containers and bring in the house for preventing invasions of ladybugs in fall
Beans ~ companions with basil, borage, broccoli, cabbage, carrot, celery, corn, collard, cucumber, eggplant, potato, larkspur, lettuce, marigold, mint, peas, radish, rosemary, savory, strawberry, sunflower, tansy *dislikes beet, chive, garlic, onion, pepper
Bee Balm ~ attracts beneficial insects, improves growth and flavor of tomatoes
Beets ~ companions with cabbage, onion, lettuce, sage
Borage ~ repels tomato worms, attracts honeybees, adds calcium and potassium to the soil, companions with beans, squash, strawberry, tomato, fruit trees
Blackberry ~ companions with tansy
Broccoli ~ companions with basil, beans, cucumber, dill, garlic, hyssop, marigold, mint, nasturtium, onion, potato, radish, rosemary, sage, thyme, tomato, *dislikes grapes, lettuce, rue
Cabbage ~ companions with all strong scented herbs, basil, beets, beans, chamomile, celery, chard, dill, garlic, hyssop, larkspur, lettuce, marigold, mint, nasturtium, onion, rosemary, sage, spinach, thyme, tomato *dislikes being near strawberry, grapes, rue
Caraway ~ attracts beneficial insects, can be planted all throughout the garden to loosen soil *dislikes carrot, dill
Carrot ~ companions with beans, chive, delphinium, pea, lettuce, pepper, radish, rosemary, onion, sage, tomato *dislikes caraway, dill
Catmint ~ attracts beneficial insects, companions with eggplant, repels flea beetles, squash bugs, cucumber beetles
Cauliflower ~ companions with basil, bean, garlic, hyssop, lettuce, marigold, mint, onion, rosemary, sage, thyme *dislikes growing near grapes, rue
Celery ~ repels white cabbage flies, companions with beans, cabbage, leek, nasturtium, onion, spinach, tomato,
Chive ~ companions with carrot, fruit trees, grapes, potato, rose *dislikes beans, peas
Coriander ~ companions with anise, potato, repels aphids, attracts beneficial insects *dislikes bean, peas
Chamomile ~ companions with cabbage, cucumber, onion, improves flavor
Collard ~ companions with basil, bean, cucumber, dill, garlic, hyssop, lettuce, marigold, mint, nasturtium, onion, potato, radish, rosemary, sage, thyme *dislikes grapes, rue, tansy
Corn ~ companions with beans, cucumber, dill, pea, potato, melon, pumpkin, squash, sunflower
Cucumber ~ companions with beans, broccoli, cabbage, carrot, cauliflower, chamomile, collard, corn, kale, lettuce, marigold, nasturtium, onion, peas, radish, savory, sunflowers, tomato *dislikes all aromatic herbs, potato, sage
Delphinium (larkspur) ~ companions with beans, cabbage, oats *dislikes carrot, chard, parsnip, turnip
Dill ~ attracts beneficial insects most especially predators of aphids, companions with broccoli, cabbage, collard, cauliflower, lettuce, onion, improves flavor of cabbage *dislikes angelica, caraway, carrot, lavender, tomato
Eggplant ~ companions with beans, garlic, marigold, peas, spinach, tarragon, thyme *dislikes apricot
Fennel ~ companions with basil, dill *dislikes bean, coriander, pepper, tomato
Garlic ~ companions with most vegetables especially collard, raspberry, rose, repels aphids, beetles, weevil, borer, spider mites *dislikes beans, peas
Geranium ~ repels cabbage worm, Japanese beetles, companions with cabbage, corn, grapes, roses
Grapes ~ companions with horseradish *dislikes beans, cabbage, Brussels sprouts, broccoli, cauliflower, chives collard, kale, radish, peas, blackberry, peach
Horseradish ~ companions with potato
Hyssop ~ companions with broccoli, Brussels sprouts, cabbage, cauliflower, collard, grape, kale *dislikes radish
Kale ~ companions with basil, beans, dill, garlic, hyssop, lettuce marigold, mint, onion, radish rosemary, sage, thyme, tomato * dislikes grapes, rue
Leek ~ companions with carrot, celery, onion, repels carrot flies
Lettuce ~ companions with beans, carrot, cauliflower, chrysanthemum, collard, cucumber, onion, radish, strawberry *dislikes broccoli, barley, fava bean, rye, wheat
Marjoram ~ companions with pepper, sage
Marigold ~ many insects are confused or repelled by the smell, like the Mexican bean beetle and harmful soil nematodes and Colorado potato beetles, companions with most vegetables especially beans, broccoli, cabbage, kale, pepper, rose, strawberry, tomato, use freely throughout vegetable garden
Melons ~ companions with corn, nasturtium, radish
Mint ~ improves flavor, repels many insects, do not plant directly into garden, this is perennial and invasive, plant in containers and place near companions with beans, broccoli, cabbage, cauliflower, cabbage, collards, tomato,
Mustard ~ use as a trap crop to attract pest insects away from other plants, pick and destroy the harmful insects, attracts beneficial predator insects, companions with Brussels sprouts, cabbage, cauliflower, radish, turnips
Nasturtium ~ repels aphids, cucumber beetles, squash bugs, white flies, borers, companions with beans, broccoli, cabbage, collard, cucumber, radish, squash, fruit trees
Onion ~ repels cabbage moth, aphids, weevils, carrot flies, spider mites, moles and some nematodes in soil, companions with beets, broccoli, Brussels Sprouts, cabbage, carrot, cauliflower, celery, chamomile, collard, cucumber, dill, kale, lettuce, pepper, potato, radish, rose, savory, squash, strawberry, tomato *dislikes beans, peas, rue, sage
Oregano ~ companions with broccoli, cabbage, pepper
Parsley ~ repels carrot flies, asparagus beetles, companions with asparagus, carrot, tomato, rose
Parsnip ~ *dislikes delphinium
Peas ~ provides extra nitrogen into the soil especially with corn, companions with beans, carrots, chives, corn, cucumber, eggplant, lettuce, radish, spinach, tomato, turnip *dislikes black walnut tree, chives, garlic, grapes, onion, gladiola, potato
Peach ~ companions with grape, garlic, onion, asparagus * dislikes potato, tomato, raspberry
Pennyroyal ~ repel ants, aphids, ticks, fleas, cabbage maggot, companions with broccoli, Brussels sprouts, cabbage
Pepper ~ companions with beans, carrot, fennel, horehound, marigold, marjoram, onion, tansy *dislikes black walnut tree
Petunia ~ companions with beans, potato *dislikes apricot trees
Plum ~ *dislikes apricot trees
Potato ~ companions with beans, broccoli, cabbage, cauliflower, cabbage, collard, coriander, dead nettle, horehound, horseradish, lettuce, marigold, onion, petunia, squash, sunflower, tansy *dislikes apple, apricot, black walnut, pear
Radish ~ repels cucumber beetles, companions with beans, broccoli, cabbage, carrot, cauliflower, chervil, collard, cucumber, grapes, lettuce, melon, onion, peas, squash *dislikes hyssop
Raspberry ~ companions with tansy
Rose ~ companions with chive, feverfew, garlic, geranium, marigold, onion, parsley
Rosemary ~ repels cabbage moth, beetles, mosquitoes, slugs, companions with beans broccoli, cabbage, carrot, cauliflower, collard, sage
Rue ~ repels Japanese beetle, companions with broccoli, rose, raspberry *dislikes basil, cabbage, cauliflower, sage
Sage ~ repels cabbage moth, carrot flies, ticks, companions with broccoli, cabbage, carrot, cauliflower, collards, marjoram, rosemary, strawberry *dislikes onion, rue
Savory ~ improves growth and deters bean beetles, companions with beans, onions
Soybeans ~ repels chinch bug, Japanese beetles, adds nitrogen to soil companion with corn
Spinach ~ companions with celery, cauliflower, eggplant, peas, strawberry
Squash ~ companions with beans, corn, mint, nasturtium, onion, radish, sunflower, tansy *dislikes potato
Strawberry ~ companions with borage, beans, lettuce, onion, sage, spinach *dislikes cabbage
Sunflower ~ attracts beneficial lacewings and parasitic wasps, companions with beans, corn, squash *dislikes potato
Tansy ~ repels ants, cucumber beetle, flies, Japanese beetle, squash bugs, peach aphids, colorado potato beetles, companions with blackberry, cucumber, fruit trees, grapes, pepper, raspberry, rose *dislikes collard
Tarragon ~ is reported to enhance most vegetables
Thyme ~ repels cabbage worm, flea beetles, cabbage maggot, companions with broccoli, cabbage, cauliflower, collard
Tomato ~ companions with borage, broccoli, cabbage, carrot, cauliflower, celery, chive, horehound, marigold, onion, parsley, peas, petunia, mint, sage *dislikes apricot, dill, black walnut, corn, fennel
Turnip ~ *dislikes delphinium, mustard


clipped on: 03.05.2009 at 10:30 am    last updated on: 03.05.2009 at 10:30 am

Do you use Tom Clothier's Database?

posted by: seedmama on 03.03.2009 at 04:20 pm in Winter Sowing Forum

I do, especially this time of year. One of the most common questions in the peak of WS season is whether to plant something "now". The question usually has "too late" or "too early" as part of the subtext. The database lists ideal temperature for germination and how long it should take to germinate at that temp. It also indicates whether a seed needs to be exposed to cold, ie cold stratification and for how long. I use the database as a thumbnail gauge for how early or late something should be planted.

As an example, I was received some hosta seeds in the mail today. I've never sown hosta, so I went to Tom Clothier and looked them up.

It said "Hosta elata, minor, montana, sieboldiana, and ventricosa , Sow at 20�C (68�F), if no germination in 3-4 wks, move to -4 to +4�C (24-39�F) for 2-4 wks, recycle".

First that tells me they aren't frost tender and don't need to be held until later. Second it tells me that a little cold strat won't hurt, and may help. In other words, it's not too late, but I don't want to wait until the temps here warm up to the mid 80s.

I use the database extensively in the late fall. I take my seeds out of alphbetical order and put them in order by sowing date, with the sowing date corresponding to typical temperatures in my region. I use tabs with ranges of half months (Dec 16-30, January 1-15, etc.) If something needs four months at 24-39 degrees, it would be sown first. Something that needs two weeks at 40 degrees would be sown later in the cold season but not last, and so on. I do this because of the volume of containers I plant. It's not realistic to think I can have everything sown by the end of January. I don't want to come across seeds at the end of the alphabet in mid May only to discover they needed two months of cold to germinate, or would have had peak germination at 50 degrees.

One thing not to do when using the database is to try to mimick the listing exactly. It was designed for greenhouse growers who want to cut to the chase instead of letting mother nature do the work for them. As a winter sower it is best used as a general guideline for determining too early or too late.

Hope this helps someone.

Here is a link that might be useful: Tom Clothier's database


clipped on: 03.03.2009 at 04:55 pm    last updated on: 03.03.2009 at 04:55 pm

RE: Teeny Weeny Eggplant!!! (Follow-Up #10)

posted by: jll0306 on 10.21.2008 at 02:37 am in Vegetable Gardening Forum

I think yours are Bambinos. i found them and Calliope, another miniature brand described at

Bambino Hybrid
This 52 day hybrid goes to about 12"tall and yields masses of 1 1/2" diameter round eggplant. Great for frying, cooking, and pickling. Recommended Container Size: you can grow 3 to 4 plants in a 10 gallon container. Or at least a 10" pot.

Calliope Hybrid:
Calliope will yield lots of small eggplants even under challenging conditions (cool climates) - making it an excellent choice for northern gardeners. The eggplants are tear-drop shaped and are violet streaked with white and very pretty indeed. Pick them when 2" in diameter for baby eggplants, 4" in diameter for mature eggplants.


clipped on: 02.18.2009 at 11:11 am    last updated on: 02.18.2009 at 11:11 am

RE: Vegetables in partial shade? (Follow-Up #7)

posted by: ekgrows on 02.05.2009 at 10:34 am in Vegetable Gardening Forum

My go-to garden book lists these plants that tolerate partial shade: Arugula, basil, bee balm, beets, broccoli, chard, cabbage, carrots, chervil, cucumbers, endive, kohlrabi, lettuce, lovage, mint, peas, parsley, parsnips, radish, rhubarb, and spinach.
I personally have had luck growing broccoli, radishes, carrots, beets and peas in a bed that gets sun until noon. Cucumbers have done just okay.


clipped on: 02.05.2009 at 06:02 pm    last updated on: 02.05.2009 at 06:03 pm

Photoperiods and growing

posted by: wordwiz on 01.19.2009 at 04:54 pm in Growing under Lights Forum

I found an abstract and then someone else found the complete report. Here is an excerpt from it. It deals with tomatoes and sweet peppers but should also apply to hot peppers.

For tomato, best growth and yield were obtained under a photoperiod of 14 hours (Vzina et al., 1991; Demers et al., 1998b). Photoperiods longer than 14 h did not further increase yield. Photoperiods of 20 and 24 h can even decrease yield and caused leaf chlorosis (after 6 to 8 weeks) (Vzina et al., 1991; Demers et al., 1998b). Although long term use of a 17-h photoperiod does not increase growth and yield compared to 14 h, it might be interesting to extend the photoperiod to 17 h in order to increase total light provided to plants especially during the months with the lowest natural light levels (December-January). However, if a 17-h photoperiod is used, it is important that the dark period be uninterrupted, since splitting the dark period of 7 h in two short nights of 3.5 h (separated by a light period of 4 h) caused leaf chlorosis and decreased growth and yield (Vzina et al., 1991).

For sweet pepper, a 20 h-photoperiod was optimal for plant growth and productivity (Demers et al., 1998a). Yield under continuous light (24-h photoperiod) was equivalent to yield under photoperiods of 15 or 16 h (Costes et al., 1970; Demers et al., 1998a). Extension of the photoperiod from 15 or 16 h to 24 h decreased the average size of pepper fruits (Costes et al., 1970; Demers et al., 1998a).

Continuous light caused some leaf deformities (wrinkles) but no chlorosis in sweet pepper grown in greenhouses. Although long term use of continuous light is detrimental to tomato and pepper plants, tomato and sweet pepper plants can take advantage of the extra light energy provided by continuous lighting for a short period of time. Early vegetative growth and fruit production of tomato and pepper plants were generally improved under continuous light compared the 14-h photoperiod (Demers et al., 1998a, 1998b). However, after that initial period, plants under continuous light grew more slowly than plants exposed to 14-h photoperiod; so that tomato and pepper plant growth and yield under 14-h photoperiod were then equal to or higher than under continuous light at the end of the experiment.

Costes et al. (1970) also observed that continuous light improved the early performance (hastening of flowering and fruit set, increased early yield) of sweet pepper plants compared to a 15-h photoperiod. Therefore, it might be possible to use continuous light for a short period of time (5 to 7 weeks) to improve growth of tomato and sweet pepper, especially during the months with the lowest natural light levels (December and January). However, such a practice should be investigated in order to determine if short term use of continuous light might have residual negative effects on tomato and sweet pepper plants.

Tomato and sweet pepper plants do not take advantage (no increase in yield) when grown under photoperiods longer than 14 h (tomato) or 20 h (pepper). Tomato plants, but not sweet pepper, develop leaf chlorosis under continuous light. In the next sections, we will examine the role of the carbon metabolism, pigments, light spectral quality and day/night temperature differential in the development of these negative effects of long photoperiods.

Carbon Metabolism
High starch and soluble sugar accumulations were observed in leaves of tomato plants grown under long photoperiods, and it was suggested that these accumulations could be related to the development of the leaf chlorosis (Bradley et al., 1985; Logendra et al., 1990; Dorais, 1992).

Studies on other species support the hypothesis of a relationship between leaf chlorosis development and starch and sugar accumulations. For example, continuous light caused increased leaf starch and hexose accumulations and leaf chlorosis of eggplants (Solanum melongena L.) (Murage et al., 1996). However, eggplants growing under continuous light but in a CO2-free atmosphere for 12 h per day accumulated less starch and hexoses, and did not develop leaf chlorosis.

Exposure of tomato and sweet pepper plants to continuous light resulted in increased foliar contents in starch in tomato and sweet pepper, in hexoses (glucose and fructose) in tomato and sucrose in sweet pepper (Dorais et al., 1996; Demers et al., 1998a, 1998b). However, the reduction of the number of fruits on the plants did not modify the pattern of accumulation of starch and sugars in leaves of tomato and sweet pepper plants exposed to photoperiods of 14 and 24 h (Demers et al., 1998a, 1998b). Moreover, the reduction of the number of fruits on the plants did not influence the severity nor the date of appearance of the foliar chlorosis in tomato plants grown under continuous light. This indicates that accumulations of starch and soluble sugars are not caused by a limiting sink capacity. If there is a relationship between the excessive starch and soluble sugar accumulations and the development of the negative effects (leaf chlorosis, decreased growth and productivity) of the long photoperiods on tomato and sweet pepper, it is most likely a limitation of the carbon metabolism at the leaf level which is responsible for these accumulations.

In tomato, the use of continuous light caused, in addition to the foliar chlorosis and increased foliar contents in starch and hexoses, a reduction of the photosynthesis rate and of the activity of the sucrose phosphate synthase (SPS) enzyme (Demers, 1998). These reductions in photosynthesis and of SPS activity occurred between 6th and 8th week
under continuous light, i.e. about at the same time as the foliar chlorosis appeared, while starch and hexoses contents in leaves increased during the first 4 weeks of the experiment.

Since the reduction of the SPS activity occurred after the increase in starch and hexoses, it is thus impossible that the reduction of the SPS activity is responsible for these accumulations. However, it is possible that the SPS activity in vivo is limiting, which would explain the hexose increase. This suggests the limiting step of the export of photosynthates is the synthesis of sucrose in tomato and would explain the absence of growth and the productivity increase under continuous light. Furthermore, the increased hexose levels in the cytoplasm, by a feedback effect, would limit the export of the triosephosphate (photosynthesis products) out of the chloroplast, which would then be redirected towards starch synthesis, thus explaining the increased starch contents.

Moreover, the increased accumulation of starch would generate, by a feedback effect, an overload of the Calvin cycle, which would gradually cause the observed decrease of the CO2 fixation rate. Are the starch accumulations responsible for the leaf chlorosis in tomato? It is possible that the overload imposed on the Calvin cycle (decreased photosynthesis) could limit the use of the reducing potential (ATP, NADPH) produced by the luminous phase of photosynthesis, thus causing an overload on the electron transport chain and the photo-oxidation of the chlorophylls (decrease in the leaf chlorophyll contents), and thus explaining the observed leaf foliar chlorosis. Transgenic tomato plants (in which a gene coding for the SPS enzyme was incorporated and overexpress this enzyme) could be used in future studies to test if accumulations of starch in leaves are responsible for the development of chlorosis observed in tomato plants exposed to continuous light. Transgenic tomato plants (overexpressing SPS) have higher photosynthesis rates and accumulate less starch and more sucrose than non-transformed
plants, especially under conditions of saturating light and CO2 (Galtier et al., 1993, 1995; Micallef et al., 1995). One can put forth the assumption that, under continuous light, leaf starch contents would be lower in transgenic plants than in normal plants. If this is the case, the reduction of the leaf starch content in transgenic plants should thus prevent the development of the leaf chlorosis, or at least decrease its severity.

In sweet pepper, the use of continuous light caused an increase in the leaf starch and sucrose contents, but did not affect leaf hexose contents, photosynthesis rates and SPS activity (Demers, 1998). The increased foliar contents in sucrose indicate that SPS activity in sweet pepper is not limiting as in tomato. Increased accumulation of starch in
sweet pepper plants exposed to continuous light would be explained by the fact that continuous light results in a longer period of time over which starch synthesis occur, but without overloading the starch synthesis pathway. Thus, starch accumulation in sweet pepper under continuous light would not be important enough to cause a reduction in CO2 fixation (no overload of the Calvin cycle). Increased leaf contents in sucrose suggest that sucrose export would be possibly limiting. In sweet pepper plants, the export rate of carbon (as sucrose) out of the leaf is constant, and the export rate would be limited at the level of the loading of sucrose in the phloem (Grange, 1985, 1987). This would explain why the growth and the productivity of the sweet pepper plants do not increase under continuous light.

In growth chambers, continuous light caused leaf chlorosis, decreased photosynthesis rates, and reductions in leaf contents in pigments (chlorophyll a and b,
carotene, xanthophylls) in both tomato and sweet pepper plants (Demers, 1998). Leaf chlorosis, decreased photosynthesis rates and loss of pigments were more important and occurred earlier in tomato plants than in sweet pepper. Compared to sweet pepper plants, EPS ratio (epoxidation state of the pigments of the xanthophyll cycle) was lower in tomato, indicating a greater need for energy dissipation and a more important state of stress (caused by excessive light). Pigments such as carotene and xanthophylls (violaxanthin, antheraxanthin, zeaxanthin) play a significant role in the protection of the photosynthetic apparatus against damage that could be caused by an excess of light.

Carotene and xanthophyll levels were higher in sweet pepper plants than in tomato. Thus, sweet pepper has a better protection against the degradation of chlorophylls, which would explain why leaf chlorosis appeared later and were less severe in sweet pepper.

Longer periods of light are not better, at least after a point!



clipped on: 01.27.2009 at 12:45 pm    last updated on: 01.27.2009 at 12:46 pm