When to plant greenhouse tomatoes?

bogydaveApril 1, 2009

I have a single wall, clear poly-carb greenhouse. I have 3- 8 foot long X 16" deep X 18" wide soil boxes with heat tape in the bottoms. I have the soil up to 58 degrees in the boxes but it still gets down in the teens at night & the inside of the walls condensate & form ice. I can cover the soil boxes with clear plastic, keeping the 60 degree or so temperature around the plants thru the night. During the day I get 65 degrees inside & on sunny days I'm getting 75 deg. We now have about 14 hours of daylight & still increasing. I have thoroughly mixed the soil in the boxes, adding perlite with compost. I just watered the boxes today with hot water & plan to let the moisture even out for a couple of days. I can probably hold 60 degrees in the boxes if covered at night.

I know i'm getting "cabin fever" & want to get things growing.

Should I try a couple of plant & risk losing them or be more patient & wait 2 or more weeks?

I plan to uncover them during the day to let them breath & have a small fan running for inside air circulation. If they were to make it, they'd be "hardened off" to the greenhouse & transplant shock over with when growing season arrives. In Alaska tomatoes have to be grown in the greenhouse, well if you want lots of fruit anyway.

Started tomatoes from seed, 7 weeks old, re-potted in 4" pots 1 week ago. 4" tall plants now.

This would be the earliest I've ever planted the geenhouse by about 2 week, but the weather has been cooler this year. Still have snow on the ground.

Heating the greenhouse is out, cost & single wall 8 X 12 greenhouse would take more power than it's wired for. Plus $100 per pound makes tomatoes just a little too spendy.

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jbest123(Zone 5 PA)

Hi bogy, I don't think there are to many people on this forum familiar with AK conditions.


    Bookmark   April 2, 2009 at 3:18PM
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This seems to be working for me. I had tomato sprouts out last night, greenhouse low -0.3C and they look fine.

RE: New greenhouse - what can I do right now with it?

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* Posted by ljpother 3a (My Page) on
Sat, Mar 28, 09 at 19:24

I just put some water in my greenhouse. I realized my rain barrel wouldn't mind being used to hold water :) and I had other containers. I placed a layer of 4l ice cream pails under my flats, which should moderate temperature fluctuations. Altogether, I put about 450 litres of water in. US gallons ~120, imperial ~100. It sounds better in litres. Hopefully, this will be enough to keep the night time temperatures above freezing.

RE: New greenhouse - what can I do right now with it?

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* Posted by ljpother 3a (My Page) on
Tue, Mar 31, 09 at 11:16

The water seems to be having an effect. Lows have been -1,-0.3C,2.3C. Outside temps were -8,-8,-3C. It seems the water is gradually getting warmer and that when the temp tries to go below freezing the heat capacity of the water holds the temperature steady. On the cold nights the green house temp went below freezing about 7AM and stayed there until the sun gets around to the greenhouse, 3-4 hours.

    Bookmark   April 3, 2009 at 4:18PM
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Planted 4 tomatoes in GH with snow still on the ground. Even plant have to be tougher in Alaska.
Tried 5 ways to post pictures, no go .
So much for the easy way. What's the hard way?

    Bookmark   April 3, 2009 at 4:33PM
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Why not just add a small inexpensive electric heater? You can also insulate it with clear bubble wrap inside. You can get it cheap from any packaging house.

    Bookmark   April 5, 2009 at 7:31AM
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Plants looking good so far. Covering the boxes is working well. Cucumber seeds sprouted. Soil temp holding at 70 deg F. :)

Cost prohibitive when getting down in the teens at night still, wire size to gh would have to be larger to supply enough current to run enough heater to keep it above freezing at night.
Take allot of bubble plastic for a 8 X 12 gh to get the "R" value so it would be efficient enough.
I am able to cover the heated soil boxes & keep the plants above 50 deg at night now & when plants get larger if it's still getting cold at night i'll cover them with 5 gallon buckets (jbest's idea). by the time they out grow the buckets, it'll be warm enough during the short nights that not supplemental heat will be needed.
Thanks for the bubble plastic idea, I never though of that one. I can use it for other applications like a dome cover over the heated soil boxes.

    Bookmark   April 6, 2009 at 12:30AM
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Wall-o-waters are 18 tubes 18 inches high of water encircling a plant and can be positioned as a teepee to completely cover the plant in solar-heated water. Your ground heat would also contribute. I have this set-up in a small bed with heat wire underneath and the cucumbers are above the water tubes now. I have wood heat and I check the stove every 3-4 hours in the night and keep it 50-65. It is a 20 foot square wooden pyramid with poly battened on both sides and dirt banked up on the plastic around the bottom. I just built it in February on the frozen ground. Each wall-o-water holds about 3 gallons so if you had say 33 x 3 gallons, you would have a 100 gallon solar heat store. By the time your plants reach the top, it should be less cold at night.

    Bookmark   April 9, 2009 at 8:47AM
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When you plant will likely depend on many things. For what it is worth, we were harvesting tomatoes into December (in Zone 9 - foothills at 2400 feet elevation). In February, I dismantled the raised beds as I was moving them to an area nearer the greenhouse. At that time I took several volunteer plants (Sweet 100) which has sprouted - about 10 or so - and potted them in the greenhouse. I now have a few cherry tomatoes that are ripe - and have harvested some of those - and have many green ones on the plants. The plants are about 4 feet high in the greenhouse, and I have transplanted many more into the new raised beds - those are shorter as I pulled off lower branches and planted deep. I did not have to heat the gh except for 2-3 nights. I also planted kohrabi from seeds and we have been eating that for 2-3 weeks now. Lettuce and chard is also ready. My heirloom seeds are up - some still in the gh and some already in the raised beds, but they are only about 6" high. I have so many tomatoe plants that I will need to build another raised bed. I eventually want to see if I can get tomatoes year round - don't know if I will be able to do so but as it is we seem to have a fairly long season as we ended harvest in December and are getting more now in April - though only a few.

    Bookmark   April 14, 2009 at 4:14PM
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