Polycarbonate Green House,How Long Can It Extend Growing Season,Zone 6

6 years ago

I am attracted to a $600 polycarbonate green house, 6x8, from Costco.

https://www.costco.com/Harmony-6'-x-8'-Greenhouse-with-Starter-Kit.product.100032497.html

Since the winter in Boston area can be very long and extremely brutal, I do not intend to heat it and keep growing in the deep winter. The major purpose is to extend the growing season normally between May to October.

It has automatic ventilation window. I assume it will automatically open when temperature raises too high in the noon time. I should not spend too much extra time on taking care of green house itself.

My question is how long it can extend the growing season.

For example, I want to grow flowers like zinnia and cosmos. Usually I plant the seed in April, germinate in Mid May, and blossom in Mid to late July. With a green house, and occasional heating during the cold spell, I guess I can start planting in early March, and move out in Mid May. Will these hardy flowers like zinnia and cosmos bloom in May? What other flowers will significantly benefit from this green house?

I also have a vegetable garden. For cold-tolerant beans and salads, can I plant in February and harvest in May? If I want to harvest beans and salads inside the green house in November and December, when should I plant the seed? For vegetables that I want to grow outside during the summer, like tomato and zucchini, when do I plant, move out, and harvest?

I have been enjoying planting flowers and vegetables since I moved in my house 9 years ago. Green house should open another dimension for me. I would like to know how much benefit it can bring, and timing for the flowers and vegetables that will benefit significantly from the green house.

Featured Answer

defrost49

5 years ago

sorry I didn't see this sooner. I agree, Eliot Coleman's books are great plus you can see his posts on Facebook about what he is doing in his high tunnel. A local market farmers also posts his photos and sells fresh veggies at the winter market here in zone 5B NH. I have a greenhouse plastic covered wood frame high tunnel. The ground never freezes inside but the air temps as mentioned by another poster get just as cold inside as outside when the sun goes down. We have a thermometer in our kitchen with sensors in different places so I know what the temp is in the high tunnel as well as outdoors. There are some easy tricks to keeping things warm like putting Agribon fabric over plants. Some of the market gardeners are using supplemental heat early in the season to get an early start on tomatoes.

Johnny's Selected Seeds website has some good info about high tunnels. Yes, you can plant cold hardy things earlier but you also have to know that there is a Persiphone period during winter when there is not enough sun so plants go dormant.

My simply plastic high tunnel seems capable of being a zone or two warmer depending on how much extra protection I give things. I overwintered rosemary and variegated sages successfully (but not last winter). I'm planting in the ground. Cilantro, kale, claytonia self seed in my high tunnel but not outside. I don't think beans are cold tolerant. Spinach and chard are. I had a goal of picking salad greens for Thanksgiving dinner. I might have done Christmas, too. You will need to read up on varieties because some lettuce is hardier than other varieties. I have had some lettuce start regrowing in early spring.

Surprisingly, even with the sides rolled up and double door open, in summer the temp is easily 100 degrees on sunny days. In winter there can be a huge temperature difference. I have a yard hydrant so I can have water in winter but that requires an underground pipe from the house. My tomato plants are healthier than those growing outdoors.

I still start seed indoors under lights. Between Johnny's and Eliot Coleman's books you can figure when to plant seeds outdoors under plastic to provide fall and winter harvests. I did not do winter crops this past winter because voles and other furry creatures had caused too much damage. Went to undercover a late crop of broccoli only to find every head gone. Also be aware that it gets too hot to be working under plastic in the summer and even some spring days if you don't get out early.

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Comments (7)

NHBabs z4b-5a NH
6 years ago
There are two comments on this model in the Greenhouses and Garden Structures forum. Here's a link that will take you to both:

https://www.gardenweb.com/gardenweb/query/Palram-harmony/topic=strucs

Your link doesn't mention wall thickness, but one of the comments I linked does. Single wall thickness (rather than a double wall which traps an insulating layer of air) won't provide much heat holding capacity, and depending on the tightness of the seals around the panels, you may find that early morning temperatures aren't too different from outside. I don't have any experience with this model, but I think anything less than double walls in New England won't give you too much of a jump start. Just my opinion as someone who at a couple points in the now rather distant past has worked with home built, unheated greenhouses.

You could ask on that forum to see if there is any other feedback.

http://forums.gardenweb.com/forums/strucs

one woman who posts here, Defrost has a home built greenhouse that I think is single layered, and she may have found it worthwhile, so you can search for "greenhouse" on this forum.
mad_gallica (z5 Eastern NY)
6 years ago
For seed starting, basement light setups are usually more cost effective than greenhouses since you don't have to add heating. Normal fluorescents work well, so long as they are close to the plants.
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Dong Liu
Original Author
6 years ago
Thanks NHBabs and gallica for the advice.

The $600 green house from Costco is single-wall. So I need to carefully research on how much extension of growing season it can provide.

I will investigate better ways of indoor seed starting. In the past, without any lighting and fan, the mold killed all the seedlings. With more efficient and affordable LED light, I will see if there is working solution in this year.
mad_gallica (z5 Eastern NY)
6 years ago
LEDs don't strike me as a good idea. 48" fluorescents have been the standard for decades, and one of the reasons is the amount of space directly underneath the bulbs. The usual recommendations are that the plants be less than 2" from the bulbs to give them enough light. I don't even know how to setup a LED to properly light a single six-pack.
bill_ri_z6b
6 years ago
There are numerous new types of LED's for plant growing, seed starting, etc. Just do a search online. Amazon offers several types. Even Home Depot offers LED plant bulbs.

As far as the polycarbonate greenhouse, I would strongly suggest against a single wall type. It will lose most of the heat after sunset, so heating would be expensive. If you had a double, or better yet, a triple wall structure, then it might be OK, But I think the others are correct when they say that indoors with a plant light (LED or other) and a small fan for ventilation would be the most cost effective. I had a single wall greenhouse for years, and it was really a burden to heat it, upwards of $200 a month, and that was several years ago. Prices for fuel/electricity have gone up a lot since then.
HighColdDesert
5 years ago
The main thing is, if you can place it south facing without shade in winter, it will stay much warmer than any other position. Eliot Coleman has wonderful books called the Four Season Harvest and The Winter Harvest Handbook. He is growing in Maine, and using unheated greenhouses he can get various vegetables in every month. Some are just very winter hardy things like kale and other leafies, that he gets growing in late summer and then can harvest fresh in the middle of winter.

I have a similar winter temperature to Boston but am much farther south, and in a dry sunny climate. In my unheated solar greenhouse, leafy vegetables and perennial herbs and carrots continue growing all winter. And I can extend the season for other things by at least a month each direction.

Polycarbonate Green House,How Long Can It Extend Growing Season,Zone 6

defrost49

Comments (7)

NHBabs z4b-5a NH

mad_gallica (z5 Eastern NY)

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Polycarbonate Green House,How Long Can It Extend Growing Season,Zone 6

defrost49

Comments (7)

NHBabs z4b-5a NH

mad_gallica (z5 Eastern NY)

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Dong LiuOriginal Author

mad_gallica (z5 Eastern NY)

bill_ri_z6b

HighColdDesert

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Dong Liu
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