Greenhouse. How to....

mrscoyleFebruary 22, 2007

OK, so my awesome dad bought me a greenhouse. Not a fancy one - 8x8, plastic covered (opaque, not see thru) and I have no idea what to do now.

Do I start seedlings indoors and them move them to a greenhouse when they are "so" tall?

Do I start the seedlings IN the greenhouse and then move them to the garden (veggie garden)?

Do I need grow lamps?

Do I need heating mats?

When (generally)should we expect our last frost?

This is my very first veggie garden. My toddlers (boys) and I are really excited about it. I don't expect to get everything right this year but I'd like to give it my best shot.

FYI - Yes, I have a very sunny spot for it (protected from wind) on my deck. Yes, the seedlings will be moved to a very sunny spot in my yard.


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maineman(z5a ME)


The plastic covered greenhouses aren't very well insulated, so the temperature inside would be a concern. You might want to put a thermometer in there and see how cold it gets. I probably would add some sort of electric heater that will kick in before the temperature gets down to about 45 °F. And I would probably use the greenhouse as a place to put my indoor-started seedlings when they get too big for their fluorescent lighting. Even partial sunshine is a lot brighter than your fluorescent lights can do.

As to the last frost date, that depends very much on where in Maine you are. Here in the Augusta area, our "safe" no-frost date is Memorial Day.

You could possibly start the seedlings in the greenhouse, using a heating mat and fluorescent lights to lengthen the day. Our days are still pretty short, although they are getting longer. I set the timers on my fluorescent lights for 16 hours of light and 8 hours of dark, although for some plants you might want to vary that. Fluorescents will also help warm your greenhouse a little.

For extra light and heating, I think you are going to need to run an indoor/outdoor extension cord into the greenhouse, preferably at least 12-gauge, and water proof. My seed starting is still exclusively indoors. I also use small electric fans on my seedlings to give them a little artificial breeze to keep them healthy and stocky.

Keep us posted about your greenhouse adventure here in Maine. If it's convenient, you could post some pictures. I plan to build a lean-to greenhouse this year, hopefully sooner rather than later. I have a building permit. Cold weather and large rocks have been hampering my excavation for its foundation.


    Bookmark   February 22, 2007 at 2:51PM
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maineman(z5a ME)


"Do I need grow lamps?

Don't spend a lot of money getting the fancy special purpose grow lamps. The Home Depot Commercial Electric Shoplights, model 732-334, work very well and I have been getting them for about $8 each. They hold two 4-foot bulbs. They can use either the T8 or the T12 fluorescent tubes, but I think the T8 bulbs are a much better choice. I use inexpensive Philips cool white T8 fluorescent bulbs. Home Depot sells them in a "builder's pack" of 10 bulbs for about $19.95, so the bulbs are about $2 each. I have had very good results with these in my indoor growing. It's not at all necessary to mix them with warm white bulbs, which cost more.


    Bookmark   February 22, 2007 at 3:05PM
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Thank you so much for the info. However, I am still unsure of something (please indulge if you answered already and I am just not getting it) ---- can I start my seedlings in the greenhouse? i.e. if sunflowers can be started indoors 2-3 weeks before outdoor planting time, can I start them in the greenhouse in early May? Provided heat and light is sufficient in greenhouse of course. I only press this issue because I REALLY don't have anywhere inside to start the seeds. Can you recommend a good book or a website that might offer more information. I seem to need to read and read and read and read about a project before I start it.

Thanks so much - J

    Bookmark   February 22, 2007 at 4:20PM
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maineman(z5a ME)


Actually, these GardenWeb forums are a pretty good source of information, and you can ask specific questions. The Greenhouses & Garden Structures forum, the Growing from Seed forum, and the Growing under Lights forum would be good places to start.

As for greenhouse books, I have only two. One focuses exclusively on how to build a greenhouse. The other is Ortho's All About Greenhouses. I guess you could say that it is an inexpensive introductory book, but its major coverage areas are

How to choose the greenhouse that's right for you
Plans and instructions for building 10 different styles
State-of-the-art equipment for maximum success
Complete growing techniques for professional-quality plants

I'm sure I will be buying some more books on growing techniques in the greenhouse, but right now I am more focused on the building from a kit. There are a lot of greenhouse books to choose from.


P.S. I don't know if those Amazon URLs will still work, because sometimes URLs expire after a certain amount of time. The iVillage GardenWeb forum URLs should still work.

    Bookmark   February 23, 2007 at 3:14PM
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adirondackgardener(Western Maine)

I would definitely start the seeds in flats indoors if possible, then transplant them to larger pots if necessary and move them to the greenhouse later as outdoor temps rise.

Seeds require more warmth for sprouting than for growing and take up relatively little space at first. There's little sense in heating and maintaining a greenhouse at sprouting temps when a little space in your already heated home can do the trick. Use the greenhouse later as a season extender when the plants begin to take up space (and when temps warm and heating it will not be a big issue.)

And yes, standard shoplight fixtures and the cheap tubes will be adequate for your seedlings.


    Bookmark   February 25, 2007 at 6:48PM
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veilchen(5b southern Maine)

I have a polycarbon-sided greenhouse and actually don't get much use out of it from Nov. to March. I placed a remote thermometer in it the first year so I could see how much heat it retained--it really does warm up during the day, but loses nearly all its heat when the sun goes down. So no, I can't really start any seedlings in there. Unless I hooked up a heater, which would be really expensive.

I have flourescet lights set up in my spare bathroom. Currently I have onion and some perennial seedlings started. By the first of next month I will start tomatoes, peppers, and eggplant. These warm-weather seedlings won't be able to go into the greenhouse until heavy frosts become unlikely (around late April here). My greenhouse does a good job of growing on plants that I started indoors, especially when we get those cold springs and I have to delay transplanting outdoors. My greenhouse also comes in handy in the fall and early winter--I am able to keep greens growing like lettuce and spinach.

By late April through May you could start just about anything from seed directly in the greenhouse, but this doesn't give you enough time to get plants large enough to bloom if you are growing annuals or vegetables. And they may germinate slowly because the nights are cold.

    Bookmark   March 1, 2007 at 7:34AM
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Thank you so much for everything. I guess my problem is this, I am just so EXCITED to give this new a hobby a try. I am a stay at home mom so I am enthusiastic that I will have the time to tackle it. I also have two little boys that I am excited to share this with. Only problem: I have the same kind of patience they do. Maybe this will be a lesson for all of us.

I have found that I like to know what others are doing right now (or any particular time really) re: seed starting, etc... etc....

    Bookmark   March 1, 2007 at 11:07AM
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marthacr(z5 Me)

I have a plastic covered unheated grenouse as well. It is not a place that you want to start seedlings, unless you spend a bit of money on a heater. Some things you could try:
If you have a fridge with space on top, germinate your seeds in flats on top of it. You could start all the seeds a beginner would need in two flats here. You won't need lights till after they sprout. You might even have room on top of your fridge for a small light stand.
Make your greenhouse floor out of some kind of stone or brick to absorb the heat from the sun during the day and hold some for the night. Get either a remote thermometer or a min/max therm. so you can watch the temps for a while BEFORE you put any plants in it.
BTW plants need lower temps to grow than for the seeds to germinate.

In an unheated greenhouse, each layer of covering over a plant changes the climate approx. 1 zone. Start with heating cables, a heat mat or even an old electric blanket. Put your seedlings on this with a plastic tray dome, then put several more "layers" of glass or plactic on this. You can use an old aquarium, a minihoophouse, remay or whatever. Just monitor the temps really really well. With little ones in the house it can be hard to keep up with checking in on your plant babies. It's sort of like 2 AM feedings (at least till the weather straightens out.
Oh, and set the GH up as close to your house as possible. Less travelling for spontaneous checks!

Good luck!

    Bookmark   March 4, 2007 at 1:07PM
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maineman(z5a ME)


"You won't need lights till after they sprout."

Some seeds do need light to help them sprout. Some need total dark. Some need to be covered, some can just set on the surface. You need to check the needs of the particular seeds that you are germinating.


    Bookmark   March 5, 2007 at 9:00PM
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At what temperature should the greenhouse reach before I date put seedlings out there. And about hardening, do I put the seeds out for sunlight hours only? When do I know I can keep them out there day and night? Or do I harden them off in there (daytime only exposure) until they go in the ground. Finally, we do I know I can put them in the ground? When we are safe from frost? End of May?

I would LOVE it if other could post (in all our free time, of couse, ha ha ha) what people are doing and when.


    Bookmark   March 9, 2007 at 10:49AM
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maineman(z5a ME)


"At what temperature should the greenhouse reach before I dare put seedlings out there?"

That depends entirely on what kind of seedlings you are talking about. Some things are cold tolerant and some are very tender and require warmer temperatures.

"And about hardening, do I put the seedlings out there for sunlight hours only? When do I know when I can keep them out there day and night?"

For myself, I don't plan to take plants out in the day and bring them back in during the night, although if you have time to that, it would be a safeguard against the plants getting too cold during the night. I plan to wait until the greenhouse can support the needs of my plants both day and night before I move them out there.

"Finally, when do I know when I can put them in the ground? When we are safe from frost? End of May?"

That probably varies by two or three weeks, depending on what part of Maine you live in. Here in the Augusta area, Memorial Day is usually taken as our "safe" frost free date. Occasionally I gamble and plant some things earlier than that.

But I actually keep an eye on our local Manchester weather forecast to decide exactly when. I usually plant out a little earlier or later depending on the circumstances. Last year it was a few days later, because it was cold or raining or both on Memorial Day and a few days after.


    Bookmark   March 10, 2007 at 2:19AM
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veilchen(5b southern Maine)

Like MM said, it depends entirely on what you are growing. If you're growing vegetables, it depends on what kind--tomatoes and peppers can't survive a frost, in or out of a greenhouse. If I have my tomatoes in the greenhouse later this spring, and the night temp is supposed to dip below freezing, I bring them inside. But some cold-weather vegetable seedlings can take it, like cabbage, broccoli, etc.

The same with flowers: most annuals can't take a frost, but there are some, like dianthus, that are ok. Perennials are fine in the cold but will do better if grown/transplanted under warmer conditions.

The date to transplant into the ground depends on what you're growing and what the weather forecast is.

Please share specifically what you want to grow and maybe I can help.

    Bookmark   March 12, 2007 at 7:06AM
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