Help planning my new solar greenhouse

[ninnymary]

Welcome to TEG Tim! :rainbow-sun I'm not even going to try to give you advise about what to grow since our climates are so different. Check with your neighbors or nurserys to see what grows well in your area and when to plant what. As far as other possible locations in which to garden, I would suggest to use your back or front yards. I know you are concerned about having grass for any future children but that is something that can be planted fairly easily. Same goes for the front yard. When you are ready to sell all you have to do is put some sod in and spruce up the yard alittle bit. I would not let these things keep you from planting in those areas if you choose to.

Go for your dream. I'm one of those that says I only lost alittle time and money. But at least I tried. Otherwise, I would never know.

Mary

 

[digitS']

It is easier to grow in a greenhouse than in the open, Collector. Of course, I can kill plants in either location but . . . you just have more control of the environment in a greenhouse.

We need Jackb to weigh in here. Not everyone uses their greenhouse for winter production. With only 8 hours of daylight in December and subzero Fahrenheit winters, it just doesn't make much sense for me to do it. I did build my current greenhouse with the idea that I would use it in winter but my plan to sell flowering potted plants just never quite came to fruition. I'm afraid I'd be paying waaayy too much money for a pound of vegetables to justify the heat and light I'd have to use to grow them.

Here is a little information on tomato growing from the University of Massachusetts. It isn't a guide but just gives you an idea of how much time it takes to produce a ripe tomato depending on the season. I'm sorry Tim, you will have to kind of turn the months around but you will see the reasoning: Scheduling a Greenhouse Tomato Crop (click)

What you see here is that it takes 16 weeks from seed for a fall harvest and 22 to 23 weeks from seed for a spring harvest. Southern New England is about as far north as you are south, Tim. You would have about as many hours of sunlight . . . . okay, add a few weeks to each because you don't have morning sun for your greenhouse.

Some people in real sunlight-challenged areas would wait many more weeks than that for a ripe tomato. That's why some folks grow African violets in a greenhouse - besides that they may like the plants. African violets can grow well and bloom with little light. Something like corn requires a good deal of light and I've never heard of growing corn in a greenhouse, altho' it is probably done for reasons other than food production. Potato clones are started in greenhouse for seed potatoes - that's the first generation. None of the potatoes that end up in our kitchens are from that initial generation. The seed potatoes will be grown in the field for a couple more seasons - each generation of seed potato decreasing in price.

There are varieties of tomatoes and other crops (cucumbers) that are specifically for greenhouse production. The humidity is so much higher in a greenhouse that they must have resistance to fungal diseases.

Well let's see, it is just after noon in Wellington and here - I'm about to move plants from my yard back into the greenhouse as the sun will set soon. You've got the same sun, Tim . . . and, the same great big full moon tonight! I hope you enjoy them both thru the remainder of the day .

Steve

Edited: Strawberries . . . I used to know a commercial greenhouse grower who had strawberries.

 

[digitS']

Oops!

Here is a vent opener that does not require electricity:

Harbor Freight (click)

digitS'

 

[timnz]

Thanks for the thoughts, the information, and the link Steve. I probably won't grow mid winter as it probably will be a bit cold, but a greenhouse will let me grow later and start earlier than most. That's interesting about the different varieties of plants available too.

We can't always get equipment that's available in the US, and if we can it's often a lot more expensive. I was just wondering if I could get some kind of automated venting system that can run on batteries rather than mains power. I can get mains out there, but it would be a little tricky.

Mary, maybe I will use some of the back yard for veges if I start to get into gardening. The area by my shed would be ideal, it'd get all day sun, it may even need shade. I'll see how I go.

I did just find this page, which suggests broccoli, potato, and spinach will grow well in a greenhouse in winter. I wonder how they'd grow there in summer if they like a cool greenhouse in winter?

 

[timnz]

I'm trying to work out how to achieve good ventilation for summer, while keeping good insulation for winter. I wonder if a removable panel of insulated plastic (like the rest of the covering) would be a good idea, leave it on in winter, take it off in summer to leave a grill showing. Would that work?

I'm also curious about whether I need a window up the top of the greenhouse, or if I can use a window beside the door (or the door) and a window at the far end of the greenhouse up quite high. I understand that without good ventilation in summer the plants will get too hot and will cook or burn. Either way I want to make sure that I can add a thermostat operated vent later, even if I don't start with one. Any pointers?

As always, thanks for any thoughts

 

[digitS']

This is mostly conjecture, Tim, altho' I've had experience with the backyard greenhouses, beginning about 20 years ago. Sometime before that, I worked in a commercial greenhouse for several years.

At one time and maybe continuing, the makers of greenhouses seemed to be making some fairly wild claims about their products. The ads talked about the ability to allow light, filter just the right light thru or, almost, gather light for the greenhouse interior. I think these crazy notions were mostly a matter of my interpretation and the inability of the manufactures to write clearly about their glazing materials.

There are differences in glazing material and light transmission can be tested. There probably are no standards in this country of what is important to the plants and maybe even what can be said about test results. I finally came to just think of it as a rule of thumb: 1 layer of most any kind of glazing reduces light to the plants at about 10% of the outdoors. Two layers would then be 20%.

Of course, a single layer holds in heat but it does a very poor job of it. Still, there is a loss of not only the light needed for photosynthesis but solar heat gain with additional layers. If the layers are too close together, the air space is inadequate for good insulation. And yet, if you have 4 inches between layers (usually recommended), that means you have 4 inch glazing bars. And, that means you have quite a bit of shade from the bars.

All these things become trade-offs. The span, roof peak to foundation, is about 10' for my current greenhouse and I initially wanted to use double layers of plastic film. So, I used 4" bars. I'm afraid I ended up with a poor choice since I've chosen to never run the greenhouse in the winter (except for a few weeks in late winter for the plant starts). The bars create quite a lot of interior shade. If I tried to save some money on heating during the spring with double layers of film - I'd cut down on what has proven to me to be inadequate light. Yes, I could set up supplemental lighting but then I've got the fixtures blocking the sun . . . .

I am just suggesting that you look at your limiting factors and decide which are most important. You may not want to go the double glazing route. With glazing bars that are not especially long, you may want them quite narrow and somewhat wide apart. If wind is an important factor, that might be problematic but it would depend on your location. There may be a possibility of "retrofitting" with putting in double glazing on the interior or even adding additional glazing bars if things don't quite turn out the way you'd hoped or planned.

Shade cloth may be available to you to stretch over the structure in the summer. It used to be that greenhouses here were commonly whitewashed if they were used during the summer months. I don't know why that was discontinued.

With a greenhouse as small as you are planning, windows as large and high as you can get them should be adequate for ventilation in all but the hottest weeks. You may want to replace one window with an exhaust fan in the future and you should be able to go entirely with a roof vent instead of windows. That would be true even with a large structure. However, without some automation, you will need to be very attentive during the daylight hours.

Steve
On a much lighter note . . .

 

[timnz]

Thanks Steve, I appreciate the thought. I've already chosen my material, a 6-10mm plastic with an air gap that gives an effect similar to double glazing, but with much less shade, cheaper, lighter, and easier. I figure I won't be growing in the middle of winter anyway, but it'll help extend the growing season. I'm leaning toward a wooden frame, probably made from reused wood mostly to keep the price down.

I could put vents in the roof, I've found solar ones that need no electricity that would be perfect. I expect I'll need openings low down so air can be drawn through, but that should be simple enough to arrange with the builder. Like I said, perhaps a grill that has an insulated part of the wall that can be taken off in summer, left on in winter, but I'll have to experiment with it.

Given I'm probably going to put in a concrete floor I wonder if I should put some kind of under floor heating in... though it may be overkill. Any thoughts?

 

[digitS']

I have a fan close to the air intake - unfortunately, it is my furnace fan. It can be set for cooling so I usually set it at about 25C (high 70's F) during the daytime. That furnace fan has never broken in the 14 years since I've had heat in the greenhouse but one repair charge for that furnace was $300 and I would like to put off a repeat of that :/. Besides, if the temperature in the greenhouse is on its way above 25C, I will want the exhaust fan on. So, the furnace fan is just cooling by stirring the air, then I shut it off.

Greenhouse temperature may well be going above 25C while the outside temperature is below 10C (50F) . . ! Now, I'm in trouble . I don't want any 5C air coming into the greenhouse!! I don't want 10C air in there, especially if it has already hit 25C!

There's where your automatic vent openers can come in handy, Tim. Let the hot air out. It will be under pressure so not much cool air will have to replace it and it can do so, slowly.

The vent will handle that. Hot air out - mostly; cool air in - a little. A vent down low on a wall will allow an immediate rush of air to invade the greenhouse. If that air is only 5C - that won't be good. If the outside air is 20C - it will be a good thing.

No thoughts on a heated floor. Our ground water is about 10C, year-around. I've wondered how I might be able to use that for both heating and cooling but the risk of freezing pipes in the winter has deterred me from trying anything.

Steve

 

[timnz]

Thanks for that Steve. Without mains power I'm limited to a solar powered fan, which seem a bit expensive. I think a bit of DIY might do it, just hook a solar panel up to a sealed lead acid battery, and hook that up to a fan with a thermostat and louvers. How hard could it possible be?! Otherwise commercial ones are a few hundred dollars.

Automatic vent openers will help a lot, and will limit the size of the fan I need. I may get away without a fan at all, if I use some kind of shade cloth in summer and have enough vents. Maybe. I guess I'll have to experiment