Greenhouses where it is cold for a long time...

The purpose of my question:  I want to set up a system that will yield fruits and veggies 365 days a year, at about the same rate.  This will minimize the need to can, dehydrate, freeze dry or freeze.  I have seen a lot of greenhouses....all have lots of transparent/translucent roofs to let lots of sun in.  For those of you who have a green house in a zone 4, 5 or 6, do you try to do this?  or just use your gh to get a head start on spring?  Feel free to give me terminology to search in giggle :)

Hi Tom,
I typically use my greenhouse for starts and then use it for chickens in the winter. There are a number of ways to accomplish what you are describing, but most of them will require quite a bit of time and work to build insulations walls, heat storage, heat producing devices, etc.

Probably the simplest concept I think would come from Eliot Coleman who lives here in Maine and wrote a book called 4 season harvest. You will notice he did not call it 4 season growing. But by changing up a little of what we grow and using a greenhouse and row cover, he is cable to harvest vegetables all year round. Changing some of what vegetables you grow is part of it too. You are not going to be growing a tomato, even in a greenhouse, in Maine during the winter without a source of heat.

**Edit
It is like the story of growing a lemon tree in the alps. Can you do it? Yes... is your time better spent on growing something that will grow more easily? Perhaps. I think you can absolutely do what you are talking about, but I worry trying to grow "normal" vegetables in a "normal" greenhouse may require more effort than you want to invest for the output you get.

Eliot Coleman is definitely the right starting point. The other thing worth looking at is a double-skin polytunnel — the air gap between two layers holds heat surprisingly well and cuts heating costs significantly in zone 4/5 winters. Combined with cold-hardy crops like spinach, kale, mache and claytonia you can get genuinely usable harvests through the worst months without much heating at all.

Tom Connolly wrote:  I want to set up a system that will yield fruits and veggies 365 days a year, at about the same rate.  

There are more factors than just "cold" that is going to affect yields. The big factor in the Pacific North West is that there's not just "less" sun, but what little sun there is, is dispersed and reduced further by cloud cover. That means you will need more greenhouse glazing in the shoulder seasons than sunnier locations, and major lighting for the 3 darkest months - Nov. Dec, and January - if you want new growth and fruit to ripen.

I tried growing lettuce in my large south window in Dec one year, with grow lights to supplement the day length and it sat there and did nothing. I have been told by people trying the Coleman method, that his veggies don't actually "grow" much in the winter, they just hold what growth they made in the fall. So greens that can do that (kale and Swiss chard for 2 examples) can be picked as you need them, but they won't do much if any growing of new leaves. Some varieties of lettuce hold in the cold well, but some don't.

I am not sure what fruit will hold and ripen in the cold season.

Are you in an ecosystem where a good cold room can be built? There is very little work in storing veggies in damp sand or sawdust until they're needed. Different veggies need different conditions, but squash, potatoes, apples, etc can provide food, while a small greenhouse can provide a bit of variety.

The YouTube channel arkopia has a good series on building a passive solar greenhouse in Canada.

Eliot Coleman does talk about minimum light requirements, but I can’t find the YouTube where it is all in one place. He did do a podcast with his daughter that covered a lot of it.

If I were in this situation I would want a rocket mass heater to keep the greenhouse warm.

There are 2 things for winter greenhouses that need to be taken into account:
1. heat
2. light
Although solar gain will do well enough on its own on a sunny day, it will take much more energy to make heat at night and cloudy days than it takes to provide lights.  Another factor for northern greenhouses in winter is snow load and the structure needed to support that weight. While the snow does insulate, it blocks any available light from reaching the plants and so will need to be removed. After more than 45 years of living and gardening in Wisconsin and Minnesota, I've come too the conclusion that a greenhouse in midwinter isn't worth the effort. Instead we've taken advantage of the large south-facing windows in our house, a space that is already being heated, and rigged up shelves and lights to get through from November to early March, and use a very small non-heated greenhouse to cover the "shoulder" seasons. Greenhouses with vertical glazing (glass) don't have to worry about snow load, plastics degrading, and are easier to keep warm with insulated roofs and walls and a simple, 2 layer curtain over the glass at night (ours is a cotton painter's tarp). Supplemental lighting helps here as well. The crops for the indoor window garden and greenhouse spring and fall are primarily leafy greens (lettuce, non-heading napa, spinach, bok choy, celery, etc.). In the fall, as the light starts to fade, crops need to be started early enough that they are "mature" by Halloween and will hold until harvest over the next few weeks, with greenhouse crops picked out first before serious cold sets in. After the Solstice, the indoor plantings will have been picked out and it's time to switch to trays of microgreens until new plantings in about mid January start to produce harvests. As weather begins to warm in March, plantings can be established once again in the greenhouse.

Most importantly, there are no fruiting crops to harvest in winter greenhouses in the upper midwest. Eating seasonally is the biggests hurdle in one's thinking of how to approach a year-round, nutritious menu. Fresh greens go a long way in adding to a root-cellar and preserved foods based diet.

Hi Tom,
If you are in SW Washington, aren't your winters very gray and cloudy?  I think light might be the limiting factor for you (more than heat).  Plus for plants to grow and not just hibernate you need more than 10-hour day-lengths. To reach 11-hr days in your area you need to wait till March to plant.

I've had a greenhouse for ten years now and I can easily identify the three limiting factors working against productivity in the winter months. Heat is the least of my worries, since the climate here is so mild. I can run the RMH on cold nights and keep the temperature well above freezing despite the single layer of thin glass radiating all the heat away.

The bigger issues I need to solve if I want to get a better yield are humidity control and light. Even though I cut back on watering in the cooler months, the inside of the glasshouse is close to saturation most of the time. I have to remember to open things up in late morning and close it down by midafternoon to air it out, and even with this habit a lot of plants suffer from fungal and bacterial incursions. I've been brainstorming some sort of air exchange that will help mitigate this.

Light levels are the other major limiting factor. No point trying to grow warm-season crops under glass if they're only getting a few hours of sunshine at best, and little or none on cloudy days. So I need to put in LEDs for augmentation purposes, and then dedicate a power source with enough headroom to get through a week of stormy weather. Bonus points if this setup can also drive a bit of active air circulation to help me get on top of the humidity situation.

That's Why growing in winter is more of myth than reality.  If you must grow in Winter do it inside a grow tent with lights indoors.

My unheated and non-lighted greenhouse provides green-leafy food all winter in northern Utah.

Anne Miller wrote:If I were in this situation I would want a rocket mass heater to keep the greenhouse warm.

That's what I've done in my 12x19ft polytunnel greenhouse in rural Ottawa. I designed and built a "shorty" stove (Thanks for the advice, Peter!) that warms a bench made of salvaged concrete patio slabs and filled with stones and gravel.

That's not enough to warm the entire space in our truly cold weather, so I built a smaller plastic covered greenhouse within it, leaving the stove outside it in a "vestibule". A small fan heater with a thermostat adds enough supplemental heat to ensure it doesn't freeze in the coldest weather (~-30C).

That's my setup for cool and cold weather. Summer overheating is a different problem to solve.

Phil Stevens wrote:
...
The bigger issues I need to solve if I want to get a better yield are humidity control and light.
...

I don't have as severe a humidity issue, but I've learned that air movement is important to reducing fungal problems. An oscillating fan has been a big help.

The honest answer for zones 4–6 is that 365-day growing is possible, but it's usually a heating-bill decision more than a gardening-skill decision. Once you're keeping a greenhouse above ~4C through December–February, you're paying for every degree, and the size of that bill decides whether a head-start-only greenhouse is the better choice.

I would run my actual greenhouse size and glazing through a heating cost calculator. This one estimates the seasonal cost for any size/zip combo: https://comparegreenhouse.com/tools/heating-cost-calculator If the winter number makes you wince, the Eliot Coleman approach Paul and others mention above — hardy crops + row cover instead of heat — is usually the better permie answer anyway.