Once we added our greenhouse, that sealed the deal that we need a house sitter for vacations. Taking care of the greenhouse is a judgement call, so a certain amount of automation is helpful, but a real person is essential.

Full disclosure: I am one of those people who you describe. My husband and I both work from home, so we are able to take of things in the GH very easily through the day.

Great question! That is something that really concerns me. I want a greenhouse that is resilient to many challenges and so we are building strategies into the design. Among the many years I have been researching this, here are many of the following design strategies I have come across and am seriously considering:

Passive Solar Design
Orient the greenhouse so that most of the glazing faces south and is angled to best take advantage of the sun. In the winter, the sun's lower position means its rays penetrate more deeply into the greenhouse, warming all the surfaces. The design takes advantage of this by having many heat sinks (aka "high thermal mass" or "thermal stores") which soaks up the heat, holds it and then releases it when the sun goes down, extending the heating time frame. The northern wall is heavily insulated to reduce heat loss. Starting a design with Passive Solar principles in mind is a strong first step in making your greenhouse more resilient because it is not dependent on fossil fuels for it to work. However, it has its limitations. It is great for season extension and when combined with other strategies can be used for four season growing. It all depends on where you live, your property's attributes and what you are planning on growing.

http://www.baldmtnhomes.com/McCelo.html
http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/resilient-design-passive-solar-heat
http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/making-houses-resilient-power-outages

Pit Greenhouses
This design uses the earth's stable temperature (roughly 55 degrees year round under the frost line) to maintain temperature. Just as the name implies, the greenhouse is largely underground, often with just a glass roof. By limiting the glass, you are limiting all the ways that warm air can escape and cold air can get in during the winter. The beds are all raised and the pathways are sunken which keeps the plants safely above the coldest air. The cold air sinks and then gets warmed by the earth, rises and the cycle continues. When the sun is out, it warms the thermal mass of the earth which also stores heat for the night time.

http://www.solarinnovations.com/marketing/media/Solar%20Innovations,%20Inc.%20Unveils%20Pit%20Greenhouses.pdf

Attached Greenhouses
There are many benefits to having your greenhouse attached. The convenience of simply walking from one part of your house and into the greenhouse is huge -especially in the winter with high snow- but you also have the advantage of sharing heat. When the sun is out in the winter, you can open the connecting door and let in the extra heat into your house. At night you can let your house's heat into the greenhouse. However, it is not as simple as it sounds. It is best to design a system from the outset that circulates the heat naturally -often just opening a door does not create a significant enough draft to really circulate the air. And, to really generate heat for your house, you would need it to get to temperatures too hot for the plants. So, this is not something you should count on. Also, in the winter, greenhouses generate a lot of humidity which could create problems for your house.

Subterranean Heating and Cooling System (aka "Climate Battery or "Seasonal Store")
This innovative heating system captures the hot air of the greenhouse in the summer and stores it underground; and cooler, dryer air comes up to replace it. Over the course of the summer, the earth below the greenhouse has so many BTUs stored that you can actually heat your greenhouse in the winter with summer heat. To heat a 1200 square foot space, it requires a slow moving fan that uses the equivalent amount of electricity it takes to power a large refrigerator. The fact that SHCS takes the hot humid air, puts in underground and cooler, dryer air replaces it, means that you are controlling the excess humidity -a really handy feature- and you are both cooling and heating the space with the same system. It is simply taking heat from one area, storing it, and then moving it again when needed. This is a form of Geothermal Heating only it is cheaper and it also has the dehumidifying feature so needed in a greenhouse (and the humid air of the greenhouse makes for a super efficient system because of the phase change that occurs). In terms of a power outage, I would feel comforted that my plants and trees would be sitting on top of my heat storage even if the fan that circulates the air could not operate. It would be unlikely the greenhouse would outright freeze.

http://barrettstudio.wordpress.com/2011/12/22/the-practically-zero-energy-year-round-greenhouse/
http://www.roperld.com/science/YMCAsolargreenhouse.htm
http://www.greenershelter.org/TokyoPaper.pdf
http://www.sunnyjohn.com/indexpages/shcs.htm

Geothermal
Geothermal is very similar to SHCS -rather than burning energy to produce heat, it is simply moving heat from one place to the other which is far more efficient. The upfront costs are very expensive but over the lifespan of the system it is the cheapest way of heating and has far less maintenance. For houses, the payback period is between 5 to 7 years (with government tax incentives). Unlike SHCS, Geothermal can be used to both heat the greenhouse and the house. It also has a lot of health benefits because the burning of natural gas and other sources of heat has health consequences.

http://www.citrusinthesnow.com/
http://www.greenlifeanswers.com/articles/geothermal-in-massachusetts.html

Phase Change Materials
There a number of materials that can store heat at one temperature and release it at another. Water is one of them. Often in a Passive Solar Greenhouse, there a large amount of water barrels used to absorb heat when the sun is out and then release it when the sun goes down. Many have reported great results from doing this, others not so much. The main limitation is that water takes up so much space that could be otherwise used for plants. There are other phase change materials that can store a lot more heat for a fraction of the space. And SHCS is a phase change. The hot humid air is pushed underground where is the cooler temperature forces a due point. The water vapor is release, carrying with it the heat. Sunny John (who promotes SHCS) estimates that five times the amount of heat is stored because of the phase change.

http://greenhousefashions.blogspot.com/

Thermal Solar in Radiant Heated Beds
Using thermal solar panels, you can heat water or some other liquid, and run that through a radiant heat system that heats the soil of your beds instead of the air which is much more efficient and less heat is lost through the glazing. Plants and trees need their roots to be warm more than the air around them. If their roots are toasty than they can take a fair amount of cold air from time to time. However, some plants may get out of whack because they do need a certain amount of heat in proportion to the light they receive. How you run the pipes through your soil is a bit of a design challenge. You probably don't want them directly in the soil because you can inadvertently burst a pipe when working with tools. You may be able to design it into the walls of the beds.

What I plan to do . . .

I am concerned about Peak Oil (and Peak Everything!), Climate Change and economic uncertainty and it may seem that building a greenhouse might be extravagant with such concerns but I think greenhouses will become a handy feature of a house in the future. The key is to design one that is not a resource hog!

http://www.greenbuildingadvisor.com/blogs/dept/energy-solutions/green-building-priority-9-create-resilient-houses

For awhile, I had concluded a passive solar attached pit greenhouse (with the glazing tall enough to grow fruit trees) would be the ideal design. Then I learned about SHCS and thought that I could integrate that into the design as well. However, when we finally found a property that had enough southern exposure, we find now that the high water table is probably too high and may interfere with the SHCS tubing. So, we probably won't do the pit design and I am hoping that the heat storage below will provide the freeze protection that a pit design would give us in a power outage. I am also concerned that being in Massachusetts I might not get enough solar exposure to heat the greenhouse year round. We are looking into another heat source -any suggestions?

So now we are considering geothermal. We have natural gas for our house and I am concerned that although the price of natural gas is not so bad now that in the future it will be. I also rather not use a fuel that is sometimes retrieved by fracking. Geothermal is so expensive in upfront costs that we may not be able to afford it, however, our state does offer some loans and there are federal tax incentives. Geothermal would allow us to both heat our house and greenhouse, however, we would not get the benefit of the dehumidifying that the SHCS would provide us. I'd like to do a hybrid system but we are not sure if we can afford both.

In addition, we are designing a rain catchment system with an underground cistern and a root cellar. With the typical rainfall we get in New England, we could provide all the water we need for our greenhouse, household and gardens if we have a cistern big enough to store the water during rainy periods.

As for what to do when we go away. We have a number of neighbors who are just wonderful! This spring we created a garden on our property for three households to use. We built it all together and when one of us goes away, we have each other to look after the garden plots. -I used to have to hire someone to water my garden! We plan on doing something like that for our greenhouse where we invite friends and neighbors to enjoy it on some level whether is by sharing the harvest or spending time in it on a cold wintery day to lift their spirits. Little by little, we will show them how it works so that when we go away, we'll have knowledgeable people we can count on.

Hi curly girl!!

curious if you ever built your greenhouse and what worked for you. Especially interested in the citrus trees you had planned on.

thanks!

rachel

Hi Rachel,

Just seeing this now. We did build our greenhouse :). Our Citrus trees are doing great! We ended up with a SHCS, a little bit of a Pit greenhouse design with raised beds and definitely Passive Solar. The greenhouse never goes below 50 degrees with these design features but even if it did, the citrus would still do well. Citrus likes it to get a little cold occasionally --just not freezing.

Our Avocado trees and banana plants are doing great and have produced some harvests! We also have a fig tree that is doing very well. We had Cacao for awhile but I think it was just a little too cold in the greenhouse for it. For awhile, I used soil heating cables which worked well but then we had a winter where we did not realize that the electric circuit had tripped and the tree died. We have a Star Fruit tree that survives but does not thrive. Our mango trees were never happy and died.

Overall, our greenhouse works great but what has been challenging is that we now have three kids whereas before we had just one. We also both work full time so finding time to maintain the trees can be difficult. We are now in a process of decluttering our house so that it is easy to maintain, freeing us to do more of what we love --being in our slice of heaven! I love February, March, April in the greenhouse where sometimes it is sunny but windy and cold outside and it is balmy in the greenhouse. The air smells rich and slightly humid, often with Orange blossoms. Divine!

Let me know if you have any other questions. Best wishes with your greenhouse dreams!

Sincerely,

CurlyGirl