Heating the greenhouse

I have gotten a few questions about whether there is enough mass in my compost pit to heat the greenhouse, and frankly I don’t know, but probably not (see below). Although there is a lot of physics involved and there are easy calculations, there are a lot of variables that lead to uncertainty and imprecision, too, such as the following:

• Outside air temperature
• Composition of compost
• Type of manure
• Mixture (C:N)
• Type of carbon - e.g., straw, sawdust (generated from my woodworking shop)
• Frequency of turning the compost pile
• Frequency of C or N addition
• Size of greenhouse
• Insulation of greenhouse
• Thermal mass in the greenhouse (water, concrete, etc…)
• Other sources of heat

I have been researching this quite a bit, and although there are some great resources out there, I think the bottom line is I am going to have to try it and see how well it works.
Two great sources are the Physics of Composting by Cornell (it seems they have the answers to everything ) and “The Composting Greenhouse at New Alchemy Institute: A report on two years of operation and Monitoring March 1984 - January 1986”.

I based my calculations largely on the results from the above report. In essence, they used an active system to draw heat from a 25-cubic yard compost pile to heat a 576-sq. ft. hoop house. Their compost pile was composed of horse manure and sawdust (though it is not the hottest compost mixture, it is probably what I would use, plus our releatively insignificant contribution of kitchen scraps). This system gained them 23-35°F over the outside ambient winter temperature on cold, clear nights. The temperature at the highest point in their greenhouse dropped to 28°F (which I think was the lowest it got), but it did not cause problems for their lettuce (good news to me).

There is a huge range of information out there on how much compost can heat (see variables above). I estimate I will typically need between 4,100 and 8,000 BTU’s to heat the greenhouse to above 32°F in the winter (here is a great tool to begin determining your heating requirements). The range I am using in heating requirements is based on heating from low temperature between 0°F and +17 °F. Even though it does get to –30°F here, the average low temp is 17°F according to (http://www.weather.com/weather/climatology/monthly/59801?), and I used 0°F as a realistic good middle ground. I look at this range as designing for 90-95% for the time, rather than the 5% event. These BTU calculations have taken the glazing material, glazing surface area, insulation and greenhouse design into consideration.

Here are a few bits of information from various sources:

• A compost bin will produce about 1,660 BTU's/ cubic yard/ hour or 1,530 BTU/ lb
• Or heat 6-24 square feet of greenhouse/ ton of compost (interestingly, both these ratios seems validate my ratio below, too)

Another way to calculate how much compost I would need to heat the greenhouse is using the example greenhouse (from the Composting Greenhouse at New Alchemy Institute, above) because their results seemed to work for my needs. Using the ratio of of their greenhouse square footage to the quantity of compost they used was 576:25 so using that ratio, I would need about 2.6 yards of compost. My planned compost furnace is about 1 cubic yard, so my compost furnace would, in theory, supply 1/3 the heat to keep my greenhouse going in the winter.

In addition to the compost heat source I will use rain barrels as a heat sink, but perhaps more effectively, as a source of water for the plants in the greenhouse. Given the space restrictions, I will probably only use 100 gallons, or roughly 1/5 of what I would need to heat the greenhouse with passive alone (though I'd like to find out more about Glauber's salts or related). In addition to water, I will have a concrete floor, but again, the concrete will only account for a very small fraction of passive solar heating needs. The roof on the south side of the greenhouse is angled to intercept the low winter sun angle effectively (as opposed to standard, conventional kit greenhouses), so hopefully that will help. To better insulate the greenhouse, I will seasonally install a solar pool cover. I will have a ceiling fan in the greenhouse to help move the air around and finally I will rely on a thermostatically controlled oil-filled electric radiator-style heater (about 5,200 BTU’s). The heater is large enough to heat the greenhouse alone, since I roughly need between 4-8,000 BTU's (depending on outside temperature)with no other assistance.

So, knowing that one method alone will not effectively (or in the case of the electric heater, sustainably) heat the greenhouse in the winter, hopefully a combination of techniques will yield satisfactory results. Again, the main thing here is that I have no desire to grow orchids or tropical plants. In the winter I am only hoping to grow hardly vegetables- and I think I can do it with little use of the electric heater.

Plants in our landscape

Our goal has been to use plants in our landscaping that are not only native to Montana, but native to the Missoula area. Once you consider the vast size and diversity of habitats in Montana, "Montana native" quickly loses meaning. what might be native to one part of the state, may not be native- or even appropriate to plant in another part of the state. Although exclusively using Missoula area plants may seem like a limitation, even in our small yard we have over 100 species of native plants. Nevertheless, trying to keep to Missoula area plants has been a fun challenge (the challenge being trying to keep my wife from planting species that don't belong) and goal.
Since we do not irrigate our landscaping, it is important to choose plants that are drought tolerant (hence using plants that are native to the valley), but we found that plants that would normally be associated with moist areas can thrive in the absence of water if you plant them in the shade, even partial shade. On the north and east side of our house and woodworking shop we have many species that you would normally find in riparian areas.
In our south facing front yard and boulevard, we have planted the most drought tolerant species. And in the backyard that does receive some shade (from the house, mainly), we have a greater diversity of micro-climates (the main two being being hot and dry and dry and shady). Click here for a list of most of the plants in our landscape, organized by location.

Before and after

Our yard and gardens constantly change. That is one of the nice things about gardening and landscaping, plants grow, landscapes change and you can change them.

When we started landscaping our yard, it was mainly a lawn. All the trees, shrubs, flowers, and grasses are ones we planted over the last 9 years.

We started with our front yard- the most public space and have worked or reworked areas as time and out ideas have allowed. Here are a few pictures showing some of the changes. Site preparation is essential, including removing sod, installing edging, something to control weeds (like newspaper or landscape fabric- depending on the site), mulch and careful plant selection. Typically we will water the bed or area we landscape for the first season to allow plants to get established, and beyond that they are on their own. It is critical to water to get the plants established but after the first winter we have found it is really not necessary.

Top recommended native plants

We often get asked what native plant species to plant. Being a novice gardener, I like plants that are easy to grow, but I also like plants that are relatively common in the wild, and a good for wildlife. I have developed a few lists of some of my favorites for Missoula and surrounding areas.

All these plants are native to the Missoula area, are drought tolerant, and are easy to grow.

David’s native plant picks:

• Grasses
– Bluebunch wheatgrass (Agropyron spicatum)
– Prairie June grass (Koelaria cristata)
– Idaho fescue (Festuca idahoensis)
– Rough fescue (Festuca scabrella)

• Forbs
– White yarrow (Acheillia millefolium)
– Horse mint (Monarda fistulosa)
– Hairy golden aster (Chrysopsis villosa)
– Blanket flower (Gaillardia aristata)
– Blue flax (Linum lewisii)
– Wilcox’s Penstemon (Penstemon wilcoxii)

• Shrubby Shrubs
– Rubber rabbit brush (Crysothamnus nauseosa)
– Big Basin Sage (Artemesia tridentata)
– Woods Rose (Rosa woodsii)
– Golden current (Ribes aureum)
– Mock orange (Philadelphus lewisii)

• Shrubby Trees
– Red Osier Dogwood (Cornus stolonifera)
– Serviceberry (Amelanchier alnifolia)
– Chokecherry (Prunus virginiana)
– Mountain Ash (Sorbus scopulina)
– Quaking Aspen (Populus tremuloides)
– Elderberry (Sambucus cerulea)
– Hawthorne (Creatageous douglasii)

• Instant Prairie- David’s Top Ten
– Bluebunch wheatgrass (Agropyron spicatum)
– Prairie June grass (Koelaria cristata)
– Idaho fescue (Festuca idahoensis)
– White yarrow (Acheillia millefolium)
– Horse mint or bee balm (Monarda fistulosa)
– Hairy golden aster (Chrysopsis villosa)
– Blanket flower (Gaillardia aristata)
– Blue flax (Linum lewisii)
– Wilcox’s penstemon (Penstemon wilcoxii)
– Rubber rabbit brush (Crysothamnus nauseosa) or Big Basin Sage (Artemesia tridentata)

Birds in our yard

One of our greatest accomplishments in our little yard is to provide food, shelters and cover for many species of birds. Although we seasonally have feeders in our yard, the main attraction is the landscaping. Compared to our neighbors, our yard is very unique in town, very little lawn and a lot of structure. We have had over 50 species of birds in the yard- using it for different reasons, from nesting (like black capped chickadees, northern flickers, and red breasted nuthatches), to feeding (on berries, fruits, seeds, insects and other birds), to cover (from small thickets of rose and hawthorn to the small grassland of our front yard), water, and other reasons. Even in a small yard, in the middle of town, far from wilderness, you can attract a fair amount of wildlife.


Here is a list of the birds we have had in our yard- and it is a list of birds that might be likely to visit your yard (in Missoula, anyway).

• American Crow
• American Gold finch
• Black billed magpie
• Black chinned hummingbird
• Black capped chickadee
• Blue Jay
• Bohemian waxwing
• Brown creeper
• Brown headed cowbird
• Calliope hummingbird
• Cedar waxwing
• Chipping sparrow
• Common nighthawk
• Common Raven
• Common red poll
• Dark eyed junco
• Downy woodpecker
• Evening grosbeak
• Golden crowned kinglet
• Gray Catbird
• Hairy woodpecker
• Hermit thrush
• House finch
• House wren
• Lazuli bunting
• Macgillivary's warbler
• Mountain chickadee
• Mourning dove
• Nashville warbler
• Northern flicker
• Pileated woodpecker
• Pine grosbeak
• Pine sisken
• Red breasted nuthatch
• Red crossbill
• Red winged blackbird
• American Robin
• Ruby crowned kinglet
• Rufous hummingbird
• Sharpshined hawk
• Song sparrow
• Spotted towhee
• Townsend's solitaire
• Varied thrush
• Vesper sparrow
• Western tanager
• Western wood pewee
• White breasted nuthatch
• White crowned sparrow
• Wilson's warbler
• Yellow warbler

Greenhouse plans

Here are the plans for my greenhouse- still a little rough, but you should get the idea. With a couple more months of winter- the plans will inevitably evolve some more. a lot of this greenhouse was designed around the windows- these are all recycled (as are most of the building materials). So, I had to do all the plans around what I was able to accumulate.

Greenhouse

My newest garden project is a greenhouse. I have spent this winter researching and designing a small (6x10') greenhouse for our backyard. It is the greenhouse project that is largely responsible for this blog- to share ideas and get help from gardeners.

Our greenhouse will be used year round; we plan to use it to extend the growing season by a couple of months for our usual vegetables and in the winter we plan to grow hardy vegetables- nothing too fancy or exotic: lettuce, spinach, Brussels sprouts, beets, and similar. I love hot Thai peppers and this is another reason for the greenhouse, to fulfill my peppery dreams.

We do not plan on heating the greenhouse much, but we will to keep it above 35- 40 in the winter. One interesting thing we are planning is to heat the greenhouse with compost. I am not sure if it is going to work, but I am going to give it a try. The worst case scenario is we will have storage in the greenhouse and compost that actually decomposes in the winter.

For our "compost furnace" I am planning to dig a 3x3x2 ' (deep) pit in the floor of the greenhouse that will act as the compost pit. The walls will be lined with plywood and 2" rigid foam insulation so heat does not get lost to the ground. Over the top will be an expanded steel grate to walk on and allow easy watering and ventilation. I am not sure if there will be enough mass to really heat the greenhouse, but at least the compost will break down faster than it does outside in our backyard.

The rest of the greenhouse is going to be made from recycled materials as much as possible, and I have already begun accumulating various pieces. Even though I won't start building the greenhouse for a few months, most of the pieces I have had to collect ahead of time so I could design the greenhouse. I have all the windows, doors, exhaust fan, lighting, and more.

The greenhouse will be small- mainly due to our small lot, but hopefully it will be well designed and efficient. The north wall will be conventionally framed with 2x4's and insulted with r-13 fiberglass bats, the north end of the gable roof with be constructed similarly. The south wall the south slope of the roof, will be glazed and about 50% of the east and west walls will be glazed.

I am still working ion the details of the foundation, but in any case it will be insulated with 2" rigid foam, and there will be a concrete floor, except on the south end where it will be opened to the ground for a raised bed.

Soon I will post some drawings of my greenhouse plans and pictures of the piles of materials that are filling up my woodworking shop.

What we started with and what we have achieved
Our garden began as 1 ½ city lots (40’ x 135’), covered with poor quality lawn, a doghouse, a kennel area (with waist high, noxious weeds), and the exposed soil of a dog run. There was no shade; there were no structures, and there were certainly no animals. We reduced the area of our yard covered in lawn from about 2,700 square feet to less than 250 square feet, and now have abundant small wildlife and visual interest.
We have achieved a lot in our 6 summers of gardening here. The various outdoor rooms heighten the sense of space and help us utilize the entire yard for much of the year. The spaces are people-friendly: we spend a lot of time outside eating, entertaining, reading, napping, and watching wildlife. Although the garden is intimate, it functions well for both small and large groups: we have hosted parties for close to 100 people. To accommodate such a range, many spaces have dual functions. For example, the potting bench functions extremely well as wine bar and the raised beds in the vegetable garden comfortably seats over a dozen visitors.
Apart from attracting wine lovers, the whole garden is also successful at attracting and supporting wildlife; we have seen over 50 bird species, including nesting chickadees and northern flickers. We have many species of butterflies and moths, including species that must feed exclusively on specific native plants while in their caterpillar stage. During a recent garden tour reception we hosted for the Montana Native Plant Society, the center of attention for the 50 or so guests was the sighting of several spectacular (4’ long) white- lined sphinx moth caterpillars. These large and unusual insects only eat evening primroses, of which we have many. Watching crowds of visitors taking pictures of these caterpillars illustrates how exciting it is for people to connect with wildlife, even small and unassuming wildlife!
Water conservation in our dry climate is important to us, not to mention the cost savings on our water bills. Our front yard has not been watered in 2 years and the established perennial beds have not been watered in over a year. We use less than 1/3 the water of an average Missoula household. Our goal of a variation on a cottage garden is achieved with plants that are ecologically appropriate and adapted to the area.
The community has been very interested in our approach to landscaping and our garden has been featured on several garden tours. Neighbors stroll by and linger in the public front yard prairie, coming by time and again to see what is currently flowering and looking for inspiration for their dry yards. The garden continues to fill in, and we have native plants sprouting up cheerfully in areas previously occupied by thirsty lawn and knee high weeds. By using plants that are adapted to the climate, native plants thrive and appear to be lush, despite no irrigation. We are proud of creating a short grass prairie garden that is beautiful to the eye, functional for our lifestyle, attractive to our local wildlife and the arid climate in which we live.

The Planning Process
We started our garden in 1999. The front yard prairie went in first, because as excited new homeowners we wanted the front of our house to express our vision right away. Curvilinear-edged perennial and shrub beds along the margins of the backyard gave definition to the landscape and harkened of changes to come. The backyard evolved into several distinct rooms to take advantage of local microenvironments (sun, shade, etc…).
Outdoor rooms provide a way to enhance the small yard, and create intrigue and mystery with each room. Most of our garden rooms are not visible from the next- thereby the entire garden is not revealed at once. Shrubs, trees, and other structures like fences and arbors form walls between rooms, each of which is used a little differently. We have a dining room, a vegetable garden, a laundry room, hammock room, entry room (or foyer), cooking room, and perhaps most importantly, a work area devoting to potting and growing plants. By designating different rooms, the sense of space is heightened and as a result, we receive many comments about the “vastness” of our little yard.
In planning the yard, the relationship between public and private spaces was critical. Living in town, our front area is quite public, with a city sidewalk separating an 8’ wide boulevard area from the rest of our front yard. We encourage the public to feel comfortable lingering in and investigating our garden by incorporating signs, garden markers, trails, and a garden bench.
The backyard is our private area, separated from the neighbors by a 6’ cedar fence on 3 sides (we still have one side to finish), and a 4’ cedar fence on the other. In the backyard, the rooms are successively more private and intimate. Beyond the side gate is the entry into the least private foyer, leading to a living room/ cooking area, into the vegetable garden or the dining room and finally to the most secluded room- the hammock arbor (our newest room).
We placed wildlife features throughout the garden. We have 3 different birdhouses (designed specifically for northern flickers, chickadees or nuthatches, and wrens), a bat house, multiple seed feeders, suet feeders, and hummingbird feeders, and we rarely deadhead the wildflowers, preferring to provide autumn seeds for our feathered visitors. We chose native shrubs to offer both cover and berries for birds and, not surprisingly, these are seasonally our best feeders. Birdbaths, brush piles, and a standing snag (which we installed) round out our wildlife offerings. We found the snag on while on a rock hounding expedition along the Blackfoot River (we have many large rocks and small boulders throughout the garden) after a day of fishing. The snag was on the ground and not too far from the road, but alas the snag was several times too long (30’) to fit in the back of our truck. Fortunately, David had a small multi-tool in his pocket, and after scoring the trunk at the right distance from the top, and few minutes of strategically applied pressure, the 14’ snag was ours to take home.
We have many structures throughout the garden, all built by us and many constructed from recycled fence boards as we replaced sections of our fence. The structures (including arbors, trellises, privacy screen, benches, and tables) not only add visual interest and provide definition to the rooms but also make the areas more functional to sit back in and enjoy the space- they help to simply linger.

A Montana native plant garden in a small city lot

Inspirations for our garden
We love the open prairies around Missoula, Montana, where we live and work. As a result, our garden is a variation on the intimate and informal cottage garden. It is our attempt to honor the arid short grass prairie, and its wildlife, by using only plants that are locally native species, but using them in arrangements that are equally attractive to people and small wildlife. We were inspired by prairie plants’ tenacity in surviving the intermountain west, a dry climate (13” of precipitation/ year), with short, hot summers and cold winters. We have found the aesthetic of short grass prairies is underappreciated and underrepresented in garden books and magazines and thus, presented a challenge for beginning one of our own.
One of the goals for our garden has been to expand our small house (900 square feet) and provide living space outside. We created a series of rooms that allow us to enjoy the seasons both while entertaining friends and while alone in the garden. Important to us was a garden that was ecologically appropriate for dry intermountain prairies of western Montana. Equally important are places in the landscape for people.
We also got inspiration from other gardeners in town and people we met through the native plant society, and were inspired by the National Wildlife Federations backyard wildlife program, which encourages homeowners to garden with urban wildlife conservation in mind. We wanted to avoid and eventually eliminate irrigation to all but our vegetable garden while providing habitat for native birds, butterflies and other insects. Implementing our vision of a wildlife garden in our neighborhood was a challenge, but ultimately rewarding. We live on a small city lot in the very center of town, without natural wildlife corridors that some of our friends and neighbors enjoy on the urban/ wildland interface.
We are avid outdoor recreationists- we enjoy hunting, fishing, hiking, backpacking, birding, cross country skiing, and are especially fond of the native plants we experience in the area. Plants often remind us of places we find dear: shrubby penstemon recalls backpacking the Bitterroot Mountains, fescues and sage are reminders of antelope hunting on the prairie. It is nice to come home from a day on a local river and find the same twinberry, redosier dogwood and wild rose in our back yard that we saw while fishing.