My husband and I live in the zone 8a high desert Southwest, about 4500 foot elevation, 12-14 inches rainfall yearly. Monsoons if it's a "normal" year.
We're building a living space and had a bunch of excavation and clearing done around the homesite. We want to try three different versions of sunken greenhouses - or maybe more technically "sunken growing spaces". Sunken
greenhouse pits? Greenpits? I've been contemplating these for a couple years now, watching everything I can find on wallapinis, sunken greenhouses, and passive
greenhouse techniques used in high elevation areas in Nepal, Bolivia and China.
Unusual issues/local features:
Big Temperature swings:
It hit 110F this year and was in the hundred degree plus range for much of a month. People normally do an early garden and then a late garden here, with some growing in winter which being 8a has hard freezes. The fall and spring are lovely with days in the 60s to 90s, however, the cool nights (freezing at times) stunt the growth of many plants.
But summer is hardest as it can shut down plant growth entirely. I've "over-summered" a bunch of food plants this year, but it took a lot of
water even with shade. Many people here grow in shadehouses. Some things do fine in the full or almost full sun though, like sweet potatoes, sunchokes and winter squash. I've found that sunken beds work well and a lot of plants can be grown in the shade between or under more sun-tolerant plants. But some plants just won't make it through the summer at all.
Very rocky soil -
After seeing the rocks that came up just when our driveway was being cleared, we realized that digging these pits by hand was not going to work. We're planning on reinforcing the walls with Superadobe earthbags and that's already going to be quite a feat of labor. So we hired a neighbor with a backhoe for $70/hour and after watching the process and the really large rocks he pulled out it was so clearly worthwhile! Thank goodness for machinery! There is a lot of material to work with for the walls, but it's going to be a like working in a quarry for quite awhile.
Extremely drying winds -
Besides being very hot during much of the year, and also with cool nights and hard freezes during parts, we are in the high desert and have it's typical crazy-dehydrating winds. Plants can look like they were freeze-dried! I feel like I get freeze dried. This was my initial motivation for the sunken greenhouse pits - a sheltered place for me to garden, especially out of the wind.
We don't want to use plastic-
We're not aiming for air-tightness; we want airflow even though this means less efficiency of sorts. Our climate is mild
enough that we're hoping we can use other strategies to modulate temperature for the pits. So it's going to end up a matter of how little we can get away with (and still have things grow).
I'd first like to try vines (like a living, humidity creating shadecloth/windbreak). Then possibly the Aluminet or another cover of some sort if I'm not getting enough temperature moderation with the vines. And maybe a totally different method that I have yet to imagine. This obviously isn't a strategy of being airtight or controlling heat to the degree that requires studious airflow management, but I have certain reasons for that besides being a little lazy. :-) My husband and I are super-sensitive to certain molds (particularly those that grow on
wood,
straw, and some other plant matter) and airtight greenhouses can become a problem for us.
The end goals
The purpose of our "greenpits" and other greenhouse experiments is not exactly to hold heat, but more specifically to
create an environment. We hope this can be done by moderating temperature, reducing wind and evaporation, collecting rainwater (as runoff into the pits) and extend the growing season throughout the year for certain vegetables, fruit
trees, and nursery plants. And just as importantly , we hope this will create nice places to hang out in! Along with the greenpits, we're also doing a lean-to greenhouse against our shop (west-north-west facing by necessity... it will be interesting to see what grows best in it) and a second smaller lean-to greenhouse with a solid roof and south facing main wall. It's going to be a fascinating few years as we see what each can do!
Below are the pictures thus far. Two of the pits are oriented east west, so they are south facing. One I decided to try something different with more shade as the goal. That one is oriented north-south and is deeper than the other two. The goal for the deeper one is to mimic a forest valley and create a lot more shade, intentionally. Here in this desert some plants that would require "full" sun in Oregon can grow on the north side of a house or wall! I wouldn't have believed it if I hadn't seen it myself. So in the north-south oriented greenpit, I want to grow some trees to create a shaded, wind-free, and hopefully more humid spot that things unusual to the desert might grow in.
All ideas welcome, especially ones for innovative coverings... Thanks!
6
