Growing fruit trees under cover...

Hey Permies!
I am currently looking for viable options to make money off some land in the alpine regions of the South Island of New Zealand. I want to know if anyone has any experience or knows of growing fruit trees in tunnel houses for the purpose of growing varieties which do not usually grow so well in that climate zone.

I ask this because I once rented a property in the far south (cold and temperate, not a lot of sun and loads of rain) which had a tunnel house in which grew feijoas, figs and some dwarf citrus'. These were unheard of in that area and did very well under cover.

Now I am in a hot and dry alpine region and am toying with the idea of doing something similar but on a larger scale and would love to know if this is very common in Permaculture and organics as the only operations I have found are very Sterile, monocultural set ups which do not appeal to me one bit.

Any info or resources would be much appreciated
Thanks!
Tom

Hi Thomas,

I don't see why it would not work. And why you could not simply use a more nature way of farming to build soil and encourage polyculture.

The way I think of it, you are creating a micro climate. You can do this with natural methods (Sepp Holzer has many good examples of this) or with man-made materials.

As you are probably familiar, dwarf trees are small and quick to get into production. So they seem well suited to your situation and goals.

I encourage you to think toward a design where the poly tunnels are connected to a dwelling, to make use of the thermal mass and additional heat. Also, adding a lot of thermal mass into the covered areas will help increase the suitability of the mico-climate.

remember also that most types of artificial covering will degrade overtime. being aware of the condition of the plastic, and changing it out when the climate outside won't kill your crops, is an important management practice.

Sorry I do not have external resources... but you should check out Sepp Holzer's work. While he does not use artificial materials, he writes in detail about creating micro-climates.

I live in Oregon and I grow dwarf Peaches (Patio Peach) and Mexican Limes in pots inside my unheated greenhouse. The Peach trees don't get Peach-leaf Curl disease and the Lime trees had an abundant crop of limes this winter. (I did have to bring the Lime trees into the house during the deep freeze back in December.) One of my Mason Bee houses is in the greenhouse, so they often do all the pollination for me. I'm also growing Figs from cuttings in my greenhouse and I plan to grow the more tropical varieties such as Conadria in big pots in there this year as well. I know some folks don't like greenhouses, but they are really nice to have in my cool, mild climate. Sometimes people give the plastic ones away or you can make your own from used window frames and scrap wood. I've seen some really nice homemade greenhouses that people made from all recycled materials for next to nothing. They can give you the chance to grow trees from warmer/drier climate zones. Andrew has a good idea about building them next to your house for extra heat. Good luck!

Hey Thomas,

Interesting idea. I grow cool-tolerant greens in an unheated hoop house and am building another hoop house that will incorporate solar heated radiant root zone heating for germinating and growing flats of various vegetables to be transplanted so as to extend the moderately short growing season around here. I have no experience with trees or semi-tropical plants in a greenhouse, but feel you could certainly succeed with your vision. It will probably take a well designed system.

A tunnel house, hoop house, poly tunnel, high tunnel etc. can harvest a lot of solar energy which can be stored for release when temperatures drop. Even so the minimum nightly temperatures in my hoop house are typically equal to those outside. I have been able to keep greens alive at low temperatures down to 18 F below zero (-22 C ?) but it requires attention morning and evening. The basic technique is cover the plants with row cover (multiple layers depending on expected low temperature) on pvc hoops--low tunnels inside the hoop house. The plants are uncovered during the day so the soil is warmed by the sun; this stored heat is released at night and protected from radiating into the atmosphere by the row cover blanket. Perhaps the leaf canopy of your fruit trees will keep some of the soil's heat from escaping into the atmosphere. On the other hand the leaves will tend to shade the soil during the day, perhaps decreasing the amount of heat captured by the soil. If your climate is much warmer or not as elevated--7600 feet--then you may not have to worry about nighttime lows so much and can store enough heat just in the soil.

Daily covering and uncovering doesn't seem very practical for even dwarf fruit trees. It also doesn't really do the trick for producing tomato, peppers, melons, cucumbers or other warm weather crops as they like air temperatures above 50 F/10 C. Some days the soil doesn't heat up much above 50 and the air temps will drop well into the 40's, even the 30's the following night. Fine for greens, but maybe not for your fruit trees. So I came up with radiant root zone heating to get this additional warmth. I still plan on a low tunnel within hoop house model, but you can also heat the air in a greenhouse with this method. It just requires more hot water.

The basic set up is to pump warm or hot water through pipes looped on six inch centers beneath the soil. The loops can be deep enough to grow plants in the bed or only a couple of inches where flats or pots are placed on the surface. Keeping the soil in flats or pots at 60-70 F/15-20 C requires 15 to 20 Btus per square foot per hour. Heating the air in a greenhouse would require 3 to 4 times more heat. A variety of heat sources can be used to generate the hot water needed. A regular domestic water heater would be just enough for my 500 square foot green house. I'm going to use solar in two stages.

I have a 1600 gallon black plastic water tank--7.5 feet in diameter and almost 6 feet tall, with a domed top. I've been following the temperature of the water in it the last 10 days or so. On a sunny day, temps in the low 40's, uninsulated--though protected from wind on the north side--it gains about 100,000 Btus and loses most or all or more than that each night (mid-teens). Yesterday I insulated the north half of it and enclosed the south half within the hoop house with foil covered insulation angled to reflect additional sunlight onto the tank. Last night it lost 24,000 Btus and today it gained 70,000 Btus even though it was cloudy half the day. I figure enclosing it in a green house will increase the heat gained rather significantly and insulating it has drastically reduced losses at night. I'll begin to find out how much in a couple of days when the plastic goes up on the 40x13 foot structure. As it is 70,000 Btus is sufficient to keep my flats warm enough for about 16 hours. I do have to gain that heat from a higher baseline, but I'm counting on the insulation ratcheting the temp up. I also have the use of several parabolic trough solar collectors that should greatly increase the daily heat gain, ensure that I have enough stored heat to make it through several cloudy days in a row and maybe heat the air enough for a fig tree!

Root Zone Heating is a decent introduction to the topic. Greenhouses: Heating, Cooling and Ventilation has charts and formulas and walks you through the process of calculating the heat loss from your greenhouse based on materials used in construction and the amount of heat you'll need to add based on your heat loss, your average low temperatures and your target growing temperatures. Subterranean Heating and Cooling System Explained describes a way to cycle warm, moist air during the day through pipes buried beneath your greenhouse then recycling it at night to heat the greenhouse. Seems like a way to get around any reduction in soil heat due to shading issues.

Greenhouses excel at solar gain on sunny days; on cloudy days they hold their own and a little more; at night they lose heat at a rate far beyond what most people would find acceptable in a residence. Perhaps if your house has a sustainable source of heat that is capable of generating significantly more heat than you need for your house on the coldest nights--when your greenhouse needs the most supplemental heat--then you could consider whether it is a more efficient means of heating your greenhouse than any system you could design for your greenhouse. Even if you have heating capacity to spare, you have to distribute that heat to where your trees can use it. It may well be that the minimum target temperature for your greenhouse will not feel comfortable in the nearby part of your house, but maybe that's OK. Lining an insulated north wall with 55 gallon barrels painted flat black and filled with water is likely to be a far better heat storage device than any thermal mass your house has to spare. Not to mention the heat such a wall would harvest on a sunny day, or that it stores the heat near the trees. From a practical standpoint although maybe it's just the extreme environment in the high desert, but I don't understand the attraction of adding a greenhouse onto your house.