Food Production in Small Spaces: Fig Trees in Zone 6

I know the posts on my backyard food production challenge have been rather thin on the ground.  But I hope to make up for that somewhat with this post and a few others I have up my sleeve.  The technique outlined here pushes the edge of the envelope not only in terms of food production in limited spaces, but also in terms of cultivating plants outside of their normal hardiness zone tolerances. 

The hardiest figs are generally considered to do well in zone 7 or higher.  I'm in zone 6b.  Early last spring a hardcore gardener in my area showed me his Brown Turkey fig trees that he had planted in large tubs and pulled into his garage over the winter months. Though fig trees can reach 6 meters in height, these were only 2 meters, at most, above the level of the soil in their containers.  I was impressed and fascinated, enough so that this concept made it on my official list of goals for 2010.  Having taken up the challenge of feeding ourselves as much as possible from our own production, while also making a conscious effort to reduce our food miles and eat locally, some of our favorite items of produce have become rather scarce in our diet. We've lamented the fact that we could not grow avocados, mangos, or figs. Until we saw this method for keeping fig trees, that is.

I'm going to walk through this technique as logically as I can, though I'm not sure the pictures I have are going to make it flow very well.  Bear with me, and click on any of the pictures for bigger scale.  The basic idea is a large planting container with a water reservoir at the bottom which is kept filled as constantly as feasible.  The soil and the roots of the plant are held up above this reservoir with the use of wire mesh and burlap.  The burlap also serves to wick moisture up to the soil as the level of water in the reservoir falls away from direct contact with the soil.

The gardener who showed me his fig trees explained that one key issue was to make sure that the container the trees were planted in was UV resistant, otherwise the sun would make the plastic brittle enough to crack and break easily after very little time.  Having handles on the containers is also a really good idea, since they will need to be moved twice a year and will get quite heavy indeed as the plant grows.  He was using slices of large diameter PVC pipe to create the water reservoir at the bottom of the container. But this site (which includes designs for a different but similar self-watering container) argues against the use of PVC in container gardening, because it leaches harmful chemicals, including endocrine disruptors. Good to know, but who knows what's in the plastic planter itself.

I broke down and bought feeding buckets for large livestock at Tractor Supply to use as the containers.  Rather than using PVC for the water reservoir, I asked friends to save a bunch of dog food cans for me. Any tall can would do just as well, but it's important that all the cans in a given container be of identical or nearly identical height.  To allow water to move freely within the reservoir, I drilled a hole towards one end of each can on the side and another on the bottom, and arranged them all upright in the barrel. A few cans were made such that a can opener could be used to remove the bottom of the can as easily as the top.  Where I could, I did so.  The cans also have the virtue of not costing me any extra money.

Over the layer of cans goes a piece of hardware cloth, to help support the soil in a tidy layer. The hardware cloth was cut using a cardboard template traced from the bottom of the container.  After tracing and cutting the cardboard, check to make sure it's a good fit within the container over the top of the cans before cutting the wire to fit.  Over and around the wire netting goes a piece of burlap. The burlap must be sized to overhang the wire netting by enough to reach the bottom of the container. Burlap also has the virtue of turning up as packaging for various items. If you buy basmati rice in those 10-pound bags, there's a source of burlap that you won't pay extra for. If you can't find any for free, burlap is one of the cheapest fabrics you can buy. 

An overspill hole is needed at just the level of the hardware cloth netting.  This is to keep the roots from getting waterlogged.  I first drilled a normal hole and then used that hole as a guide for a mandrel drill bit which significantly enlarged the hole.  I wanted something that would allow me to easily check the water level with my finger and accommodate a garden hose.  Since I'll be sticking my finger in there fairly often, and since the hardware cloth is right at the level of the overspill hole, I took the precaution of crimping back the sharp ends of the wire so my fingers aren't at risk.

A watering tube is an option for filling the reservoir if you don't want to fill through the overspill hole.  This is a tube that sticks up above the soil in the container and empties into the water reservoir.  You could use bamboo if you have access to an aggressive stand that needs thinning. You'll just need to punch through the interior segments to make it work as a pipe. The bamboo will rot fairly quickly in damp soil, but it is non-toxic and cheap enough to replace each year if need be.  To make sure that the water flows easily into the reservoir, the bottom of the bamboo pole should be cut at an angle.  Angling the top in the same way also makes filling a bit easier.  However, I'm opting to forgo a watering tube entirely.  Instead, I'll be adding the water via the hole I use to monitor the reservoir levels.  Given that I'll have only a few containers to monitor for water reserves, I think this is fine.  If I had dozens of such plantings, I'd probably opt for the watering tubes.  I was told that a fig tree grown to full size for such a container will empty a such a reservoir in two or three days of hot weather.

I was also told that the roots of the potted fig trees will need to be pruned back severely about every three years, as the plant grows out and fills the container.  The guy who sold me the fig trees said this could even be done with a chain saw!  I suppose this root trimming works along the same lines as bonsai cultivation does. Pulling out a fig tree whose root ball has managed to fill a twenty-odd gallon container is going to require two people, no doubt, even with the container laid on its side. But it will also be an opportunity to check that the burlap is still intact, and to add some worm castings to the container to feed the tree.

So last Friday I came home from Flemington, New Jersey with three one-year-old fig trees: one each of the Neri II, Sicilian, and Verte varieties.  Fig trees like an alkaline soil in the 7.5-8.0 range, so I added finely crushed eggshell (a homegrown product) to the garden soil and compost mixture that I made for the fig tree containers. This study shows that pound for pound eggshells are nearly as effective as garden lime at lowering the pH of soils. Eggshells affect soil pH a little more slowly, but the effect is longer-lasting.  I was told to expect a small crop of fruits this year. The trees have shown really dramatic leaf production in the few days I've had them in their large containers.  We'll see how it goes as far as a harvest is concerned.

Aside from the fact that I'll be able to pull my fig trees into our garage for protection from winter weather, planting them in containers means that they can be placed on a driveway, porch, or any other space not otherwise useful for food production.  When we try to maximize what we produce in limited residential spaces, we need to use all available space, whether it looks suitable for cultivation or not.  Container gardening is one of the most versatile means of doing so.  Theoretically, these trees in large containers could be moved if we were to relocate. I don't expect we will anytime soon. But if you aspire to food production in a rented space or if you anticipate moving in the near future, this self-watering container for fruit trees is one you might consider. Just be aware that containers of the size I show here will weigh a couple hundred pounds when full of soil and a tree grown to the limits of that container.

I'm posting this technique at just the moment I'm trying it out for myself, because I've seen first hand that it works for this particular tree in my immediate area.  There may be a few tweaks and modifications I will recommend in a year's time.  But I wanted to get this idea out there for those of you thinking about what can be done in small spaces or in a cold hardiness zone.  Also, for what it's worth, it's apparently not too hard to grow new fig trees from cuttings.  So if you "invest" in a fig tree or two now, you could in theory have figs for the rest of your life, or share the wealth by passing on new trees to your community.  That's my kind of investment.