Fruit Trees need their Nutrient Fix

Nutrient junkies need their fix….

This planting season will see a few new species on the Urban Orchard Project tree order lists. We’ve decided to plant at least one nitrogen fixing shrub into each of our future orchard designs to build fertility into each orchard system.

Degraded Soils

Many of the soils we deal with are degraded and compacted meaning that we have an uphill struggle from the start when we’re planting demanding crops like top fruit. Most of the fruit we eat today is ‘improved’, that is it has been developed by human tinkering over many centuries to produce the larger, tastier, cultivars that we enjoy today. We ask a lot of the fruit trees that bear such fruit; like the improved vegetables we now eat they require more nutrient input than their wild ancestors. Indeed, some community orchards in London are now at an age where we’d expect to see more fruit, but they’re not performing too well. This is could be due to a lack of nutrients, although drought may also be having an impact *.

A Permaculture Solution

Permaculture design seeks to create truly sustainable systems where the need for external inputs, such as fertiliser from an off-site source, is reduced. In the case of an urban orchard, suitable fertilisers may include manure from an urban farm or stables. Let’s consider manure as an example for a typical community orchard group. First a source must be located and arrangements made for a load to be picked up. Then a vehicle must be found to drive to the pick-up point to transport a large amount of this bulky, heavy material. Much effort must be put into shovelling the manure, first into large bags to be loaded, and then again to haul them off at the orchard site where it must then be distributed to each of the trees. All in all that is a significant amount of energy, both human and fossil fuel. Alas, the feeding part has probably been neglected by some groups largely due to the hassle factor.

Nitrogen Fixing Shrubs

Surely, a sustainable system would be one that provides its own nutrition, that is, it has fertility designed into it? Enter the nitrogen-fixing shrubs. Plants of this Actinorhizal group have the ability to form a symbiosis with nitrogen fixing bacteria Frankia which take up residence on their root nodules. These bacteria can fix atmospheric nitrogen into a form that is then available for other plants to utilise. The plant fixes enough for its own needs, and, in an act of Gaian magnanimity, provides surplus to be shared with the wider ecosystem. This is distributed to the other plants in form of leaf fall, prunings, root ‘sloughing off’ and shared around by the mycorrhizal network.

This ability makes the actinorhizal plants pioneer species; they colonise nutrient-poor soils where they then build the fertility by adding nitrogen which eventually allows other plants to move in and ecological succession to continue.

Added Benefits

As added benefits, there are some species that also provide nutritious fruits. Plants of the Elaeagnus genus produce berries rich in the phytochemical Lypocene which has anti-cancer properties. Sea Buckthorn, is another, and produce abundant berries high in vitamin C and beneficial carotenoids. Both can be used in juices and jams.

Both of these shrubs can be planted on most soil types, including degraded city soils. They can also be used effectively as windbreaks.

So, we’ve decided that all of our orchards would benefit by having at least one of these multi-functional wonder shrubs added to the line-up. We also aim to under plant each fruit tree, in both future and past orchards, with Bocking 14 comfrey to provide a regular fix of potassium and phosphorus when the leaves are ‘chopped & dropped’ into the mulch zone.

We’ll then be observing any difference in the cropping patterns of the fruit trees. We’d love to hear from anyone who’s also experimenting with actinorhizal shrubs in food systems in the London area, in particular around different species and soil types and any observable differences in resulting yields.

Lewis

* As we were about to publish this blog I heard from our friend Russell Miller of the Tree Muskateers who recently participated in Radio 4’s Gardener’s Question Time at Dalston Curve Garden. Whilst giving an interview, Russell asked for the opinions of both Bob Flowerdew and James Wong on the link between low nutrients and low yield. They thought that if the trees are flowering and show no signs of nutrient deficiency in their leaf, then lack of water is likely to be the reason for poor fruiting, with many urban orchards planted on well drained, rubbly sites. Either way, feeding our fruit trees is still an issue which needs to be tackled, and planting N-fixers should help to create more diverse and resilient food systems.