Nitrogen fixers

So far what I’ve been doing at Alconasser could not really be called permaculture, more gardening with the odd permaculture twist, such as composting brush rather than burning it, mulching and not digging.  To the eyes of a Mallorquin camper it’s just lazy land management, although some have admired the veg garden and even said the fruit trees were doing OK.  The next stage, aiming at overall soil-improvement, is to do some serious planting of nitrogen fixers.  So far, other than in the veg garden, these have been confined to broad beans: edible, but annual, labor-intensive, and they don’t produce a significant amount of organic matter.  I need mulch as well as nitrogen, so perennial shrubs would be more useful.  There are a number of options available.  First of all, there’s carob.  I’m fortunate to have quite a few carob trees, and their effect on the soil beneath is striking: it’s covered in a layer of rich, black organic matter, in contrast to the stony reddish soil elsewhere.  There are a number of self-seeded carobs which I’m using for chop and drop mulch, but the tree has its limitations: it’s slow to get established and, more importantly, it does not appear to be a very efficient nitrogen fixer.  The main native leguminous shrubs are spanish broom and spiny broom, particularly the latter.  I know it can have its uses as a living fence but, after getting a thorn of this extremely spiny plant in my eye, I’m less keen to have it growing profusely around my trees.  Then there’s the introduced Sydney wattle, Acacia longifolia, which seeds itself readily wherever it appears.  This is a possibility, but I’m wary of its invasive potential and there is another tree which, in the long term, sounds more useful and just as suitable to the conditions here; the first problem being to get my hands on some seeds.

Commonly known as tagasaste or tree lucern, Cytisus proliferus is well known in Australia and New Zealand. It is a small leguminous tree providing fantastically nutritious forage (up to 30% protein, dry weight), but also useful for firewood, as a wind-break, and a soil-builder.  It is drought-tolerant, with roots are capable of extending 10 metres down to reach water and nutrients inaccessible to most plants.  It can withstand temperatures from -9 to 50˚C, so suited to vast swathes of country in both hemispheres.  Given that it is native to the Canary Islands, and would probably be as useful in much of the Iberian peninsula as it is in the southern hemisphere, it is oddly unknown in Spain.  It was a Spaniard, Dr Perez, who in 1870 tried unsuccessfully to get the Spanish authorities interested in its potential outside the Canarias.  But it found its way to Kew, and from there to the Southern hemisphere.  The rest is history.

That was getting on for a century and a half ago, and I have not managed to source seeds of this plant anywhere; a google search in Spanish only comes up with seeds in Argentina and Uruguay.  Last year I got some seed from Australia, which came with a little bag of inoculant to supply the seeds with rhizobacteria; without that the plant would have to make do with whatever rhizobacteria are present in the soil, which it may or may not be able to utilize.

Getting these shiny, black little seeds to germinate requires a bit of tough love.  The notes which Green Harvest supplied with the seeds suggest boiling or scarifying the seed, then soaking it.  I tried both techniques, the scarifying by rubbing the seeds between sandpaper, and had a more or less equal germination rate, which was not very high.  I had gone to the trouble of sourcing some sandy soil from a garden center to get these plants started and that, it seems, was a mistake.  All the tagasaste which germinated, as well as some pigeon pea, shriveled and died within a few weeks.  Meanwhile, a citrus and a sapote potted up in this stuff grew like crazy, so I come to the conclusion that this soil contained a not insignificant quantity of chemical fertilizer and was just too much for those tough legumes.  I had started late on the seeding, and by this time it was July and I figured I’d missed the window for getting them started last year.  So, 2015 and a new lot of seed and inoculant, let’s have another go.  This time I’m using soil from the ground, I reckon it’s quite free-draining enough, mixed with a bit of leaf compost.  As the brilliant Angelo Eliades writes in deepgreenpermaculture.com (check it out if you’re interested in what can be done in a tiny Melbourne back yard), people have been growing plants from seed way before bagged potting compost was around.  Time I stopped using that stuff too.