In spring, the soil in my mountain garden in southern Valencia is covered with what most farmers would call malas hierbas — bad herbs. In other words — weeds. Emulating what our neighbours do, we’ve been mowing these winter- and spring-growing plants — until I discovered that many of these malas hierbas, far from being bad, are actually good. Exceedingly good, in fact. After two years of observing the garden, I’ve come to realize that it holds undervalued treasures — in the form of the loveliest wildflowers: pink and white cistuses, blue-flowered Aphyllanthes monspelliensis, called falso junquillo locally, primrose coloured Urospermum delachampii, and many, many more. The cistuses have only begun to bloom this year.
On this, our third spring here, I’ve been examining the “weeds” more closely, and I recognize some as legumes, i.e., belonging to the bean family (Fabaceae or Leguminosae), from their flowers that resemble sweet peas. These leguminous plants are even more valuable garden treasures than pretty wild flowers. Not only do they also have colourful flowers, but they have a very important role in the garden. They are extremely beneficial to the soil, since they can fix atmospheric nitrogen in symbiosis with certain soil bacteria, such as rhizobia (sing. rhizobium).
Nitrogen is the mineral that plants need the most. Although nitrogen makes up close to 80% of the earth’s atmosphere, it does not become accessible to plants until it is converted by bacteria into ionic forms, such as ammonium and nitrate, in a process called biological nitrogen fixation (BNF). Lightning carries out some of this natural conversion as well, but the bulk of BNF is carried out by soil- (and also water-) living bacteria in symbiosis with certain plants, mainly leguminous ones. The bacteria stimulate their host plants to form nodules on their roots (some on stems). Within the nodules, BNF takes place, supplying the host plant with nitrogenous compounds that it can use. Nitrogen can also be supplied through chemical fertilizers, but I much prefer organic sources such as well-rotted manure and the natural process of BNF.
The size of the wild legumes in my garden varies from creepers — no taller than 5 or 6 centimeters — to low shrubs about half a meter high. Their flowers also vary from being no bigger than the nail on my little finger to the width of the first joint of my thumb.
Last year I noticed a volunteer plant with tiny leaves. Curious, I allowed it to grow to see how it would develop. It has now grown into a bush, half a meter high, and is prolifically blooming. Its clover-like flowers and the wooliness of its stems and leaves have enabled me to identify it — Dorycnium hirsutum (la botja). It turns out to be a really outstanding plant, having received an award of garden merit (AGM) from the UK’s Royal Horticulture Society. Fortuitously, it belongs to the legume family. So not only does it add fertility to the soil, but its flowers are irresistible to bees — a great plus when bees’ pollen sources are becoming increasingly depleted. Bumble bees, honey bees, and other pollen seekers happily forage among the dorycnium’s flowers. I’m so glad I did not consider it a weed and pull it out last year.
Last autumn I sowed seeds of recommended nitrogen-building legumes — red and white clover and lupines (Lupinus angustifolius), but they haven’t done well. It stands to reason: these seeds from Germany have been harvested from plants grown in a moister environment. However, with these endemic wild legumes that many would dismiss as weeds, Nature has ensured that the garden has its own reliable and rich sources of nitrogen. Another unlikely source are the dark green gelatinous lumps that often appear on the gravel path after heavy rain. These are free-living nitrogen-fixing cyanobacteria, called nostoc.
I love seeing these diverse native nitrogen fixers that in my ignorance I would once have regarded as weeds. These are indeed treasures to the permaculturist and anyone who wishes to garden sustainably. Serendipitously these nitrogen fixers often position themselves next to domesticated plants that would most benefit from the symbiosis.
Recently, an unusual leguminous plant with fuzzy seed heads or flower buds sprouted where nothing had grown before — on the gravel path that I knew had been sprayed with herbicide by previous gardeners. After three years of leaving this area herbicide-free, a small community of pioneering wild plants has sprung up — some clearly identifiable as being leguminous. I imagine they are actively building up fertility underneath. It is amazing how Nature provides precisely what the soil needs. Before you pull out a weed, try to examine it closely. You may be pulling out a real treasure that has the potential to enhance the fertility of your soil.