Wattles (Acacia sp.) are hard seeded and their seeds survive a long time in the soil. In the bush, they come up in a flurry after fire. For a long time it was thought that the heat from fire cracked the hard seed coat, but a few years ago it was found (in research largely conducted at Kings Park in Perth) that smoke is the key. Smoke triggers the seed to break dormancy and germinate. It’s now relatively easy to find online instructions on how to make smoke water (bubble smoke through water) to pour over seeds or how to use smoke directly to germinate the seeds. But when I germinated the wattle that now grows in front of my house, I used a different method. I simply poured plain boiling water over the seeds and left them for a few hours. The heat cracks the seedcoat enabling the water to penetrate inside the seed and germination to begin. If you use this method to germinate wattle seeds, be sure to plant out the swollen seeds. Ones that fail to swell are unlikely to germinate as the water has not penetrated inside the seed. You can also ‘scarify’ the seed – rub it with sandpaper or something similar to break the seed coat, but this has always seemed to me to be a touch more difficult that simply pouring boiling water over and waiting a few hours. If you rub off too much of the seed coat, you will damage it and destroy the seed; too little and the seed coat won’t be permeable to the water. In the wild (including the wilds of my front verge), a few seeds will be ‘scarified’ by the movement of mulch or soil and will germinate.
But for widespread germination in the bush, fire is the key. An understorey of fire-stimulated species quickly germinates in the blackened landscape. Wattles are a colonising species, quickly covering the ground and providing feed for animals. They also fix nitrogen. Wattles are legumes, that miraculous group of plants with symbiotic relationships with specific soil bacteria. The soil bacteria – rhizobia – form nodules on the plant’s roots. It is the rhizobia, not the plant, that ‘fixes’ nitrogen. there’s a lot of nitrogen in air and rhizobia take this gaseous nitrogen and turn it into organic nitrogen in the nodules, making it available to the plant and other soil life. The plants use this nitrogen to build proteins, and when animals eat the plant, they consume the proteins.
The seeds on the wattle in my garden are, like other legume seeds, high in protein. But my wattle is not one of the few species that are commonly (or perhaps uncommonly) eaten. there are close to 1000 species of wattle in Australia, many of which have very nutritious seeds, and some of which have leaves that are palatable and nutritious for livestock. Unfortunately, my wattle is not one of these species. I wasn’t thinking of wattle seed to add to my baking when I plucked those seeds that day as I walked past; I was only thinking about a cheap way to grow a screening hedge! It worked for that purpose, but perhaps I’ll think a little more broadly when this particular shrub dies off – and that will likely be soon, as wattles are not generally long-lived plants.