Gardens: Mychorrizal production bed
Mychorrizas are a type of fungus which form a symbiotic relationship with many plants. The fungi partly live inside the plant’s roots and partly in the soil. The plant provides the fungus with sugars and other products of photosynthesis, and in return the fungus increases the efficiency of the roots by increasing their surface area, apparently up to 1000 times! You can take soil which contains mychorrizas from underneath a well established tree, but as we do not want to have to keep digging around trees we have made a space where we can breed our own mychorrizas. A technique of doing this is by using a ‘trap crop’. Step 1: Dig a pit in the ground (if you only want to produce a small amount you could just use a plant pot). Step 2: Line the pit with plastic to stop too many plant roots going into the surrounding soil. Make some drainage holes in the plastic. Step 3: Dig up some soil from underneath an established tree or shrub (here we used a retama plant) which should contain mychorrizal fungi. Take it from a depth of around 20cm. Step 4: Mix the soil from the tree with the soil you dug from the hole and also with some compost and return this mix to the pit. Step 5: Sow seeds of plant from the legume family (peas, beans, clover, alfalfa etc) and the grass family (corn, millet, grazing rye etc). These two families make relationships with different kinds of mychorrizas. Water regularly. Step 6: Let the plants grow for at least 10 weeks and then cut them down to ground level. Step 7: Wait for a week or so after cutting for the fungi has time to produce spores, then dig up the soil and chop the plant roots into small pieces (5mm should be fine). This mixture of soil and plant roots is your mychorrizal innoculum. Step 8: To use the innoculum, place some in the bottom of your planting hole when transplanting or place some at the bottom of a seed tray if you are sowing seeds.