Check out this cheap and simple method of growing beneficial fungus—mycorrhizae—and spreading it to your indoor or outdoor cannabis crop. Instead of purchasing a packaged inoculant, you can use naturally occurring fungus from your yard or any forest.

If you’ve ever seed up a chunk of soil where roots grow, you might have noticed how an intricate root system branched out from its main stem. If you look a little closer, you might notice the smallest roots resemble something else, fungus. All plants living in healthy soil develop a relationship, sometimes called an infection, with a fungus called mycorrhiza.

Mycorrhiza grows inside and around the roots of the plant and feeds on the sugars it provides. In turn, the mycorrhiza decomposes organic matter, solubilizes phosphates and delivers the nutrients it scavenges directly to the root. This living fungus is like an extension of the plants own root system. Without mycorrhiza, plants struggle to survive unless provided with all the right nutrients in soluble form, as in the case of hydroponics. Plants grown in soil with mycorrhizae are far more tolerant to extreme temperatures, drought and plant diseases.

To “infect” your plant’s roots with mycorrhizae you can dip your seed or clone in packaged spores, or you can make your own. Cultivating your own mycorrhizae has the advantage of being significantly cheaper, better for the environment and way more fulfilling.

To cultivate mycorrhiza find a natural place with relatively untouched soil. Eighty percent of vegetation is in symbiosis with mycorrhizae. Find a bush or tree (except pine or oak), and clear about two square feet of vegetation (grasses) under it. Dig down 10 inches deep and save the soil. For an optimal population of mycorrhizae, do this under several trees and/or shrubs for a wider sample.

Mix this soil with one part coir peat, one part vermiculite and one part compost. Don’t add any extra fertilizers or compost; too much additional phosphate from any source prevents mycorrhiza from growing.

Place this soil into a plastic-lined pit (with holes for drainage) or garden pot. You need to plant a combination of grass (maize, sorghum, millet, oats or wheat) or an allium (onion, leek) with a legume, such as alfalfa or clover. Soak the seeds overnight and plant them close together, alternating the two species. Don’t fertilize the soil, only water with a normal schedule as much as the plants need.

After three months, the mycorrhiza colony should be fully developed, and it’s time to harvest. Ten days before you want to harvest, cut the plants right at the stem and stop watering. As the plants die, the fungus goes into reproduction and starts to generate spores. After 10 days, pull up the roots from the old plants, chop them up and mix them back into your soil—your fungus spores are ready!

To take full advantage of the mycorrhizae in the soil, you need to make sure that your target host’s young roots pass through it. If you grow in a pot, put a one-inch layer of this soil under the first inch of normal soil. The new seedling’s roots will grow through this under-layer of fungus-infested soil and become infected with beneficial mycorrhizae. Alternatively, you can plant seeds into handful sizes of fungus soil placed in the ground.

Cannabis plants infected with mycorrhiza fungus require much less phosphate. If you add a fertilizer with too much phosphate, you run the risk of killing the mycorrhizae, which are very phosphate sensitive. Nitrogen-rich fertilizers, like fish hydrolysate in combination with compost, provide more than enough nutrients for the fungus to break down and deliver to you plant.

Don’t miss our previous Grow Hack: No Soil? No Problem!