In the last newsletter, I described the technique that I use for my tomato seedlings - basically, seeding crimson clover in the area where the tomato seedlings will be transplanted 3-4 weeks later. Then, clearing off the clover plants in about a one-foot circle where each tomato is set.
This accomplishes at least three important biology-based benefits:
- The presence of the clover roots triggers mycorrhizal fungi and other beneficial microorganisms to come out of their dormant states. The fungi spores only respond to a chemical signal from a growing root nearby, so using the clover to "wake 'em up" gets the valuable soil organisms activated while the tomato seedlings are still being grown indoors.
- When the small circles are cleared and the tomato plants are set out, the mycorrhizal fungi will almost immediately attach to the tomato roots and add them to the food network of the clover, thereby providing nitrogen and other nutrients to the "new members of the colony." As described in earlier newsletters, the fungi serve as a conduit to share nutrients as-needed between the plants in their network.
- Finally, when I cut off the rest of the clover plants at bloom stage (I'd rather they not re-seed by themselves), there will be several pounds of clover roots going deep into the soil. These decaying roots will add considerable organic matter to loosen the soil, retain moisture, and provide fodder for earthworms. While most bare garden soil becomes hard during the growing season, the soil that is filled with clover roots and mycorrhizal fungi will remain more like good potting soil. Meanwhile, after the clover tops are removed the tomatoes continue to enjoy all the benefits of having mycorrhizae on their roots.
There is one very important point that needs to be understood by anyone using this companion-plant method. When the tomato transplants are first set out, they will not look very healthy right away. It takes several days for the mycorrhizal fungi to attach and begin nourishing them, during which time the tomato leaves will show purple undersides - the classic sign of lacking phosphorus. There will also be very little growth, if any.
I've had many nervous customers call and ask if they should give their plants a drenching of liquid fertilizer because they are so obviously stressed. The answer is, "No ,no, no!" - unnatural doses of fast-acting plant food will indeed make the seedlings look healthier, but will disrupt the powerful soil biosystem they are trying to promote.
Within a couple weeks of setting out my seedlings, I can almost tell the exact day when the full root colonization takes place. The purple leaves suddenly turn a vibrant green underneath, growth takes off (with considerably thicker stems than chemically fed plants), and no further fertilization is needed for the season.
I do blend small amounts of dry organic fertilizer and mycorrhizal inoculant into the top couple inches of soil before seeding the clover, but I never rototill or dig my soil very deep, as that can destroy all the earthworm tunnels. This "working from the top" approach simulates the natural process of recycling leaf litter and keeps the soil looser. Rototilling does give a quick fluff, but this effect is temporary and also does a lot of damage to important soil habitat - like a tornado destroying a town above ground. Limiting the depth of tillage and using living mulches (like the clover) are excellent strategies for improving soil health and gaining maximum plant performance.
Note that this general advice applies to both large farms and small gardens. And be patient with your young plants - give the little plant tenders in the soil time to adopt and begin caring for them.
Cheers, and good growing,