Physically breaking up the soil by spading and cultivating creates millions of tiny air pockets in the soil, giving the microorganisms air to breathe and making the soil fluffy. Mulch conserves water and is transformed into humus by the bacteria, fungi, insects and other animals that teem in the top six inches of soil. Mulch acts as an insulating blanket, keeping the soil warmer in winter and cooler in summer. Weeds do not have a chance to get a foothold. Plant Roots contribute astonishing quantities of organic matter and put it directly in the soil.
Roots are also the main agents in making the soil lighter and more open because of their probing.
Bruising or wounding the tomato plant leaf activates a hormone that causes insects attacking the plant to die of severe indigestion. Unbalanced feeding, especially of nitrogen, can increase aphid population and other troublemakers. Buy varieties with built-in resistance to bacterial or viral diseases. One good early spring barrier idea is the cutworm collar. Use a ring of tar paper, cardboard or a tin can with both ends removed, shoved an inch or two down into the soil around tender transplants or seedlings.