While it is nice to have all these direct benefits for the soil around the yard and gardens, the primary reason for using compost is to reap the indirect benefits in terms of healthier, more colorful, more productive plants. Let's take a brief look at how the compost added to the soil ultimately yields sturdy, happier plants throughout the landscape.
General health improved - A soil laced with sufficient humus or compost (3-5%) fosters a moderate but steady rate of root growth for most plants. There is a consistent supply of sufficient water, air, and nutrients over time so the plant grows steadily rather than in spurts. A soil low in organic material that offers a dose of fast acting nitrogen fertilizer stimulates a surge in plant growth for a few weeks which inevitably abruptly tapers off as the nutrient fix is depleted, a situation common to many lawns being fertilized with liquid fertilizers. Plants are left to cope with reduced levels of essential nutrients until the next dose of fertilizer is administered. This on-again off-again growth pattern takes its toll on plants, the stress of intermittent deprivation causing them to fall short of their best performance. It also makes them more vulnerable to insects and disease. Compost in the soil promotes their health by providing consistent nutrition, thereby eliminating stress.
Similarly, soil with sufficient (3-5%) compost will be able to offer a consistent supply of moisture over time for the plants to absorb. They are therefore better able to withstand drought conditions. If it doesn't rain for a few weeks their growth is not retarded by lack of water, because humus, in the form of compost, holds water available to their roots. As with the nutrients, the stressful situation of fluctuating water supply in soil incapable of storing much water leaves the plants drowning on one day and thirsting on the next and it takes its toll on their health and vigor. Plants that enjoy a consistent availability of water which they absorb according to their particular needs are always healthier plants. In addition, because the soil with adequate humus conserves water, the plants will not need to be watered so often during dry periods. This saves your time and energy.