A "well-drained soil" is a common description of the ideal growing condition for many plants. But what does it really mean? Water drains through soil by the earth's gravitational pull; how quickly it drains is determined by the soil type. Clay, loam, and sand are the primary soil classifications. In the Bay Area, clay (also called adobe) is the predominant soil type.

The three soil types are composed of different size soil particles; the space between these particles is called the pore space. Pore space dictates how quickly a soil will drain and how soon the soil will require re-watering. To illustrate the difference in pore space, consider the following: if the pores in clay soil were ping-pong balls, basketballs would represent loamy soil, while hot air-balloons would represent sand.

With heavy clay soils, root rot is a primary cause of plant failure. Particle diversification is critical for better water flow in a clay soil. Diversification can be achieved by adding organic matter at planting time. Use a soil amendment like NSCP, Harvest Supreme or Schultz's Clay Conditioner to create better pore space. Follow the steps in the current How-To section to diagnose your soil's drainage ability. Knowing how your soil drains will allow you to adjust your watering pattern for best results, enabling you to successfully grow a wide range of plants.