What plant nutrients are most commonly needed for fertilizers to supply?
Because nitrogen is naturally low in almost all California soils, additional amounts are needed to ensure optimal plant growth. Nitrogen may not be the only supplement necessary, however. Phosphorus may be low in some highly weathered California soils, which are often reddish and have hardpan or claypan layers in the subsoil. Other soils may be low in available phosphorus because of long-term cropping or because of alkalinity, which makes soil phosphorus unavailable. Phosphorus is relatively immobile in soil. Potassium is not commonly needed in most gardens because California soils naturally contain this element. Iron deficiency is common when acid-loving plants are grown in alkaline soils. Iron deficiency can be corrected by acidifying the soil or using iron fertilizers (iron chelate or iron sulfate) according to package directions. Zinc deficiency may occur in gardens where the surface soil has been removed during building and leveling operations. Soil analysis may help to diagnose a
