What Type of Plants Can Wood Ash Be Used On?

Shrubs and Trees

• Generally speaking, shrubs and trees should get 1/2 to 1 pound of wood ash per shrub or tree per year. The ash should be sprinkled on the soil around the base of the plants and then raked in to mix it up. Be careful not to pour it in a pile and then leave it, because this will cause a concentration of lime and salt in one place, which can burn plant roots and poison the soil. Check your soil's pH levels before adding the ash. It should never be added to highly alkaline soil.

Vegetable Garden and Lawn

• Most vegetables and lawn grass like a soil pH level that is slightly acidic to neutral -- 6.5 to 7.0 is the preferred range. Applying one 5-gallon bucket per 1,000 square feet of garden or lawn is generally safe, but a soil pH test should determine how much, if any, to use. Exceptions to this rule are blueberries (Vaccinium spp., U.S. Department of Agriculture plant hardiness zones 3 to 7), which prefer acidic soil and would not do well in areas where ash is applied. Wood ash also promotes potato scab, so do not use it where potatoes (Solanum tuberosum) are planted.

Perennial Bulbs and Rhizomes

• While wildflowers will grow almost anywhere with the right amount of sun, the more showy imports need more care. Flowers that grow from bulbs and rhizomes need well-drained soil with a pH level of 6.0 to 7.0. Soil will be acidic where pine bark or manure has been used to amend it and in places where pine trees grow, and wood ash is a good way to neutralize that acidity. It will also add minerals that these plants need, especially calcium for strong stems and potassium, both of which are quickly depleted, especially in acidic soils.

Compost Additive

• Another way to use wood ash is in the compost. The microbes that turn yard waste into soil need a neutral pH level to survive. Wood ash can be used as a lime source at 1 cup per bushel of compost. More can be used to counteract the acidic effects of pine needles and citrus rinds if they are present. Wood ash will also add several other trace minerals to the finished compost. Only use wood ash from untreated and unpainted wood, and leave out ash from cardboard, as these will add toxins to the soil.