How Long After Fertilizing Should I Apply Lime?

After the Soil Test

• The old wisdom prevails that you can't know where you're going 'til you know where you are. Lawn and garden professionals stress the importance of getting soil tested before applying either lime or fertilizer to prevent chemical guesswork, which can harm rather than support plants. Soil tests indicate existing pH, which can help you determine whether you need to apply lime and, if so, in what quantities. Tests also indicate the levels of plant nutrients that may need to be augmented by fertilizer.

Lime: On a Soil-Based Schedule

• Although some gardeners routinely scatter a little lime over garden surfaces as a part of their spring chores, lime must be dug into soil to a depth of six inches to create effective changes in the acid/alkaline chemical balance of the soil. Lime, or calcium carbonate, is slow-acting in soil. Although mild changes are noticeable almost immediately after application, deterioration of lime particles and their absorption into soil is a process that can take up to a year to complete. Expedited by water, the effects of changing soil pH by applying lime are long-lasting and may not need to be repeated for several years, after repeated fertilizer applications and leaching have decreased lime's alkaline effects. Soil testing should be repeated to determine whether and how soon soil needs additional lime. When lime is needed, it can be applied at any time of year, including the winter when annuals have died and perennials have gone dormant.

Fertilizer: On a Plant-Based Schedule

• Garden and lawn fertilizers are designed to support the growth of specific plants during their growing seasons. Their three major components, nitrogen (N), phosphorus (P) and potassium (K), address needs for rapid or sustained accessibility to soil nutrients and the cell structures needed to employ photosynthesis. While the net result of repeated fertilizer applications can be the overall acidification of soil, most fertilizers are not designed to make the kinds of long-term, systemic changes in soil pH that can be effected by lime. To obtain those changes from acidifying materials, you must dig large amounts of slow-decaying organic materials, like composted leaves, into soil. Even pelletized or slow-acting fertilizers focus on producing results within a growing season. Fertilizers, therefore, nearly always are applied in spring, for new growth, during the summer, for fruiting and sustained vigor, and only occasionally in the fall.

With a Waiting Period

• Within these varying schedules, it is necessary to schedule one essential gap between applications of lime and fertilizer. When lime is dug freshly into soil and, therefore, active in top layers, the increases it creates in pH causes fertilizer nitrogen to vaporize. Garden experts suggest that the overall loss of nitrogen available to plants can be reduced by using slow-acting fertilizer or making several small applications of fertilizer rather than a single big one. The most effective strategy, however, appears to be waiting three weeks between applications of fertilizer and lime, no matter which precedes the other. In very wet, very dry, or other stressful growing years, plants may benefit from additional doses of fertilizer, but lime should not be added or adjusted unless indicated by a soil test.