Timing of Lime and Fertilizer Applications

Figuring out when to apply limestone and fertilizer can be confusing.  Here’s a handy guide for application of various amendments.

Limestone

Since limestone can take a long time (4-6 months) to raise soil pH, it’s best to start as soon as possible.  For existing plantings, limestone can be applied twice a year, in the spring and fall.  To avoid damaging existing plantings, limestone applications should be limited to the following:

• 5 lbs. per 100 square feet for gardens, trees, and shrubs
• 50 lbs. per 1,000 square feet for lawns, turf, and commercial nursery crops
• 1 ton per acre for commercial crops

For new garden plots, lawns and other plantings, the entire amount of limestone may be applied at one time.  When applying more than the limited amounts listed above, limestone should be tilled into the soil to a depth of 6 inches.

Soils should be re-tested 4-6 months after the final limestone application to check soil pH. Once your target pH has been reached, soils should be retested every 1 or 2 years.  Do not assume that your soil needs limestone.  It’s entirely possible to raise your soil pH higher than desired!

Fertilizer Blends Containing Nitrogen

Because nitrogen moves freely between the soil, water, and atmosphere, it’s best to spread your fertilizer applications out over the growing season to avoid leaching.  For flower and vegetable gardens, as well as trees and shrubs, fertilizer applications should be made in the spring after the soil warms up, and again in mid-June.  Late applications of nitrogen can spur new growth, which can cause damage in the event of an early frost.

For lawns, most of the fertilizer should be applied in late summer/early fall (September), and late fall (November).  This is when root growth is the greatest.  Avoid heavy applications of nitrogen in the spring and early summer as lush, succulent growth is more susceptible to certain diseases and summer stresses.  A single, light spring application of nitrogen is appropriate early in the growing season.

Bone Meal, Triple-Phosphate, Potash, and Other Amendments

Bone Meal and Triple-Phosphate, which supply phosphorus (as P2O5), and Potash, which supplies potassium (as K2O), may be applied at any time during the growing season.  Since phosphorus and potassium are not subject to leaching, application of these amendments may be made all at once.

 

Do not apply limestone, fertilizer, or organic amendments to very wet or frozen soils.

 

For more information about home lawn and garden maintenance, visit http://ag.umass.edu/resources/home-lawn-garden.