(Image credit: Milan Krasula)

Plants thrive in nutrient rich soil, but as they grow they deplete the soil of its nutrients. This means that the soil should be amended each year, but the question is when to add compost to the vegetable garden. Read on to learn when to amend garden soil. 

When to Apply Soil Amendments

Fall is the best time to amend the soil for several reasons. First of all, most plants are done growing until spring, so it is easier to remove debris and work around them. The weather is more conducive for amending the soil than during spring’s wet rains. 

There are fewer gardening chores in the fall than spring, so amending the soil at this time makes sense. Also, adding amendments in the fall time through the winter for the soil to gradually incorporate these nutrients.

Fall Soil Amendments

Before you add anything into the soil it’s best to conduct a soil test to determine what amendments are needed. For example, most plants grow best with a soil pH of 6.0-7.0. If your soil test indicates your soil pH needs to be raised you would amend the soil with agricultural limestone. If the soil is low in magnesium, dolomitic limestone should be added. 

If the soil pH needs to be lowered for acid loving plants, elemental sulfur is the most common amendment. Elemental sulfur interacts slowly within the soil, so fall is definitively the best time to incorporate it. Dig the sulfur down into the soil to a depth of 6 inches (15 cm.).

Other amendments are organic in nature and seek to improve soil by improving drainage, water retention and increase nutrients. 

When to Amend Garden Soil Using Manure

In the case of organic amendments, compost can be dug into the soil at any time, but fresh manure definitely should be added in the fall to allow it to have time to break down. Animal manures often contain microorganisms such as E. coli or Salmonella that are harmful to people. For this reason, always incorporate manure in the fall, allowing more time for detrimental pathogens to die prior to the planting of edible crops. 

To err on the safe side, use only compost or well aged manure that has sat for at least a year in the vegetable garden. If fresh manure is the only option, make sure not to plant within 120 days from amendment of the soil. Also, do not use swine manure which has the highest incidence of pathogens. 

Both aged manure and compost are excellent soil amendments but they contain high levels of phosphorus. For this reason an annual soil test is important to monitor phosphorus buildup in the soil. 

Amy Grant

Amy Grant has been gardening for 30 years and writing for 15. A professional chef and caterer, Amy's area of expertise is culinary gardening.