Vindicator Logo

Test your soil before composting

Thursday, June 14, 2018

Q. How much compost should I add to my vegetable garden?

Michelle from Poland

A. It depends on your soil test. By completing a soil test, you’ll find out if you need more organic matter. It will tell you the levels of major nutrients and the amount of nitrogen required by certain vegetable crops. The numbers provided by a soil test are the only way to know you are adding the right amount to your vegetable garden.

Compost and manure are some of the best things you can add to the soil in your vegetable garden. Adding them provide both organic matter and nutrients to the soil. Both can help you grow better vegetables and flowers.

The organic matter in compost helps improve clay soils. It helps sandy soils improve their water holding capacity. It can be added throughout the growing season and can be used as a mulch to hold down newspapers to reduce weed emergence during the growing season.

Compost contains valuable nutrients, including the major three – nitrogen, phosphorus and potassium. These are the three numbers you see on a purchased bag of fertilizer. They also contain micronutrients needed by plants in your vegetable garden. Thus, compost needs treated like a fertilizer. When you add too much compost, it can be similar to adding too much fertilizer, resulting in run off and other issues.

Adding raw manure isn’t the best idea this time of year unless it has been fully composted. Making compost involves several weeks of turning and taking temperatures. The process gets the materials hot enough to kill weed seeds and pathogens. Applying fresh manure creates a food-safety concern, so wait until fall to apply it and till it into the soil.

If you obtain manure this time of year, the best use is to add it to your compost pile. Follow generally accepted practices to compost it correctly. Aged manure is not compost and should be treated the same as raw manure.

To determine the amount of compost or manure to add to your garden, check out the steps to determine the correct amount at This factsheet provides lots of great information, including the approximate nutrient values of most manures and compost.

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Call the office plant and pest clinic at 330-533-5538 to submit your questions. Regular clinic hours are 9 a.m. to noon Mondays and Thursdays. You can meet David Sprague, an OSU Extension master gardener volunteer in Mahoning County, at the plant and pest clinic.