Garden Calendar: Compost needs vary from garden to garden


Stephanie Thomas, of Spring Creek Farm, right, and Audrey Coleman, Lawrence, cover onion plants with compost.

Gardeners often tout the benefits of compost, but they rarely mention whether you should use cotton burr compost, manure or the stuff you make in your backyard. The reason? Any compost is better than no compost, although there are a few differences between the commercial products.

Compost should not be confused with mulch or soil. Compost is decayed organic matter, with “organic” simply meaning that it comes from a living organism. Soil is formed when rock (inorganic matter) breaks down. Mulch is material used to cover the soil surface and can be organic (wood chips) or inorganic (rock).

Cotton burr compost, mushroom compost, and composted manure from poultry, sheep, and cattle are the most commonly available commercially-produced composts. Here in Lawrence, area residents also have the option of purchasing compost for a minimal fee from the city’s community compost facility. Many gardeners make their own compost as well.

So which is better?

Some researchers say compost users should experiment on their own to determine the best compost for their soil type and the plants they want to grow. Most of the variability between composts occurs in the pH and salt content.

Salt content and pH play a major role in plant growth.

Unfortunately, little research has been done at Kansas State University or any of the other land-grant institutions regarding the differences between composts. The reason comes back to any compost being better than no compost. One private laboratory, Woods End Research Laboratory, has done a study comparing forty-two different composts, including ten samples from home composting sites.

Wood’s End agrees that the compost user has to decide what is best for their individual needs. However, in their study there was much less variability in homemade compost than in the commercially available products. The similarity in home composts is likely because the original materials going into the compost were similar.

If you lack space or time for making compost, you’ll still likely be looking for commercial composts, though. Here’s more information about them:

Cotton burr compost

Cotton burrs are a waste product of the cotton ginning process. Cotton burr compost is sold in different grades (coarse, medium, and fine) and is usually available as regular or acidified. Acidified cotton burr compost contains sulfur, a naturally occurring element that is used to acidify soil. If you have a soil pH higher than seven, sulfur can improve plant growth in many species.

Mushroom compost

Mushroom compost is the leftover stuff that mushrooms were growing on, and there is a lot of variability in this product. Common materials for mushroom compost are hay, straw, poultry litter, cottonseed hulls and other organic materials. Mushroom farmers use different substrates for different species of mushrooms.

Mushroom compost can contain high amounts of soluble salts. Research at Penn State University says mushroom compost is fine for use over turfgrass. If used in landscape beds or gardens, mushroom compost should be mixed into the soil and rainfall will allow the salts to leach away over time.


Poultry manure does have a little more phosphorus than cattle or sheep manure typically and is often used by organic growers to attempt to provide adequate phosphorus to plants when there are known deficiencies. There is little difference in composition or pH of steer, cow, feedlot or dairy cow manure.

Manure from local farmers is fine to use, too, just make sure it is fully composted before applying it to an area where food crops will be grown. Also, I have not seen commercially available horse manure, but I know it is readily available at local farms. Horse manure may contain large quantities of weed seeds.

Worm castings

Worm castings are worm waste and are sometimes referred to as worm manure or vermicast. Considerable variability can occur with this product because the it also depends on what the worms were eating. In some commercial production, worms may be feeding on high salt content sewage sludge. Like mushroom compost, use worm castings sparingly until you are sure of the effects.

Compost from the City’s community composting facility – The city compost is similar to a home compost pile, only better managed. This compost is made from yard waste collections. A few years of experience and a screening machine is allowing the city to produce a high quality product at a minimal cost to consumers.

And remember, any compost is better than no compost.

— Jennifer Smith is the Horticulture Extension Agent for K-State Research and Extension in Douglas County. Contact her or an Extension Master Gardener with your gardening questions at 843-7058.


Use the comment form below to begin a discussion about this content.

Commenting has been disabled for this item.