University of Maryland Extension

FAQs - Compost

wheelbarrow filled with compost

Photo from Oregon State University Extension

More composting information
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Frequently Asked Questions              Click on Question to View the Answer

Should I cover the pile or bin?

Should I add soil?  Bioactivators?

Should I attempt to compost pine needles? Oak leaves?  Holly leaves? Walnut leaves?

What happens to weed seeds?  Diseased plants?

Should I compost kitchen scraps?

Should I use treated lumber to construct my compost bin?  

Should I use grass clippings that have been treated with herbicides (weed killers)?  

Why is the pile/bin not heating up?

Why does my compost bin smell so badly?

Where should I place my pile/bin?

Do I have to add materials in layers?

Can I add fertilizer to my compost pile/bin?

Will fabrics compost?

Now that I’ve got it, what do I do with it?

Should I cover the pile or bin?
Covering is not necessary, but it may help control evaporation and conserve nutrients.  Rainfall can be a real benefit during dry periods.

Should I add soil?  Bioactivators?
Soil is not necessary and could compact the pile and displace oxygen.  Bioactivators are not necessary.  To kick-start a newly charged bin, simply add a few shovels full of compost.

Should I attempt to compost pine needles?  Oak leaves?  Holly leaves?  Walnut leaves?
Certainly.  Though, tough pine needles and holly leaves will take longer to breakdown.  Newly shed oak leaves are acidic but will be pH neutral when composted.  Walnut leaves contain little, if any, of the toxin juglone.  (Most of that chemical is produced by walnut roots and remains in the soil.)  The composting process breaks down juglone.

What happens to weed seeds?  Diseased plants?
Even though hot composting will usually kill most weed seeds, one should avoid adding weeds that are in flower or have seed heads.  Many disease pathogens are killed by hot composting, but...when in doubt, leave it out.

Should I compost kitchen scraps?
Many kitchen scraps are welcome additions to your compost pile/bin.  Save vegetable and fruit parings, rinsed egg shells, coffee grounds and filters, tea bags, stale bread, etc.  Be advised, however, some municipalities may have restrictions on the backyard composting of kitchen scraps.  Indoor redworm composting and trench composting are good alternatives for kitchen scraps.

Should I use treated lumber to construct my compost bin?  
It is best to avoid using treated lumber (ACQ or copper azoles) in the fabrication of a compost bin.  Also, avoid adding sawdust from treated lumber to the compost bin/pile.

Should I use grass clippings that have been treated with herbicides (weed killers)?  
Although many herbicides break down within a few weeks or months, some others can survive the composting process and have an adverse effect on plant material.  Leave out any treated grass clippings.

Why is the pile/bin not heating up?
This could be the result of insufficient nitrogen.  Or, the pile/bin could be too wet (inadequate oxygen), or too dry (insufficient moisture).  If too wet, turn the heap to dry it out.  If too dry, add water.  If the moisture is ok, add a nitrogen source. 

Why does my compost bin smell so badly?
This is the result of anaerobic digestion and could be caused by too many nitrogen-rich materials (lots of matted grass clippings) or too much water.  Turn the pile and add some shredded newspaper, straw, or sawdust to dry it out. 

Where should I place my pile/bin?
The microbes don’t really care.  Make yourself comfortable.  In full sun, you may have to add water more frequently.  In shade, you may have to share the nutrients with the nearby plants as their roots invade the pile.  Avoid placing bins next to wooden structures - moisture can attract termites. 

Do I have to add materials in layers?
No.  It works, but it is better to mix the ingredients thoroughly.  Layering is often suggested since it requires less labor.

Can I add fertilizer to my compost pile/bin?
Yes, but don’t rely on inorganic fertilizer as your sole source of nitrogen.  Organic sources include blood meal or dried blood, cottonseed meal, alfalfa meal, even nitrate of soda.

Will fabrics compost?
Yes, but avoid wool.  Animal products tend to break down anaerobically.  Cotton is an excellent source of carbon, so don’t hesitate to add old tee shirts, or other discarded 100% cotton fabrics to the compost pile.  Also, don’t forget to add the lint from your clothes dryer.

Now that I’ve got it, what do I do with it?

  • Incorporate it into the soil as a soil amendment.  Add to established beds or when creating beds.
  • Use two inches of compost as mulch around landscape plants to keep the soil cooler, retain moisture, and add nutrients to the plants over the course of the growing season.
  • Grow vegetable and flower transplants and container plants in screened compost.  Try a mixture of 50% compost and 50% commercial soil less growing media.
  • Use it to make compost tea, which has multiple benefits to plants and soil. Applying it to the soil around plants or spraying it on foliage applies beneficial microbes that could suppress the colonization of disease-causing fungi.  Compost tea also contains small amounts of organic nutrients necessary to the health of plants.  It encourages earthworm activity and will enhance the population of soil microbes.

Please send us a question at Ask the Experts if you have a compost question you would like answered. Digitial photos can be attached to your question.

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