May 01, 2016

Why Use Compost?

May 16, 2022

Rapid City Solid Waste Division Customers:

As part of a continuing quality assurance effort, the Rapid City Solid Waste Division periodically tests the yard waste compost products (including wood chips) to determine the quality of the compost offered for sale.  Recently, as part of that testing, the presence of three herbicides was detected.  The herbicides detected are: Clopyralid, Quinclorac, and MCPP. Since the discovery of these herbicides in our yard waste compost products, more extensive testing is being conducted.

What are these herbicides?

  • Generally speaking, these herbicides target broadleaf plants, and are not harmful to turf grass.
  • Clopyralid is considered a persistent herbicide or PH. Which means that it can be detected anywhere from several months to several years in soils or in compost that was made from vegetation previously treated with the herbicide.

How did these herbicides get into the compost?

  • The Rapid City Solid Waste Division adds only water to the feedstock material from which the compost material is made. Our feedstock includes: tree branches, leaves, grass clippings, animal manures, untreated lumber products, and other organic material.
  • These herbicides are used in our communities. Most likely one or more of our compost feedstock materials was treated with the herbicide, and at some point, delivered to the Solid Waste Facility for processing. Herbicides ARE NOT used as part of the yard waste composting process.

What will happen if I use compost products from the Solid Waste Division?

  • At this point the recommendation is to not use the compost for any application where broad leaf plants (including ornamental plants) will be grown. This includes, but is not limited to, most common garden plants such as tomatoes, potatoes, legumes, lettuce, peppers, etc.

What is the Rapid City Solid Waste Division doing about this?

  • More extensive testing is being conducted, including testing the different feed stocks separately in an effort to narrow down where these herbicides may be coming from. If a particular material is found to be the source of the herbicide, that waste stream will be managed separately to ensure that herbicide residues are kept out of the compost to the greatest extent possible.

What can I, the customer, do to help?

  • Make sure you are not using any of the herbicides listed above on any yard waste material you bring to the Solid Waste Facility.
  • If you do bring in material that may have herbicide residue, please let the Solid Waste Division staff know, so appropriate measures can be taken to segregate the material.

When using any herbicide, please follow all instructions and warnings provided by the manufacturer.

At this time, the Solid Waste Division is still advising that customers do not use these compost products in areas where broad leaf plants will be grown. This includes most common garden plants, ornamental plants and flowers.

At home Bioassay

For residents that are interested in doing an at home bioassay.

First, take a number of random representative samples from throughout the pile of compost. Be sure to get deep inside the pile and mix thoroughly. If there are separate sources of compost, conduct individual assays for each. Prepare three to six small (4 to 5 inch) pots with a 1:1 mix of the compost with commercial potting mix containing fertilizer. Additionally, prepare three to six pots with only the commercial potting mix. Place saucers underneath each pot, or position the pots far enough apart to prevent water running out of the bottom from reaching another pot. Plant three pea or bean seeds in each pot, water, and let them grow two or three weeks. There should be at least three sets of true leaves on the peas or beans.

If the plants in the control pots grow normally and the ones in the pots with compost do not, you can assume the compost is contaminated with an herbicide which will adversely affect sensitive plants. If they all grow normally, it would be reasonable to assume the compost is fine. A similar test can be done with young tomato transplants, but herbicide damage may not appear until the plants first set fruit. Keep in mind these tests will be only as good as the samples you take. It would be better to error on the side of too many samples than too few (at least 20 per pile).


Compost is not a fertilizer. It is a soil amendment. It improves low-quality soils by adding organic matter and nutrients. Increasing orgaic matter in the soil improves soil structure so plants, grassed, trees and vegetables will have a healthier growing media. This allows the root system better access to water and nutrients. Experience has shown that plants that are grown in good soil are healthier and have a greater resistence to diseases and reduce water, fertilizer and pesticide/herbicide needs.

Compost has many valuable applications: lawn, potted plants, tree and shrub planting, gardens, improving soil quality, starter mixes and plant disease suppression.

Proper Use of Compost

1. Garden and flower beds: Spread compost uniformly over the entire area, average depth of one to two inches. Incorporate to a depth of four to eight inches (root zone). Apply starter fertilizer (NPK 15-15-10) with compost only if you are applying two inches of compost. Smooth the surface, plant, then water. NOT RECCOMENDED AT THIS TIME 

2. Turf: Spread compost uniformly over entire area, average depth of one to two inches. Incorporate to a depth of four to 8 inches (root zone). Apply starter fertilizer (NPK 15-15-10) to smooth soil. Remember to water thoroughly after seeding or sodding. If necessary due to hot, dry weather, top-dress newly seeded areas with ¼ inch layer of fine compost (3/8 inch or finer) and water well.

3. Landscape: Spread compost uniformly over the entire area, average depth 2-3 inches immediately after weed removal and planting. Avoid placing up against trunks or stems of any plant material. Water thouroughloy before and after to saturate root zone.

4. Backfill for trees and shrubs: Dig a hole ine inch shallower than the depth of the root ball. And 2-3 times wider than the root ball or the container, The finished planting area should be wider than it’s depth . Set the root ball on undisturbed soil so that the top of the root ball will sit slightly higher than the final grade. No compost or fertilizer should be used at the time of planting. Backfill and firm the soil around the root ball, careful not to have the soil above the root flare on the trunk. Spread compost or wood chips around the tree several inches from the trunk.


Compost should be used as a soil amendment ad well blended into the root zone (first 4-8 inches of soil depth) in the fall. Integrating compost opens up the soil for breathing as well as increasing the ability to retain moisture. When the soil warms in the spring, the essential microbes will thrive and provide nutrients for young plants.

Integrating the compost into the soil  in the fall allows the microbial colonies to accumulate before planting. The compost, soil microbial activity and overall structure will improve with yearly fall applications.

A general purpose lawn starter fertilizer rated 15 (nitrogen) 15 (phosphorus) 10 (potassium, should be incorporated in the soil before planting. The starting fertilizer if applying 2” of compost. Do not apply if you are adding one inch or less.

Compost application per 1,000 square feet

¼ inch layer                 .75 cubic yard              500 lbs                        .25 tons

½ inch layer                 1.5 cubic yards            1000 lbs                       .5 tons

1 inch layer                  3 cubic yards               2000 lbs                       1 ton

2 inch layer                  6 cubic yards               4000 lbs                       2 tons

Compost is a soil additive that creates a nutrient rich environment for all types of gardening. It is appropriate for both food and flower gardening, lawns, bushes, trees and roses.


Compost products available:

3/8 inch yard waste compost $20 per ton.

3/4 inch yard waste compost $15 per ton


Pick up availability

8 a.m. to 4 p.m. Monday through Saturday

Rapid City Landfill

5555 South Highway 79


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