Do Not Compost!

Some materials spread disease or weeds and should NOT be included in the home compost pile.

Caution – Herbicides in Compost

One of the benefits of composting is that many chemicals degrade during the decomposition process. However, several types of chemical herbicides can withstand composting, and they persist in compost, plant material, and soil for several years.

Homeowners who compost waste from their own yards and from their neighbors are more likely to experience contamination by chemicals registered for home, lawn, and garden use. One of the most common herbicides, 2, 4-D (Weed-Be-Gone) has been found to degrade by 50 percent over about 50 days of composting. Similarly, glyphosphate (Roundup) also degrades over several months. However, a common pesticide found in home products, diazinon, degrades very slowly and will be found near original levels in finished compost.

Although any chemical additive in compost is of concern, products that persist for long periods of time are most harmful. The herbicide pendimethalin, which is available in several home and commercial products (Prowl, Stomp, Stealth, Pendulum, Pentagon, Repose, Hurdle, Pendant, Pendimax) degrades so slowly that it is present in high enough levels after composting to damage plants.

Very serious herbicide contamination of compost is more likely when organic material is brought in from commercial landscapes, golf courses, and farms or stables. Herbicides approved for these settings that create special problems for composters include picloram, clopyralid and aminopyralid
(Milestone, Stinger, Grazon, Forefront) . These three chemicals have been shown to persist in soil, plant material, and compost for several years. They are used to control broadleaf weeds, but unfortunately, most garden plants are also broadleaved.

To ensure that chemical contaminants don’t enter the compost stream, conduct a simple test on a trial set of sensitive plants such as beans, peas, or tomatoes. See the resources list at the end of this section for information on home testing for herbicides in compost and mulch.

As new chemicals and crops genetically-modified for herbicide tolerance come onto the market, the water utility can serve the community by keeping up-to-date information available through websites, literature, and public meetings. Consumers can then make informed choices about herbicide use and will be aware that compost materials brought in from outside locations may introduce unknown chemicals into the home landscape.