How To Find High Quality Compost

The True Cost Of Compost Making

I hear from many gardeners who feel frustrated by the high cost and uneven quality of commercial compost. How can compost of the same brand, from the same supplier, vary so much in quality? Perhaps a bit of background on the art and science of composting will be helpful.

For starters, the texture and appearance of the finished product alters as raw or stock materials change seasonally. Compost based on grass clippings looks, feels, and smells different than compost based on woody and dried plant material mixed with less nitrogen-rich feed stocks.

Seasonal Composts Reflect Seasonal Changes

Seasonal variations may also affect compost, particularly in wet years, when it’s hard not to produce a heavy, dense product. In drought years, it’s challenging to keep compost adequately damp, especially after it moves from the source company to holding areas in supplier’s yards.

Though reputable suppliers may try to keep stored compost evenly damp by spraying their heaps in hot weather, adding too much water without aerating a huge compost heap can result in a soggy bottom of the pile. This anaerobic material won’t hurt the garden but it may smell funky. To restore it fast, spray smelly compost with an aerobically brewed compost tea, which will repopulate it with beneficial biota. These fresh teas are widely available at local nurseries throughout the Northwest.

How Good Compost Is Made

Because compost is essentially a lively product, full of living organisms, it can vary batch to batch even when producers try their best to create a consistent product. Thus, the most responsible compost makers test their end product frequently. For instance, at Emu Topsoil, at Purdy Topsoil, and at Seattle’s Cedar Grove facility, incoming feed stock material is shredded and mixed and tested for clopyralid, ph, moisture content, and the carbon-to-nitrogen ratio before the composting process even starts. After 60 days of composting, the material is screened and tested again. At this point, a bioassay (growing peas and green beans) tests for clopyralid (a persistent herbicide) and weed seed content.

After an additional 9 months of composting, the material is again tested for clopyralid, heavy metals, and other compounds, as well as ph, nitrogen, organic content and what’s called ‘sharps’ (pieces of plastic, glass, etc.). Monthly tests are done for pathogens like E. coli and salmonella, while pesticide residues are tested for on a quarterly basis.

It’s The Law

Since February 10th of 2004, all commercial compost made in Washington must be regularly tested for heavy metals, fecal coliform, salmonella, sharps, nitrogen, and stability. Stability describes the maturation of compost. Less mature compost is very hot and lively, full of degraders that can harm plant roots. Finished compost must be well under 120 degrees and free from heat loving microbes.

Ammonia tests can indicate immaturity (high ammonia levels), though low ammonia ratings also occur when feed stocks are low in nitrogen.  As ammonia converts to nitrogen, the compost becomes more stable and ready to feed plants.

What Does It Mean?

When this testing was first proposed, I asked Jerry Bartlett, then Cedar Grove’s General Manager, if it would mean that Cedar Grove could guarantee that you’d never get a stinky, wet, or dry batch. “Unfortunately, probably not,” he replied. However, Cedar Grove did go on to develop a stringent certification program for the suppliers who sell Cedar Grove compost to the public.

Cedar Grove is also one of the few companies that backs up its compost completely. Over the years, Cedar Grove has done everything possible to make things right for the end customer, which is one reason they are so highly and frequently recommended.

What’s Your Role?

To ensure that your money is well spent, ask the supplier you use to evaluate the condition of the compost they have on hand. Better yet, stop in and look at it yourself. Smell the compost. Feel the compost for texture and tilth. Look at the compost to evaluate texture and particle size, then look at your hands (if they are colored black, the compost may be dyed to improve its appearance).

You can also request a copy of their current test results. Any company that is producing large quantities of compost for sale to home gardeners should be testing often both for pathogens and for quality. While a company need not test every batch, they should be testing frequently enough to give you a good idea of what you are buying. Last year’s tests are not relevant to what you are purchasing now.

How To Read A Compost Test

If you are more familiar with soil tests, it’s important to know that soil test results will look very different from compost test results. For example, a dissolved salts count of around 8-10 would indicate terrible soil quality, but is average for composts, in which most nutrients are counted as salts.

A few companies, like Cedar Grove, offer handouts that help you understand the meaning behind the numbers. Clearly, it’s best to have no measurable trace of E. coli,  whether you are looking at soil or compost. Test results may vary depending on which lab is being used as well. For example, BBC Labs in Tempe, Arizona can test for the diversity range of the main biotic families from bacteria to fungi.  As in the Olympics, a 10 is the top possible rating. Most composts hover at around 4-6, but a few carefully crafted worm composts may rate an 8 or better.

Liquid Teas For Soil Health

These crafted composts tend to be very expensive and are used in small quantities to inoculate aerobically brewed compost teas. The maritime Northwest is rich in tea brewing companies, from Kitsap Penninsula’s Lawn Jockey and Seattle’s In Harmony Lawn Care to the many independent nurseries that have tea brewers on site. Liquid compost teas are easier to apply than bulk compost, since they can be sprayed at various dilutions over everything from lawn to beds and borders and trees and shrubs.

To be effective, compost teas must be used as quickly as possible on the day you buy them. If they sit around very long, the biota they contain begin to feed on each other, resulting in a few big winners and a lot of losers. Within a day, the tea will have lost a lot of diversity. In a couple of days, only the degraders will be left. That makes old tea a perfect addition to your home compost heap, where it will inoculate your slow cooking compost with faster acting critters.

Where Can I Find It?

On the Kitsap peninsula, both Emu Topsoil and Purdy Topsoil supply top quality compost. These local companies have worked hard to develop a safe, healthy and consistent compost. They’ve earned their solid reputations by standing behind their products. If you aren’t satisfied, they’ll make it right. You may pay a little more for high quality compost, but you get the benefits you pay for. Saving a few bucks can leave you (and your garden) burned in a big way.

Emu Topsoil & Compost
7890 NE Ecology Road
Kingston, WA  98346
(360) 638-0117

Purdy Topsoil & Gravel
Various locations service Hood Canal, Gig Harbor and Tacoma areas
(253) 531-6835