Other vineyards have seen improved vine vigor and yield with compost applications. Bob Pestoni of Upper Valley Recycling (St. Helena, CA), producer of Harvest Compost, contracted with Dr. Paul Skinner of Vineyard Investigations to study the effect of his compost on vineyard yields. Skinner compared the effects of compost to a control (no applied soil amendments) in Robert Mondavi Winery’s Tokolon Z block of Cabernet Sauvignon on St. George rootstock.

After three consecutive years, the study at Mondavi found that blocks with compost applied had increased yields of up to 0.9 tons per acre, while the fruit quality remained the same. Application rates for the study ranged from two to eight tons per acre with the 0.9 tons per acre increase in yield occurring in the eight-tons-per-acre treatment.

Cost of the compost at $24 per ton applied at Tokolon was recovered by an increased yield valued at $1,350 per acre. Since the trial ended in 1995, about four tons per acre of compost has been applied annually to 20 acres in Mondavi’s Tokolon vineyard.

In addition to annual applications, Skinner also promotes the use of compost to prepare land for new vineyard plantings. “I typically recommend a pre-plant compost application of five to 20 tons per acre, depending on the results of our “Terrior” soil analysis program. Compost is a good source of trace elements and enhances soil structure,” says Skinner.

Pestoni is in a unique position because, in addition to being a compost producer, he owns Rutherford Grove Winery. When asked what application rate he suggests for compost, Pestoni responds, “You have to know your soil. Work with a soil specialist and get a lab analysis. Then we can talk about application rate.” Upper Valley Recycling does extensive lab analysis on its Harvest Compost and provides potential customers with the results upon request.

Mulch used for erosion control

While many vineyards use straw or cover crops for erosion control, mulch made from urban yard trimmings can be a cost-effective alternative. Mulch is usually used for erosion control, weed suppression, and water retention. Compost improves soil tilth, adds beneficial microorganisms, and may be used as a slow-release source of nutrients. Mulch consists of yard trimmings that are ground and then screened to a uniform particle size. Unlike compost, mulch does not undergo extensive processing to decompose the material and is, therefore, usually less expensive. It is generally applied as a top dressing and slowly decomposes over time.

UC Cooperative Extension advisor Ben Faber in Ventura County has been conducting a demonstration study to examine the effectiveness of mulch and cover crops for erosion control in lemon orchards. “Preliminary results indicate that both mulch and cover crops are effective as weed suppression and erosion control methods,” reports Faber. As vineyards continue to expand onto hillsides, mulch is a feasible tool for erosion control. Vineyard managers may want to experiment with a minimum mulch depth of three inches; if applied at a six-inch depth, the material will likely last for at least two seasons.

Mulch and/or compost effective for vineyard weed control

Clyde Elmore, a UC Cooperative Extension weed advisor, recently spoke at Foothill Grape Day in the Placerville area regarding vineyard floor management. Although he focused on herbicides, Elmore also discussed his research on the use of mulch for weed control. From his trials, Elmore concluded, “Greenwaste wood chips give good weed control. The mulch was persistent in the field and should give long-term weed-control benefits. Because it may last for more than one season, the short-term direct cost is not the best way to evaluate this product.” However, many perennial weeds such as field bindweed are not controlled well with organic mulches. Depending on the coarseness of the mulch, two to six inches of material is needed to control most annual weeds.

At Pina Vineyard Management, White applies compost for weed control in his vineyards. He is perfecting a vine row applicator with the hopes to suppress weeds with compost application right next to the vines. “We find this is the most effective way of applying the compost. The chute will deposit the compost right where we want it and give us a more concentrated application than broadscale spreading.”

Know what you’re getting

Asking questions of compost and mulch producers and reviewing lab analysis results are the only ways to learn exactly what you’re getting. Common ingredients, or feedstocks, for compost and mulch include yard trimmings (collected at city curbs or transported directly from landscapers), manure, and in grapegrowing regions, grape pomace. Any reputable producer will disclose its feedstock. Producers registered with the California Compost Quality Council (CCQC) are required to disclose feedstock, pH, and a number of other product characteristics.

All large-scale producers of compost are subject to composting regulations promulgated by the California Integrated Waste Management Board. Depending on their composting method, these producers are required to maintain the compost pile at a temperature of at least 131° F for a specified number of days. This “time and temperature” process kills pathogens and weed seeds. In addition, regulated producers must test their end product to ensure that certain heavy metals and pathogens are within acceptable limits.

Producers of mulch, which is ground wood chips made from orchard or tree prunings or yard trimmings, are not subject to the regulations and thus are not required to put the material through the “time and temperature” process. However, some producers will subject the material to this process for a minimum time to kill pathogens and weed seeds, but not long enough to fully decompose the material.

Most producers also obtain product analysis which shows NPK, pH, and other characteristics of interest to growers. Martin Mileck of Cold Creek Compost (Ukiah, CA) sells compost to vineyards as a diverse source of nutrients. “I estimate there’s about $60 worth of nutrients in one ton of our compost and it sells for $28 per ton (fob Ukiah, CA), a fraction of that cost,” says Mileck. While nitrogen content of compost varies, depending on the feedstock, Mileck’s product typically has between 1.5% to 2% nitrogen. Mileck also cites the high potash content (about 2.5%) of his product, which results from the addition of wood ash. Wood ash can also be a good source of other micronutrients.

If producers don’t have what you want, ask if they can get it or make it. Material can be screened to specific particle size, small or large. In addition, many producers will make custom blend products upon request. Norm DeLeuze of ZD Wines in Napa Valley wanted a compost higher in nitrogen than the yard-trimming compost normally produced by his supplier for his vineyard in the Carneros district.

Greg Kelly of Napa Garbage Company responded to DeLeuze’s needs by adding manure to the feedstock, increasing the nitrogen from 1.59% to 2.19% and increasing the phosphorus from 0.29% to 1.4%, producing a more balanced, higher quality compost. DeLeuze was satisfied, and Kelly is now selling the new product to other grapegrowers in the area.

To locate a supplier near you in California, call the Waste Board at 916/255-2410 to request the “Compost and Mulch Source List.”

Making your own compost

A number of wineries compost their own pomace which solves a waste management issue and produces a valuable end-product. While some wineries use pomace as the only feedstock, a higher-quality compost may result from adding other feedstocks to the mix of organic materials.Yard trimmings, old animal bedding, and manure are good additions to pomace. These additional feedstocks serve as bulking agents and may help to buffer the pH of the pile. Another option to raise soil pH is to add lime.

Those who make their own compost should be familiar with properly using the basic “turned-windrow” technique. The most common composting problem is failure to turn the windrow (pile) frequently. This causes the pile to become anaerobic and encourages undesirable microorganisms and produces unpleasant odors. The windrow should be kept about as moist as a rung-out damp sponge and turned regularly. The more frequently the pile is turned, the faster the compost will decompose. However, less frequent turning saves labor and energy.

“To obtain sufficient pathogen reduction and to kill weed seeds, a minimum of three turnings is required in the 1-2-3 turnover method,” advises Bakx, who developed the method. Allow five days or more between turnings. Depending on the composition of the material and the particle size, three turnings will result in compost in five to eight months. Turning six to eight times will produce a finished compost in three to five months.

It’s helpful to obtain a compost thermometer and monitor the internal temperature of the pile. The pile should be between 131°F and 150°F for at least 15 days. If the pile exceeds 155°F, turn the pile to dissipate the heat; adding additional water may result in even higher temperatures. Preventing the pile from reaching 160oF helps maintain the desired beneficial microbes and also helps prevent spontaneous combustion from occurring.

While the Waste Board encourages on-farm composting, current composting regulations may govern agricultural composting in certain situations. On-farm composters who use only agricultural commodities (e.g., grape pomace) as feedstock are not subject to regulatory oversight if they sell or give away no more than 2,500 cubic yards of compost annually. If they are mixing non-agricultural source material such as yard trimmings with pomace, on-farm composters may be subject to nominal requirements.

Check with your local enforcement agency (LEA), usually the county environmental health department, for clarification on any requirements before composting any non-agricultural source materials. Look for California Code of Regulations, Title 14, Chapter 3.1. California growers seriously considering on-farm composting may contact this author for more information and request a copy of the On-Farm Composting Handbook.

A beneficial practice to consider

If your vineyard could benefit from improved soil structure, added beneficial microbes, improved moisture retention, and better erosion control, consider making or purchasing compost and mulch. Compost and mulch can be important long-term investments in the health of your vineyard.

Christy Porter promotes the use of compost and mulch in agriculture for the California Integrated Waste Management Board. She specializes in the area of compost use in vineyards and can be reached in her Sacramento office at tel: 916/255-2410 or by e-mail at cporter@ciwmb.ca.gov.