By Patty Glenn Leander Contributing Writer

Last year I wrote an article about retired Harris County horticulture agent Bill Adams and his productive kitchen garden and fruit orchard near Brenham (November/December 2008). Bill said his secret to successfully growing edibles is to use plenty of organic matter, and the comment that his favorite amendment is mushroom compost generated much interest among the readers of Texas Gardener magazine. Inquiries from readers about mushroom compost led me to a visit with Darrel McLain, CEO and founder of Kitchen Pride Mushrooms in Gonzales, who invited us for a fascinating tour of the mushroom farm. The cultivation process begins with raw compost materials and ends approximately three months later with beautiful mushrooms packed and ready for shipping to stores across the state, generating tons of spent mushroom compost as a byproduct.

Though we consider mushrooms a vegetable and they are classified as such by the American Dietetic Association, they are not true plants. As you may know, mushrooms are a fungus, and they share their place in the fungi kingdom with their relatives, mold and yeast. But before you turn your nose up at the thought of eating fungus, let me remind you that Roquefort, Camembert, Brie and bleu cheese all get their distinctive flavor from mold; yeast is used in the fermentation process of beer and wine; bacteria give buttermilk, yogurt and sour cream their acidity; and we owe that unmistakable and delectable aroma of rising bread to baker’s yeast. All of these foods bring flavor and substance to a meal. And what goes better with a perfectly grilled steak than a sumptuous side of sautéed mushrooms?

Unlike other agricultural products, mushrooms are grown under scientifically controlled, sanitary conditions and are never touched by human hands, at least not until your own hands unwrap the package. Mushrooms should be stored in the refrigerator and used within 4-5 days. Wash them just before using under cool running water and blot dry before cooking. Mushrooms are a low-fat, low-calorie and cholesterol-free food, and they are a good source of potassium, selenium, riboflavin and niacin. They also contain small amounts of vitamin D, and recent scientific research has shown that when mushrooms are exposed to UVB light for just 5 minutes, their vitamin D content increases significantly. This is good news if you are a mushroom lover because many of us have low levels of vitamin D due to our frequent use of sunscreen and limited time outdoors (vitamin D is produced in our bodies when exposed to sun). Researchers are currently testing the best methods for exposing mushrooms to UV light during the pre- and post-harvest phases, and these vitamin D enhanced mushrooms may one day be available in our local grocery stores.

Because mushrooms have no chlorophyll and cannot produce energy from the sun like true plants, they must live off other plants and plant matter, and composted organic matter is the perfect medium. At Kitchen Pride, this process begins right on the premises with the production of compost that takes place under highly monitored and precise conditions. Truckloads of wheat straw arrive on a weekly basis. Then it is wetted down and thoroughly mixed with cottonseed meal, poultry litter, water and other proprietary ingredients. These piles are watered and turned several times over a five-day period to initiate an accelerated composting process. The mixture is placed into a machine that extrudes 7-foot-tall by 7-foot-wide loaf forms called “ricks.” The ricks are moved to a special bunker with an aerated floor which is controlled by computers that monitor oxygen level and temperature. Here the ricks are flipped twice over a seven day period to maintain favorable composting conditions. After this initial two-week processing, the mixture is turned and reformed into ricks, which are watered as necessary to maintain aeration. After six more days, the ricks are moved into pasteurization rooms. The air in the pasteurization rooms is sent through a HEPA filter, and the temperature is carefully monitored to make sure that the temperature of the compost doesn’t go above 160. After the compost cools down to 133, steam is injected into the room and the compost heats up again to 148. This process of pasteurization kills many harmful pathogens, weeds and insects, but does not kill beneficial microbes that aid in the composting process. The steam is then turned off, and the temperature of the compost falls to 118. (Note: contrary to what many people believe, mushroom compost is pasteurized, not sterilized. The sterilization process, which takes place at 250, would kill everything, including the good microbes.)

By the fifth day, the compost smells sweet and earthy, and it is allowed to cool down to approximately 90 before being inoculated with the Agiricus bisporus culture and transported to long aluminum shelves in the growing rooms. Air temperature and moisture are carefully monitored to create ideal conditions for growth. The culture soon begins to spread out in a thread-like matrix throughout the compost, and when the culture is 13 days old, a 2” layer of peat moss mixed with limestone is added. The peat moss holds moisture and allows the mushrooms to grow up and form tiny pinheads on the surface. During this growth period the mushrooms take up nutrients from the compost. It takes approximately two weeks for the white button mushrooms to reach a mature size; and they are carefully harvested by skilled employees, whose gloved hands efficiently remove the mushrooms, one by one, using a small, sharp knife. The stems are trimmed and the mushrooms are placed in a vacuum cooler where they are quickly chilled to 34°. Then they make their way to the packing room and ultimately to the shipping room.

The first harvest, or bloom, takes two to three days. The growing medium is then watered with a fine mist and the air temperature and humidity are adjusted to encourage a second bloom, which comes about a week later, followed by a third bloom. The harvest at each subsequent bloom is diminished as the mushroom compost is exhausted. After the third bloom, the room is steam pasteurized to kill any pathogens, which also kills any residual mushroom culture, and the growing room is ready for a fresh batch of inoculated compost. Fresh mushrooms are always in season because this process continues 365 days a year.

The spent mushroom compost is sold to landscape companies and individuals as a soil amendment. It is a good source of organic matter but should not be used as a planting medium by itself because the concentration of soluble salts can burn tender plants. It is slightly acidic with a pH of 6.6-6.8, and though the nutrient content varies, the N-P-K range is approximately 0.50-1.50% nitrogen, 0.25-1.00% phosphorus and 0.50-0.75% potassium. The C:N ratio of spent mushroom compost is 13:1, which is ideal for mixing into garden beds. There is nothing magical about mushroom compost, but if you live near a mushroom farm, it is an economical, readily available source of organic matter. As with any other compost, it helps improve the soil structure and moisture-holding capacity of the soil. The addition of organic matter to garden soil increases beneficial microbes and creates a favorable environment for earthworms, both of which help make nutrients available to plants. Mushroom compost can be used as a top-dressing, it can be added to the compost pile or it can be mixed into garden soil. The pungent aroma of fresh mushroom compost belies the clean and sterile conditions under which mushrooms are grown. If you order or pick up a load of mushroom compost that has a strong ammonia odor, it is a good idea to allow it to further break down by letting it sit and cure for a few months before using. If you want to use it right away, till a 3-inch layer into the soil and water well before planting. Watering is especially important; it will help draw the salts through the soil so they do not build up in concentrated amounts.

Much of the spent mushroom compost produced at Kitchen Pride is sold to landscape companies and area farmers, but because mushrooms are grown year-round and the compost process never ceases, there is often plenty for purchase by individuals. Vegetable gardeners go giddy over compost, and I am no exception. Even though it meant I would be faced with the task of toting wheelbarrow loads from the driveway to the backyard on a steamy July day, I felt a rush of exhilaration as I watched my small truck bed being skillfully loaded with mushroom compost.

If you are interested in getting a truckload from Kitchen Pride for your own garden, it is best to contact the front desk at (830) 540-3693 to check on availability. Other landscape supply companies that purchase Kitchen Pride’s compost for resale are:

Keller Materials, San Antonio, (210) 648-4221

Fertile Garden Supply, San Antonio, (210) 688-9435

Sweet Home Sand and Gravel, Yoakum, (361) 293-3677

Jansky’s Sand and Gravel, Hallettsville, (361) 798-5892

The Monterey Mushroom facility in Madisonville is another source for spent mushroom compost. They are located at 5816 Hwy 75 South, Madisonville. The number to contact for availability is (936) 730-3600.

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