Oysters on Straw

Please note: Blue Dolphin™ and Polar White™ Oyster spawn are log specific strains, and are not recommended in substrate applications. King Oyster and Black Pearl Oyster are only suitable for production on a sterilized sawdust substrate.

Growing Oyster mushrooms on pasteurized straw can be one of the most rewarding production ventures for mushroom growers. With the current emphasis on local foods and local farm markets there is hardly another crop that is so well suited. Oyster mushrooms have a relatively short shelf life and are a bit fragile, so they are best hand carried and sold within a week. When fresh, they are some of the most stunning and colorful produce available, perfect for the market gardener.

Oyster mushrooms can grow on a variety of things including wood logs, cottonseed hulls, corn cobs or office paper, but in North America, cereal straws are the substrate of choice (wheat and oat straw do particularly well). Equipment is fairly simple and outstanding results are obtained relatively quickly. It can be fraught with its own problems as scale-up commences, however, so be prepared to research and proceed carefully as you prepare to increase production.

Straw must be moisturized to host the growth of the mushroom mycelium and treated with hydrated lime or heat. Wood logs do not need such treatment as they are already moist and have a protective sleeve (the bark) slowing moisture loss and providing a semi-sterile environment. In addition, living green trees cut for Oyster cultivation have an active immune system that holds back contaminants.

The Basic Steps for Growing Oysters on Straw

1. Prepare the substrate
Straw must be moisturized to promote the growth of the mushroom mycelium and treated with heat or hydrated lime. Whenever possible, chop the straw into 3-5 inch pieces with a chopper, lawn mower or string trimmer in a garbage can. Heat pasteurization will kill off most organisms that compete directly with the Oyster mushroom mycelium, and will kill any of the cereal grains present in the straw. Chopped straw should be put into pillow cases, grain sacks, or any similar water penetrating bags. Secure the bags with zip ties or string. Heat a large pot of water to 160°F. Submerge the bags of straw completely in the water, weighing down with bricks or similar objects. Cook the bags for 45-60 minutes, all the while monitoring the temperature (compost thermometers work great for this). Ideally, the cooking temperature should remain around 165°F. Five degrees up or down is fine. When complete, drain the standing water, and cool for about 20 hours or until the internal temperature of the straw is below 75°F.

The Cold Soak Method can be used as an alternative to heat pasteurization. Hydrated Lime (also known horticultural hydrated lime) is a powder made by treating lime with heat and pressure. It is available at garden centers (we use Hi-Yield brand). When added to cold water at a rate of about ⅛ cup (12g) per gallon of water, this soaking solution will make the straw a suitable substrate for Oyster mycelial growth. At this rate, the pH level should be up around 12, which is ideal. It is a good idea to invest in pH strips (litmus paper) to assure you are achieving this level. Adjust the given rate as needed. Add the powder to the soak water, then add the straw. Soak for 18-20 hours, and drain for several hours until the moisture content is around 65%. The squeeze test can be used to estimate moisture content. Simply grab a handful of straw and squeeze as hard as you can. No more than one drop of water should come out.

2. Inoculate
Once prepared, the straw can be inoculated (planted). This process should happen indoors in a clean area with minimal traffic. Use 5-10% of the wet weight of the straw in grain or sawdust spawn: a 20 lb. bag of wet straw would need 1 lb. of grain when inoculated at 5%. A 4 lb. bag of our grain spawn will inoculate roughly ⅔ of a small square straw bale when using a 5% rate (filling about 3 or 4 of our 18 x 36 inch Oyster bags). The straw should be emptied from the soaking bag into a large sterilized container; a stainless steel tub sink that has been disinfected works well. Evenly mix in the proper amount of grain spawn with rubber gloves or clean hands. Tightly and as compact as possible, stuff the straw/spawn mix into polyethylene sleeves, buckets or any other suitable container, seal (with zip ties, string, tape etc.) or cap, and label. Alternately, straw and spawn can be layered within sleeves/buckets, skipping the need for mixing first in a sterilized container. If reusing buckets, be sure to clean thoroughly between uses. Holes for circulation and eventual growth should be put in immediately after planting (an arrow broadhead attached to the end of a wooden handle works great for poking perfectly sized holes in poly sleeves). Using a diamond pattern, punch holes about 4-6 inches apart from one another (see diagram to right).

3. Incubate
Place filled sleeves/buckets into incubation. Ideally, the room used for this should be somewhere between 75-77°F with a humidity of 80%. During this period, it is extremely important to monitor internal bag temperatures. These temperatures usually peak after 3-5 days of inoculation, and should not exceed 90°F. Spawn death occurs at 100°F. If temperatures become too high increase air flow, decrease room temperature, or relocate your bags/buckets. Bags/buckets should stay in incubation until pinning occurs, usually within 3-5 weeks.

4. Fruiting and harvesting
Once pinning is visible, the bags/buckets are ready to move into a fruiting room. This room should be cooler in temperature, 65°F is optimal. Humidity should be increased to 85-90%. Make sure the bags/buckets receive plenty of light. Generally, 10-12 hours of natural, incandescent or fluorescent is optimal. However, if growing Golden Oysters, it is important that the light be 600 lux: 2× the intensity of normal lighting. The bags/buckets will fruit many times and can last several months. As the number of fruitings increase, yield and quality will decrease.