Hypsizygus ulmarius

The White Elm Oyster, Hypsizygus ulmarius, is a striking mushroom with a creamy white cap and distinct gills that curve neatly along its stem. Although commonly mistaken for a true oyster mushroom, this species belongs to a separate genus and is characterised by its defined stalk and dense, meaty texture. It originates from temperate forests of the Northern Hemisphere where it typically grows on elm and beech trees. Today, it is valued both for its culinary quality and its role in environmental cleanup.

In the kitchen, White Elm Oysters are admired for their delicate, nutty flavour and firm structure. They retain texture well during cooking, making them ideal for frying, roasting or folding into pasta and risottos. Aside from their culinary versatility, these mushrooms have a growing reputation for their ecological function. They produce enzymes that can break down agricultural chemicals and petroleum products, earning them a place in mycoremediation efforts.

Growing White Elm Oysters at home using our Mushroom System is straightforward and satisfying, containing everything you need:

Inoculated Mushroom Substrate in a Plastic Sleeve and Display Box

Humidity Tent

Sterile Alcohol Swab

Fine Mist Spray Bottle

Before we get started: The initial phase is the colonisation phase, and this groundwork is crucial to your success. Take note of the dates on your Grow System, this gives you the initial inoculation date and the date colonisation should be complete. You will know your system is ready to get growing once the substrate turns white with mycelium growth. If your substrate is already colonised, you can move on to the growing phase. If not, keep your system in the dark at a temperature between 21 and 27°C. This should not take longer than 21 days. 
Do not disturb your mushroom system in this phase, as premature exposure to fresh air and light can trigger early fruiting or dry out the substrate before the mycelium is established.

Once the substrate is fully colonised and is completely white, you can get started. Place your display box on a counter with sufficient light but not direct sunlight. The ideal temperature should be between 13 and 18°C, and the counter should be free of drafts. Remove the perforated window on the front of the box.  Using the sterile swab, wipe the plastic and the blade that you will be using to prevent bacterial contamination. Cut an X approximately 5cm across into the plastic window, being careful not to cut into the substrate. Mist spray the plastic, placing the humidity tent over the box, and mist spray inside it too. 

Increase the humidity around the kit to between 80 and 90%. This can easily be achieved by using the provided humidity tent and regularly misting inside it. Ensure there is adequate airflow by lifting the tent edge regularly or by cutting small ventilation holes in the humidity tent. Natural daylight from a nearby window or a low-wattage lamp for 12 hours daily will help encourage mushroom formation.  Within a few days, you should see small pinheads forming on the surface. Keep the air moist by spraying a fine mist around the kit, but avoid spraying directly onto the mushrooms themselves. If using municipal water, let the water stand for 24 hours to allow the chlorine to break down before using it to spray your mushrooms. With careful attention to these conditions, the first flush will begin to develop and be ready for harvest within one to two weeks.

For ongoing harvests, stagger your systems for a continuous supply. Start the first system, then begin a new one every 10-14 days. After each flush, submerge the substrate block in clean, cold water for 12 to 24 hours to rehydrate the substrate. Return the kit to fruiting conditions to trigger the next cycle. Most systems will produce two or three good flushes, with each cycle arriving around two to three weeks apart.

In South Africa, plan your growing season from March through October for optimal results, harvesting as the caps flatten slightly and maintaining consistent care to enjoy a productive and delicious harvest.