The ABC's of Almond Agaricus: A Warm Weather Mushroom, Superlative in Any Garden

 by Mary Ellen Kozak


Almond Agaricus (Almonds) are sweet, fragrant summer mushrooms that can be grown outdoors in the garden. A cousin to the white button mushroom, crimini and portabella, it is much easier to grow. Just like button mushrooms, it grows in compost, but does not require pasteurization, caves or grow houses. Anyone who has a garden... flower, vegetable, shade, or container, can grow this mushroom. You don't necessarily need to plant them with vegetables or flowers, but plants help create necessary shade and harness humidity for perfect mushroom development when they are planted side by side. Grown together, there is also the mutual benefit from the CO2/O2 gas generated and exchanged by both plant and fungus, and the plants appreciate the released nutrients from the compost.

Almonds can be cultivated commercially (and in larger scale) in beds within high tunnels and greenhouses or in areas outdoors where moisture can be added and monitored. It can grow in the shaded woods and sunny garden (best alongside big, leafy plants because of the added shade). Or, it can be grown "small scale" in window boxes and large potted plants, indoors or out. It can be planted May until early July in the north, earlier in the south, or whenever the last frost date is in your area. It is best to plant them so you can get at least 2-4 months of frost-free weather. Almond mycelium can actually survive some freezing weather, but developing baby mushrooms will not, so it's best to pack in as much growing season as possible.

Almonds can be grown in abundance during the warm months of summer.

Almond Cultivation in 6 Steps:

1. Gather supplies

2. Find a site for the bed

3. Build the bed

4. Inoculate

5. Mulch and maintain

6. Harvest and enjoy!

1. Supplies: 

Spawn, compost (bagged or homemade), and a watering can or hose with spray nozzle. You will also want a mulch material to help maintain adequate moisture throughout the growing medium profile. For spawn rates, see Step 4 below.

2. Site preparation and shade requirements:

Choose a location for your Almond bed. The shade requirement for Almonds are related to the ability to keep the bed moist during spawn run, and humidity to encourage large and succulent mushrooms when they fruit.  This can be done outdoors in a fully sunny garden if you can provide lots of mulch and frequent, light watering from a sprinkler or soaker hose over the Almond bed for its spawn run phase, and big leafy plants nearby to capture humidity for its fruiting stage. Chard, lettuces, zucchini, tomatoes and other large leafed vegetables are all suitable companions for Almonds. 

These Almonds are growing in a bed of leeks that are planted in a shallow trench of compost, mulched with straw. Leeks, while loving the compost, do not provide enough shade for premium yields. Tomatoes and zucchini are a better choice.

We have taken to growing all our tomatoes in a high tunnel, and it turns out to be a really good location for Almond production as well. We live north of the 45 degree parallel, so the extra heat and extended season provided by the greenhouse plus the daily attention to plants and soil alike make for a great spot to grow Almonds. We also plant beds constructed in the garden or forest, but yields are frequently lower because the bed is more likely to dry out due to our own negligence. 

3. Choose your compost and construct bed:

Almonds fungally fall at the bottom in the rot chain. While mushrooms like Shiitake and Oyster must have undecomposed lignin and cellulose found in just-cut trees and other woody substrates, Almonds like rich, decomposed plant matter, further down the decay chain. As mushroom growers, we use both spent and composted Shiitake (sawdust) blocks and myceliated, composted Oyster mushroom straw; a dual "waste" substrate. It's pretty cool that you can grow two different mushrooms from the same substrate, just utilizing the food from different levels of decay. You can also use kitchen/garden waste compost, bagged composts and worm castings. We are still working with leaf-based mulch/compost but cannot yet recommend it.

If you are using bulk or homemade compost, take the time to make sure the compost is moist enough, which is typically the biggest problem with using homemade compost. Use the "squeeze test": grab a handful and squeeze as hard as you can. One or two drops of water should want to drip away. The compost does not have to be perfectly crumbly and finished, but you should aim for it to get this way.

Composted straw, kitchen and garden refuse 

Bed construction: We have tested several bed depths and spawn rates and have determined that beds 5 inches deep inoculated at a 5% rate (5 lbs. of spawn to 100 lbs. of compost) is optimal. Make attention to bed depth your priority. Deeper beds (but not too deep for the companion plants) are easier to maintain moisture, and shallower beds are prone to excessive drying requiring more constant watering.

* Note - Choose the right companion plant: It's important to remember that compost is also considered a fertilizer and that too much might not be a good thing for some plants you may be considering to pair with your mushroom growing. Some of the nutrients are being used by the mushroom mycelium, so we honestly have never had too much leafy growth from our tomatoes even when planted into an extra thick compost bed. However, we are a little more reluctant to pair with plants like peppers which have a finicky reputation in regard to an overly rich soil.


4. Inoculation:

After the bed is laid out (if polyculturing, we plant our transplants first and build the bed around them), it's time to inoculate. Spawn rates: You will need about 10 lbs. compost per sq. ft. of bed space that is 5 inches deep seeded (inoculated) at a rate of 1/2 lb. spawn per sq. ft. A standard garden bed 3 ft. wide and 10 ft. long requires about 15 lbs. of Almond spawn. Open the spawn bag and break off egg-sized pieces of spawn and bury on 6-8 inch centers apart in a grid pattern, making sure spawn is covered with some compost after inoculation (take a moment to enjoy the signature almond-ish fragrance of the Almond spawn). Placing the spawn at different depths is also a helpful strategy.

This simple polyhouse is constructed from an "instant garage" frame and greenhouse plastic. The bed to the left has been planted and mulched with straw, the center bed is being inoculated, and the bed to the right awaits planting.

5. Mulching and spawn run

Keeping the bed moist is perhaps the biggest challenge - you will want to keep it damp to the very top of the compost. We have used straw, paper grain sacks, shredded office paper and cardboard to try to hold in moisture without excessive watering. The best so solution so far is cardboard kept moist by a soaker hose laid on top. Daily light sprinkling underneath dry cardboard or paper is almost daily work but is also quite effective. Leafy shade from the plant canopy really helps, even when the plants are young. This year we will be installing a small irrigation system which should give us effective, automatic coverage.

If you can get your cardboard to stay wet, the spawn run underneath will be excellent.

When long strands of mycelium start to knot, fruiting is at hand.

Paper seed bags weighed down with a straw mulch are pulled back to show myceliated compost two weeks after inoculation. Growth is not as strong at the very top as it is when using cardboard, but we are happy with the results.

After 2-3 weeks, watch the beds closely. The mycelium will start to knot just prior to fruiting, indicating that mushrooms are on the way. Now is the time, as an option, to apply a casing layer (preferably just before this stage, as the compost starts to show 60 percent myceliation as shown in the photo above). A casing layer is just a nutrient poor, thin layer of a water holding material that helps increase yields. Adding this layer is OPTIONAL. You will get plenty of mushrooms without it and it is an extra step. To get the most out of your planting though, application of this layer is helpful for maintaining bed moisture and reducing the need for constant watering. We make our casing out of peat moss and adjust the pH with a little hydrated lime (found at garden centers). We often skip the casing stage because fruiting happens faster than we expected and once fruiting occurs, we feel we have missed the window of opportunity, and we are happy with the yields even without it!

Casing recipe:

 3 lb. peat moss

 3 qt. water 

 1 1/2 T hydrated lime (look for types with less than 1% Mg (Magnesium) like Hi-Yield)

Mix well.

The mixture is spread out over the top of the bed, about 1/2" deep. Cover with mulch again and wait for the spawn to grow up through the extra layer, usually 7-10 additional days. Once the mycelium, showing at the top of the bed, starts to move from a feathery look to little tiny knots, you will know that you are just days from a mushroom harvest. Keep things moist!

Make sure the casing substrate is good and wet. Grab a handful and squeeze hard and look for  about 10 drips. It should be wetter than the compost!

Whoops! This bed, mulched with shredded office paper, got past us before we could case it! 

After initial knotting, real pins will start to develop which happens withing days.
Even if you are not a mushroom nerd, it is exciting!

6. Harvest:
New flushes will continue every 2-3 weeks. The first flush will produce single, large mushrooms, with later flushes producing smaller mushrooms, but many of them.

First fruitings produce a few but kingly mushrooms

Later fruitings yield mushrooms in abundance

As the mycelium sets pins, you will be able to judge how large the mushrooms will be. We let the large pins develop into a more open mushroom, like a portabella, for stuffing or grilling use. Smaller pins are harvested closer to buttons as they store longer and transport easily.

Harvesting when the mushrooms are button or cup shape makes for a good quality market mushroom.

From this point, keep the bed reasonably moist until freeze up. Expect mushrooms every few weeks after a good rain or heavy sprinkling from your garden hose.

Keeping a good thing going:
Now that you have used all your finished compost up for the growing season, it is time to start building a new pile. Make sure to add all your trimings or old mushrooms from the Almonds as they will have important bacteria that enhance fruiting attached to the bits of soil from the "rootlets."

Mushroom roots and pieces should go in the compost pile for next years' Almond planting.

Container plantings:

Almonds can grow very well in window boxes or large plant pots filled with basic potting soil mixes, but be mindful of the exposure where the pot will rest and the plant variety. North side exposures are best because the risk of drying out is low. Simply break off tangerine sized pieces of spawn and bury it in the top half of of the container. Use a 7-10 percent inoculation rate: #3/4-1 lb. of spawn for every 10 lbs. of potting soil and a couple scoops of garden soil to add to the bacterial mix. If you are using soil-less potting soil, add 1/3 by weight compost. No special watering is necessary as containers are often watered quite regularly. Shaded containers maintain moisture the best, of course.

A northern exposure on this window box brings nice surprises. Make sure you can open your window for the harvest!

                                                             
Medicinal benefits:

One can't talk about the Almond without mentioning its contribution to the family medicine chest. This mushroom has the more than its share of names: Agaricus blazei, Agaricus brazilienses, The Royal Sun mushroom, and Almond Portabella, although Agaricus subrufescens is the oldest and least controversial, so we'll stick with that. Nevertheless, we believe the fruits of all mushroom cultivation should also be part of the family "pleasure" chest.