Drying Duckweed Sustainably
Got a surplus of harvested duckweed and want to preserve it by drying?
Dried duckweed is great for feeding to animals, fish, or as a soil conditioner. As duckweed is roughly 94% water, conventional means of drying involving electricity or gas are energy intensive and not sustainable. Solar drying works quite well and is easily accomplished with equipment you just might have around the house.
I recommend harvesting duckweed early in the morning so as to have an entire day to dry it. Rinse it with clean water and then follow one of the methods described below.
To start with, yes, you can dry duckweed in your kitchen oven, set on “warm” for a few hours. It might not be sustainable, but in a pinch, this works. Just be prepared for your home to smell like a hay barn!
Solar drying can be nothing more elaborate than taking an old aluminum framed window screen and dipping under a section of rinsed, floating duckweed, lifting straight up and laying on the grass in a sunny location. It will take one to two days to dry, depending on how thick a layer of duckweed you’ve got.
Smaller varieties like Wolffia will shrink during the drying process and fall through the screen. To prevent loss, place the screen over a catch basin, such as a bird water bath or cotton cloth. Gusts of wind can blow away dried duckweed, so anticipate this by drying yours in a sunny, wind-protected area.
When drying a gallon or more of fresh duckweed, try taking a section of thin, porous black mulch mat and unroll it on grass or pavement in full or semi-shade. Note: I usually don’t recommend black plastic as it won’t allow water to drain through, but try it if you like.
Harvest and rinse your duckweed, draining it well and gently spread over the surface of the mat to a depth of 1/2 inch . Then take a stick or rake and make windrows to allow for greater surface area of evaporation. After a few hours in the sun, “turn” your windrows and continue to let the heat from the black mat and sunlight finish the drying process. If the weather ceases to cooperate, you can carefully roll up the mat with the duckweed still in it and resume drying on the next day.
Another effective way to dry duckweed is by combining solar heat with moving air. If you’ve got a small fan and solar panel to run it, drape a piece of clear plastic over your mat of duckweed, keeping the plastic close to the duckweed without touching it, supported by 2×4’s running parallel to the length of your mat. On a sunny day, position your solar fan at one end and let the warm, moist air exit the other end.
Duckweed contains beta carotene that will degrade in sunlight, so the quicker you can dry it with the lowest heat input, the better from a nutritional standpoint.
Once totally dry to where it crumbles between your fingers, store duckweed in an air-tight plastic bag and store away from sunlight. Use to feed your aquarium fish, incorporate in poultry, duck or rabbit mash up to 25% of dry weight, or use as a soil enhancer. Drying duckweed is an enjoyable process and it feels great knowing that you are truly on the road to gardening sustainability!