A fast-growing, tiny hit of protein
Duckweed
Protein: 20-40% under ideal growing conditions, often lower if growing in low-nutrient water
Fibre: 15-30%
Methionine: 0.9%
Lysine: 4%
How much to feed: up to 25% of dry matter per day
Where to find it: pet stores that sell fish, in waterways (make sure you identify it correctly and get permission to take it).
There are quite a few types of duckweed around the world. In NZ, there's native duckweed (Lemna minor), and several introduced species.
Duckweed has tiny leaves (3mm-4mm) and free-floats on ponds, lakes, marshes, and slow-flowing water in creeks, forming a solid cover.
It's made up almost entirely of metabolically active tissue, with very little fibre (less than 5% of its biomass) as it doesn't require a stem structure to hold it up (because it floats). That's much less than other high-protein plants such as soya where 50% of its biomass is fibre.
Every part of the plant can absorb nutrients (normally, this is limited to the roots).
Duckweed tissue contains twice the protein, fat, nitrogen, and phosphorus of other vascular plants (plants that circulate fluids like sap). The protein contains a better array of essential amino acids than most vegetable proteins and more closely resembles animal protein.
Growing conditions: it will grow in full sunlight right through to dense shade, and it's very hardy, tolerating water temperatures down to 7°C. It goes dormant if water freezes and then re-emerges when warmer conditions return. It doesn't like wavy water so a growing area needs to be sheltered.
It's also important to have a cover over the growing area to keep the pH level down (6.0-7.0 is ideal) which also helps prevent algae.
Fertiliser: a great place to grow duckweed is in the run-off from a dairy shed or pig or poultry farm as it loves high nitrogen levels. Another option is to collect animal manure, put it in anaerobic water for a few days (in a drum, for example) and then mix or spray that into irrigation water. This assumes you grow duckweed in a pond or a container where fertilising the water will not contaminate a waterway.
Propagation: Experts describe the best method as ‘benign neglect' and regular harvesting. Duckweeds can double their mass in 16-48 hours under optimal nutrient availability, sunlight, and water temperature.
How to harvest it: easily harvested using a skimmer (like you'd use to clean leaves out of a pool). Feed it fresh for optimal nutrition, but you can also store it by drying it out. Anything your hens don't eat can be put into your compost or fed out to pigs, horses, and ruminants (sheep, cattle, goats).
Duckweed loves sucking up nitrogen and phosphates, so it has great potential for cleaning up contaminated waterways too.
Warning: young birds (those under 10 weeks) can't absorb nutrients in duckweed very well so don't feed it to them – use a different source of protein. If you're planning to eat duckweed yourself (see page 57), it needs to be grown in safe, sanitary conditions.
Duckweed is a nutritious option for poultry and other fowl. It also has great promise as a high-protein food for people.