Getting it to bloom

Why won't my Greater Duckweed bloom? (and how to make it flower)

Also called Greater Duckweed, Common Duckmeat, Giant Duckweed (Spirodela polyrhiza).

More about greater duckweed

About Greater Duckweed

Spirodela polyrhiza · also called Greater Duckweed, Common Duckmeat · flowering

Greater Duckweed is the largest of the common duckweeds, with flat, rounded fronds 3–10 mm across bearing multiple rootlets on the underside. Native to every continent except Antarctica, it rapidly covers still water surfaces, providing shade to limit algae and shelter for invertebrates. An important waterfowl food and natural water-quality indicator.

Plant type: flowering

The reasons greater duckweed isn't blooming

Almost every non-blooming greater duckweed traces back to one of these, roughly in order of how common they are:

Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.
Too much nitrogen feed, driving lush foliage at the expense of flowers (very common with general or lawn feeds).
The plant has not been deadheaded, so it stops flowering once it sets seed.
Irregular watering — drought or waterlogging at the budding stage makes buds abort.
It is still too young or was checked by a transplant and is rebuilding before flowering.

Feeding greater duckweed a high-nitrogen general feed and growing it in too little sun — you get a big leafy plant and almost no flowers.

The fix — how to get greater duckweed to flower

Maximise sun. Give greater duckweed the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers.
Switch the feed. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.
Deadhead regularly. Remove spent flowers often to keep it producing more rather than stopping to set seed.
Water consistently. Keep moisture even through budding and flowering — drought-then-flood swings make buds drop.

Light and feeding do most of the heavy lifting here. Dial in the spot with the light guide for greater duckweed and get the feeding right with the greater duckweed fertilising schedule — the wrong feed (too much nitrogen) is one of the most common silent reasons a healthy plant makes leaves instead of flowers.

Bloom season and what to expect

Greater Duckweed flowers across its growing season (mostly summer) and, kept fed and deadheaded, can bloom for many weeks or right up to frost.

Post-bloom care so it flowers again

Deadhead, keep feeding lightly, and many will rebloom; collect seed from the best plants at the end of the season if you want to grow them again.

For everything else this plant needs day to day, see the full greater duckweed care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Greater Duckweed blooming — frequently asked questions

Why won't my greater duckweed flower?

Greater Duckweed blooms on the season's growth given enough sun, warmth and the right feed — there is no cold or photoperiod trick, just good growing conditions and a bloom-leaning feed. The most common reason it is not happening: Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.

How do I make greater duckweed bloom?

Give greater duckweed the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.

When does greater duckweed normally bloom?