Duckweed dying?

[grassroots]

I started growing duckweed about a month and half ago. I had 3/4 of the pool covered, then all of a sudden it started going backwards, till it nearly all died. I thought the problem was no direct sunlight. I put it in a 100 litre container in the full sun, it seemed to stabilise then just rolled over and died. I have some in my guppy ponds that is dark green, with very little growth. What do you think I am doing wrong?
Any ideas will be much appreciated.

[GaryD]

Hi Grassroots,

I've experienced the greatest success with duckweed when it has been in a tank with continuous recirculation.

You can kill duckweed by shading it, by feeding it too hard or if the water in which it is growing becomes too hot.

You can find more information that may be of help in my blog post on duckweed here.

Gary

[Wayne Lenhart]

Gary
I went to your sight and read your post on duckweed. Thanks for sharing. I am still not sure why mine is not doing well at all. I have some in a pan by a window that I add fish tank water as it evaporates, the duck weed is more yellow in this pan, water temp about 70 deg. F. and some in a floating raft tank with constant water flow, under a florissant grow light. It is green but not reproducing very fast if at all. Same water temp.
Wayne L.

[jobney]

From http://www.fao.org/ag/againfo/resour...nts/DW/Dw2.htm

"Vegetative growth in Lemna minor exhibits cycles of senescence and rejuvenation under constant nutrient availability and consistent climatic conditions (Ashbey & Wangermann, 1949). Fronds of Lemna have a definite life span, during which, a set number of daughter fronds are produced; each of these daughter fronds is of smaller mass than the one preceding it and its life span is reduced. The size reduction is due to a change in cell numbers. Late daughter fronds also produce fewer daughters than early daughters.

At the same time as a senescence cycle is occurring an apparent rejuvenation cycle, in which the short lived daughter fronds (with half the life span of the early daughters) produce first daughter fronds that are larger than themselves and their daughter fronds are also larger, and this continues until the largest size is produced and senescence starts again. This has repercussions as there will be cyclical growth pattern if the plants are sourced from a single colony and are all the same age. Under natural conditions it is possible to see a mat of duckweeds, apparently wane and explode in growth patterns.

The cyclic nature of a synchronised duckweed mat (i.e. all the same age) could be over at least 1 month as the life span of fronds from early to late daughters can be 33 or 19d respectively with a 3 fold difference in frond rate production (See Wangermann & Ashby, 1950).

The phenomena of cyclical senescence and rejuvenation may cause considerable errors of interpretation in studies that examine, for example, the response of a few plants to differing nutrient sources over short time periods.

In practice this cycle may be responsible for the need to restock many production units after a few weeks of harvesting. In Vietnam, with small growth chambers the duckweed required reseeding every 4-6 weeks (T.R. Preston personal communication) to be able to produce a constant harvestable biomass growing on diluted biogas digestor fluid. There is also the possibility in such systems of a build up in the plant of compounds that eventually become toxic or at least diminish their growth rate."

[qommunity]

Hi, Wayne!

When my duckweed crop slowly dwindles, I make it a point to add a bit more than usual tilapia sludge (aerated/mineralized for at least 1 day).

About the only time I experienced rapidly dying duckweed was when they "cooked off" 2 summers back.
When this was happening, I noticed that the leaves of the duckweed were slightly more yellow where they were shaded. (yes, there were some leaves with clear lines of green/yellow when the shade was steady at only parts of the leaf). I transferred the duckweed tank location to one that gets less sun, and they have been OK since.

You mentioned "water temp about 70 deg.", is the thermometer at the upper water level?

Hope this helps.

[Wayne Lenhart]

Hi qommunity,

You mentioned "water temp about 70 deg.", is the thermometer at the upper water level?

Yes it is.

The sun light thing could be part of it, though it is not too hot because it is in the house. Dose any one know how many hours of light it should have. I do recall some did rather well that I had in a bucket which got very little light, just house light some times, and no sun light.
Wayne L.