Sunday, February 06, 2011

Earthworms kill potted plants

For a long time, I have suspected that earthworms kill potted plants by feeding on their roots. Whenever I cleaned out such pots, I found earthworms in them.

Ever since Charles Darwin wrote of the earthworm in 1881, “It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organised creatures”, few have dared to say anything nasty about earthworms, so I kept my suspicions to myself while trying to figure how I could prove my case.

As a scientist I am aware that to prove cause and effect, I would have to set up a comparison between two potted plants in which everything would have to be identical except that one pot would contain worms while the other would have no worms. However, with just two pots for comparison, the results could be muddled up by unknown variations despite efforts to ensure absolute uniformity. It would be better to enlarge the comparison to say 20 pots per treatment. Comparing 20 pots against 20 would be statistically more robust than 1 against 1. I still had to figure out how to measure plant performance and for how long to run the experiment. Things got so complicated in my mind that the experiment never got done.

Last year, I raised half a dozen seedlings of the rare endemic Malayan witch hazel, Maingaya malayana, in individual pots. The seedlings grew at different rates, which was to be expected since they were raised from seeds and could be expected to be genetically different from each other. I had also not taken the trouble to ensure that the soil was exactly the same in all the pots. Also the pots were in different parts of the garden, under different environments. However, one plant was particularly stunted. I thought this was a genetic dwarf because it did not respond to any of my efforts to get it to grow beyond its first few leaves. Finally when it was clear that the plant was about to die, I tipped the plant out of the pot and found earthworms wriggling in the soil. I threw out the earthworms and repotted the plant. It recovered immediately and produced new leaves. The recovery was so striking that I have no doubt the worms were the cause of the stunting and slow decline of the plant.

For those who still doubt, I can now suggest an easy test. Add earthworms to a pot containing a healthy plant. Watch the plant decline over the next few months, then repot the plant after removing the worms, and see if the plant recovers.

13 comments:

Anonymous said...

Hello, sorry I'm actually hoping to get some info on a worm like creature I keep finding in my house. I have pics if you can help

Autumn Belle said...

I always thought that earthworms are good for the soil. Now, I know why some of my young plants died despite the soil being filled fat earth worms.

You mean the earthworms kill all potted plants or only certain types of plants?

Nurseries sell those tiny purple granular pesticide for killing the snails and slugs in the soil. I notice that if I use these on my ornamental plants, the won't be earthworms or other bugs in the soil. I wonder what is this chemical because I see some people use it on their vege plants too but the seller warns against using it on edibles.

Dr Francis Ng said...

The tiny purple granules are probably furadan. I will write my next blog on this.

Jacqueline said...

Thanks for sharing this insight, it's new to me!
Just to share with you, Dr. that I've just bought Tropical Horticulture & Gardening about a week ago and am so captivated by it. I can't contain my excitement with this awesome book that I've decided to share about it with the whole world at my garden website. A million thanks for this gem of a book!

Dr Francis Ng said...

Thanks very much Jacqueline, for reviewing my book in your website. The cost of getting the book into its final form was absorbed by the Academy of Sciences Malaysia. The MPH got the materials for free and reprinted it as a paperback with just a few corrections. I am so happy that the price has come down so much.

Jacqueline said...

My pleasure really in sharing, Dr.! In fact, I'm lost for words in gratitude for what you've done. We're extremely happy too to have been able to possess this magnificent book at such a great discount. God bless you, Dr.!

r2i said...

Hello,
I've been thinking that earthworms are beneficial for plants. I am shocked to see this blog. I have A very precious plant called curry leaf plant (murraya koenigii). Just few weeks back I added around 5 or 6 matured worms to the 30 gal pot. I am worried about the plant. They don't do well with transplantation. What can I do now? I generally let the top 2 inches of the soil dry out before watering. This is a self watering and no way for the worms to escape I believe. Pls. Advice.

Dr Francis Ng said...

A few earthworms in a large container holding a large well-rooted plant are unlikely to damage the plant. The danger is to young plants in small pots.

Anonymous said...

If you place earthworms into a pot and not provide them enough organic material to feed on in the form of decaying leaves or compost, they will eat whatever they can get to survive, including tender plant roots. Earthworms in pots greatly aerate the soil and provide nutrition in the form of droppings. Just place grass clippings or shredded old leave cuttings on the soil surface in the pots. Please don't blame the earthworms for our own failings!

Yow Chuan said...

Yes, I guess earthworms work like garbage collectors, except that they cannot differentiate between one organic material to the next...so if they are contained in a restricted space, they would have no choice but to feed on the plant's root.

To them, it's just another organic matter, but to the gardener, it's their 'precious'.

Thiruppathy Raja said...

Looks amazing!!!! /I look forward to your feedback /thanks for this man it was very helpful.
Potted Plants

miro said...

the experiment just prove that eartworms are not good for potted plants

Anonymous said...

I usually place several potted plants in my flowerbed, which is full of Virginia Creeper. to add color. I noticed 1 pot with 3 purple petunia's had 1 side which was wilted & dying. I dumped out the soil & found 8 earth worms. I dumped the soil into the garden then re-potted with fresh potting soil. The plants are now perking right up. I will place a brick under the plants from now on!!