Avoid Introducing Nematodes to Potted Plants

Gnarly, distorted roots mean root knot nematodes.

Gnarly, distorted roots mean root knot nematodes.

While planting pansies and some other cool season annuals in pots, planters and in flower beds recently, I was reminded about nematodes. If you are unfamiliar with nematodes, they are microscopic roundworms that live in the soil. Some nematodes are beneficial, and several are plant pests. The bad types feed on roots and other plant tissues, disrupting normal plant functions. One of the worst ones is called root-knot nematode.

I first realized I had nematodes several years ago when I planted tomatoes in what I thought would be great gardening soil, but their growth that year was anemic and yield was very poor. When I pulled them up, their roots were gnarly and distorted – sure signs of root-knot nematodes. That’s when I switched to growing my tomatoes in large containers.

Later, after a poor showing of the upright perennial sedum ‘Autumn Joy’ in a different part of my yard, I found yet again nematodes had done their damage. The roots were so badly infested that they were rotting and it is a wonder the sedums were still (barely) alive. So, any sedums I grow are also now confined to pots with good potting mix.

Pansies don’t seem to be affected by nematodes, so why am I concerned? Because I’m planting pansies in both pots and in the ground. Since nematodes live in soil, it is very easy to transfer them on soil clinging to your gardening tools, as you move from infected to clean, uncontaminated soil. Whether you are growing flowers, perennials, shrubs or vegetables in containers, you should always use a good quality potting mix. The best mixes for containers do not contain yard soil, which is why they are often called soilless mixes. Yard soil can contain nematodes, weed seeds or tubers (like nutsedge), or other pests. Plus yard soil in containers often results in poor drainage problems.

The safest option would be to have 2 separate sets of gardening tools, like trowels or shovels, one for the yard, and one just for pots and containers to prevent cross-contamination. If you don’t have dedicated tools, then be sure to always thoroughly clean all your tools of all soil between gardening locations, including different parts of your yard.

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