Eradicating PPN with Soil Solarization
Plant parasitic nematodes (PPN) can destroy an entire crop but, as Wiley Geren explains, a patient gardener can use the process of soil solarization to get rid of the harmful nematodes.
Nematodes. More specifically, plant parasitic nematodes, a.k.a. bad nematodes. They’re a common and frustrating problem for home gardens that, unfortunately, can ruin everything you’re growing. The easiest tell-tale sign of this problem can be seen in the roots of your plants, especially if you’re growing a root crop like carrots. PPN feed on the roots of plants, preventing maturity and production of the plant and are easily spotted by the nodules they create on the roots.
There are a few ways to take care of PPN. A popular option for preventing their population growth is to grow French marigold or African marigolds in your garden amongst your vegetables. These flowers contain a natural nematicide. So, if PPN are present, marigold can act as the sacrificial plant for your garden. PPN eat through the roots of the marigolds and the natural nematicide kills them, slowly reducing the PPN population in your garden. This isn’t foolproof, though, since the PPN can still feed on your other crops. Regardless, PPN can be pretty aggressive and may still take over your garden even if you have marigolds, and if that’s the case, soil solarization is your friend.
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What Is Soil Solarization? (It’s easy, but takes time)
Soil solarization is the process of superheating your soil for a prolonged period of time until the PPN die off. It can take a few weeks and requires you to remove everything you’re growing in your garden until just soil remains. While not ideal for the ambitious gardener who doesn’t want to wait, its effectiveness is almost universally agreed upon and allows you to keep your soil instead of replacing it or chemically treating it with a nematicide.
Below is the process of soil solarization:
- Remove all the vegetation from your garden.
- Wet your garden soil thoroughly. In our gardens, we’ll adjust our watering systems to full coverage spraying and run them for about 20 minutes to ensure all the soil is moist.
- Remove your watering systems and anything that will prevent the plastic sheeting (next step) from lying flat on the soil.
- Then encapsulate the soil with a UV resistant plastic sheeting (1-4MM thick) to hold in the moisture. Clear/translucent sheeting has shown to increase soil temperature the most (think greenhouse), but you can use black if that’s your only option and already live in a hot climate.
- Let it sit in the sun for four to six weeks. This allows it to collect radiant heat from the sun’s rays, progressively increasing the temperature of the soil to a point where PPN can’t survive. If you’re in a cooler climate, you may want to wait up to eight weeks.
- After the time has passed, remove the covering and begin planting again!
There is no question that soil solarization can take some time to truly eradicate PPN from your garden, but it is by far the best way to solve the problem if you are willing to be patient and consider what is best for your garden.