Solarization : Healing the soil affected by Nematodes

What is Solarization?

The term "Solarizing" may sound fancy, however is nothing but spreading the soil evenly and building up heat in the soil with the help of the sun for about 2 weeks or more.

Why Solarize?

This is for the pest control.

In container gardening, it becomes important to solarize the soil once you are done with one round of crop in that container.

Solarization during the hot summer months can increase soil temperature to levels that kill many disease causing organisms (pathogens), nematodes, and weed seeds and seedlings.

Identification

You may not be able to visually make out seeing the topsoil that it has been affected by nematodes. hence keep a check on the roots when you are done with the crop and uproot the crop. The plant also hints us that it is affected with nematodes, by sudden halt of growth and the leaves withering, and when none of the remedies seem to work, nematodes may be the cause because it has directly affected the roots of the plant! Overall the plant suddenly becomes weak, and perishes.

Nematodes and Nitrogen-fixing nodules are different!

A snippet from here - " The appearance of the galls on the roots can be confused with nitrogen-fixing nodules common in the legume family. However it is easy to distinguish between them, as the nitrogen nodules can be easily rubbed off while the nematode galls cannot be removed. "

Procedure to Solarize

1. Empty the potting mix from a container on a tarpaulin sheet (newspaper would not do until the potting mix is in smaller quantity in balconies; the sheet should be strong and waterproof in case water falls on it, or the pets step on it, the wind may be strong etc) as shown in the below pic.

2. Spread it evenly, breaking it down with gardening tools if required.

3. Separate the roots from the potting mix. 

4. Observe these roots. If they are affected by nematodes , or ants may have layed eggs and would be building a community, as in below pics.

The root at the left is "normal" root, where as at the right is affected by "nematodes" because the roots have knots kind of structure

A closer look of the nematodes affected root.

If the roots are affected with nematodes, solarization of soil is required for 4-6 weeks. If not, 2-3 weeks is good enough.

5. Spread it evenly and irrigate the soil to keep it moist (the heat builds up when the moisture exists) and cover the tarpaulin sheet completely as shown in below picture and keep some weights on the sheet so that it is not affected by the wind. 

6. Wash the container thoroughly (some suggest washing it with bleaching powder and exposing it to direct sunlight for drying, if affected by nematodes)

What after 6 weeks?

After 6 weeks of solarization, add about a handful of neem cake to this potting mix. A handful of Honge cake is also beneficial. It further heals the soil. As a general practice, it is always recommend to add these cakes to the potting mix to prevent such incidents. 

Then for the crop rotation, it is recommended to plant marigold in this potting mix to further heal the soil and after the marigold crop, you could confidently use this potting mix for the next veggie crop.

What if I do not solarize?

Looking at the wait time (6 weeks), it is very easy to get tempted to just discard the affected roots and re-use the potting mix for next crop, without solarizing. But the sad news is that the potting mix is STILL affected and the next crop you put in there will also fail for sure.

Prevention is better than cure

The use of Neem Cake and Honge Cake in the potting mix is for prevention, which should be preached and practiced!