This post is based on some recent discussions on the OTG group about how to deal with older soil that seems to be performing poorly after a couple of harvests. Re-potting plants is a common solution used by many gardeners, since it allows for adding nutrients and de-compacting old soil. Others may look to add other nutrients (especially in liquid form) in order to avoid having to spend a lot of time and effort in re-potting.

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We thought it may make sense to try and identify the possible problems and then come up with solutions that may be used to PREVENT or CURE the problem.

(a) Maybe the soil nutrients are depleted? This is possible if you have been growing high food uptake plants in the same pot for a long time without much manuring. More likely if you have been growing fruiting plants (brinjal and tomato come to mind) as these are heavy feeders.

Prevention: Add 3-4 fists full of compost near the roots from time to time (every 3-4 months) and also use liquid manures like panchagavya and compost tea. Also add in some wood ash to get some potash in there.

Cure: Try putting in a new crop that will replenish what the previous plant took out, or has different nutrition needs. Crop rotation is the principle that this is based on and there are enough sources online to give you ideas on which one should follow.

(b) Maybe the soil is too compacted: Compaction is under-rated in terms of the impact that it has on the growth of plants. Aerated soil is necessary – not just desirable. If your soil seems compacted, then you will likely have very slow growth or stunted growth in the plants because the roots don’t get enough air and because the microbe population declines – they contribute by transforming nutrients into a form the plants can absorb.

Prevention: Use mulch to cover your soil and make sure that your soil mix has texturing additives like sand/coco-soil to begin with (and is not to clayey). You can also grow some leguminous “cover crop” within the pot.

Cure: Loosen up the soil with your fingers from time to time (as much as you can) or better yet, see if you can empty out the plant and loosen up the soil before replanting.

(c) Maybe the soil has become “diseased” because of some plant: Some soil borne disease is a possibility due to the development of bacterial, fungal or nematode problems. Nematodes can be diagnosed by checking the roots of the previous plant for knots in the root.

Prevention: While bacterial diseases are not easy to fix – you can try adding some neem cake/powder in the soil. Both fungal and nematode issues can be prevented by avoiding excessive watering at all times (very, very important), the growth of bad fungus can be prevented using Trichoderma Virde (TV) as a soil innoculant and making sure soil is covered with mulch (to keep the TV fungus alive).

Cure: Solarisation seems like the only cure and should only be undertaken in an extreme case. Since the soil is effectively dead after the process and will need to be revived.

(d) (NOT VERIFIED) If your previous plant was root-bound: In short, the problem may be the pot and not the soil, there may be harmful “acid-like” residue on the inside of pots that will damage or kill a plant that is subsequently put in. This is something that we have seen no conclusive documentation of, but the theory of experienced gardeners seems to be that these secretions are intended to “drop the excess roots” since there is no room for them in the pot.

Prevention: Pruning your plants leaves and branches regularly help in “natural dropping” of excessive roots below the soil and ensure that they don’t get root bound (and hence don’t produce the harmful acid-like secretions)

Cure: You should wash the inside of the pot out properly, before “refreshing” the soil (adding organic material like compost, and coco-soil that will make it more neutral). Then you can plant something new in the pot.