There is no question that grow bags are extremely useful for growing tomatoes.
However, in our efforts to stop moisture evaporating too quickly and grow bags drying out, it is still very important to make sure that we don’t prevent good drainage so that there is little chance of “pooling”.
Pooling happens when an area at the bottom of a grow bag retains water and the water can’t escape. This may be because an area of the underside is slightly lower than the lowest drainage hole, or the bag is placed on an uneven surface, so water can’t escape and creates a small pool.
A pool of water that has been sitting there for just a few days develops unhealthy bacteria that can attack roots and cause disease.
A pool of water also continues to dissolve minerals from the soil around it. These minerals may build up in strength to the point where they become toxic to the plant roots.
So, if the bad bacteria don’t attack your plant’s roots, a mineral salt build-up may!
How To Avoid Pooling
Make sure that drainage holes are at the lowest levels of a grow bag.
Grow bag trays without drainage holes may do more harm than good.
One sign that plants may be affected by root attack or mineral build-up is curling leaves at the top of plants.
It’s quite normal for tomato plants to curl their leaves on the lower leaf branches. However, curling leaves on the upper part of a plant often indicates stress.
How To Rectify The Situation
The soil needs a good flush through to clean out the unfriendly bacteria in the pooling area and remove the mineral salt build-up.
My preferred method is with warm water (not hot) containing a wetting agent poured into the grow bag to flush it through. I would use about 20ltr – 4 or 5 gallons.
Make sure that plenty of water comes out of the drainage holes and the bottom of the bag is flat.
We are going to leach (lose) some of the good nutrients like nitrogen etc. but we will just have to feed the soil again when it dries-out slightly. At least our plants will have had the risk of disease and toxic content reduced and be healthier for it.
If you do have to make small holes in your grow bag trays for drainage, you can always seal them again with silicone sealant – fish tank glue.
Avoiding pockets of dry soil
Water always finds the path of least resistance and sometimes leaves dry areas of soil in grow bags and containers. This is the opposite of pooling!
A wetting agent is a good way to avoid this problem – especially if it contains friendly bacteria such as Essentials Wetter.