Trying to Save Basil
Answered by: Richters Staff
Question from: Jane Malleck
Posted: Before April 1998

I am having problems similar to those described by Mary Halfhill. Unfortunately, almost all my herbs have died! Now the one I have left, my basil has even more problems! I have put it under a plant light and in a southeast window. It has been dropping leaves and getting lighter in colour. Now I notice that it has a white substance on the underside of its leaves. I figure this is the last stage before death!! But I would still like to save it. I sprayed it with Safer’s insecticide last night. Can you suggest a remedy for both the white stuff, the weakness of the plant and the mold that Mary mentioned?

I live in Quebec. Our growing season is very short. I love cooking with fresh herbs, so I am determined to find a way to make them survive the winter!!!

First, to deal with the problem of general failure of your herbs. Here is a troubleshooting guide for future reference:

1. Inadequate light. Most of the popular herbs require strong light. In winter the days are short and the light intensity is low, so plants do not get nearly as much light as they require. This winter (1996-97) has been one of the dullest in recent memory – southern Ontario, for example, got less than half the normal number of sunny days in December. There is not much you can do other than moving your plants to a brighter window or providing supplementary light, which you tried.

2. Pest infestation. Besides the more obvious pests like aphids and whiteflies, herbs are susceptible to spider mites. They are very tiny, barely visible to the naked eye, and can wipe out an indoor garden of herbs in a few weeks. Spider mites thrive in warm, dry environments typical of heated homes in winter. Signs of heavy infestations include a white- or yellow-mottled leaves and spider webs between the leaves and stems. If you examine the undersides of the leaves carefully you will see tiny dust-like specks that move slowly. To control spider mites, dip the entire plant above the soil in a pail filled with insecticidal soap mixed according to the same directions for making the spray. Repeat dippings twice a week for four weeks, or until there is no longer any evidence of mites.

3. Drying out. As obvious as this is it is surprising how many people forget to water or don’t know how to water properly. When plants are growing in pots it doesn’t take long for them to lose turgor, past the permanent wilting stage. Once past this point, leaves fall, and only if the plants have enough strength and size can they recover to generate new growth. During the winter months warm, dry air from heating elements can devastate potted herbs quickly if there is a lapse in watering. In addition, many people do not water properly, watering plants too little at a time. The surface soil may look wet but water does not penetrate the soil enough to reach the deepest roots.

4. Overwatering. The flipside of the underwatering problem, is watering too much, another common problem. Most herbs cannot stand wet feet for long. The best defense against overwatering is to check your plants daily and when the soil feels dry water enough for water to come out of the bottom of the pots. If you water this way, you may not need to water again for a few days or as long as two weeks depending on local conditions, the type of plant and its growth stage.

As for the "white substance" on the undersides of the basil leaves, this is probably an opportunistic mould attacking a plant that is already weak. The common basils are really bested treated as annuals and as they get old (six months or older) growth begins to slow and plants eventually weaken to the point that they die from some opportunistic disease or pest. You may be able to prolong its life a month or two by spraying or dusting sulfur on the plant but that is unlikely to help much. We recommend starting new plants from seeds.

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