Perhaps it is the lack of air circulation, too dry air, too
high temperatures and relatively low light levels; but herbs grown in the home
through the winter must be inspected frequently, so that any disease can be
controlled before it develops into a serious infestation.
I find that the main problems are with aphids which are
very commonly found on chervil, basil, marjoram and occasionally dill; white fly
which is particularly fond of the scented geraniums; spider mite which attacks
the lemon verbena as soon as it comes indoors (and there is never a sign of it
in the herb garden); and very occasionally the scale insect will try to become
established on sweet bay or myrtle.
The best protection against insects is to grow healthy
plants, because strong, sturdy plants seem to have an immunity; it is the weaker
ones that are attacked. To grow healthy plants indoors, it is very important to
see that they are potted in a lighter soil than they would have in the garden.
They need to have plenty of water, but must have good drainage at all times. The
mixture of three parts soil, one part peat moss and two parts sand is reliable,
but I would put at least one part compost in for every one part of soil. It is a
good idea to sterilize the soil if you are using it from the garden by heating
it to 200 degrees. (I put mine in an old roasting pan in the oven.) This will
ensure that you are not importing any insects from the garden.
Also, for the best health, herbs need a situation with good
air circulation, as much light as possible, and temperatures about 15 C. This
winter, I am moving all my herbs into an area in the basement where they will
grow under fluorescent lights. The temperature can be kept as much as ten
degrees less than the rest of the house, and as it is built of old limestone
walls, there is greater humidity than upstairs. I hope to have much healthier
plants.
Regular hygiene is the next important step. It is best to
inspect your herbs daily. If this is not practical, then make a point of
checking each one at least once a week. In this way, any insect infestation can
be dealt with before it becomes a problem. It is even better if at the same
time, you wash each plant in soapy water. If you cover the soil with aluminum
foil, you can dip small pots upside down in a bowl of soapy water, and rinse
them off with a gentle, tepid spray from the tap. Larger plants would have to be
sprayed with a soap solution, but they can be rinsed off by standing them in a
shower stall. The shower comes down like rain and the plants love it.
This treatment will prevent most insects from spreading,
but sometimes even the regular check misses a plant, and aphids and white fly
can spread at phenomenal speed, and before you know it, they are reproducing all
over the place. On these occasions, it is best to segregate the plants and take
more drastic action. As we eat herbs, I do not like to use any poisons on them
at all. In case of a severe infestation, I usually add garlic to the soap
solution, wash them more frequently, or in desperate cases, dispose of the
infected plants. However, some gardeners will use rotenone, others nicotene.
I hope that all your herbs will be so clean and well kept
that there will never be a need for a closer acquaintance with the insects which
we have mentioned. But in case there is, here are a few guidelines to help you
recognize what may be attacking your plants.
Aphids are small insects, either green, red, brown, or
black. I find the green ones are the most common. They weaken the plants by
sucking the sap, and if you see any of your plants looking sad, check the tips
of the branches for aphids. They seem to attack the weaker, or less healthy
plants, particularly ones which may have been kept too short of water. Regular
checking will guard against them, and washing with soapy water dislodges them.
White flies float up in a cloud when you disturb the
plants. Like aphids, they are sap suckers, but this time, it is the nymph or
non-adult form which does the damage. It has been shown that the white fly is
attracted to shiny yellow surfaces. Cards painted bright yellow, and covered
with "tanglefoot" or other sticky substances will lure the flies away from the
plants and catch them.
Spider mites are more difficult to see since they are so
small. But if the plants are dropping leaves, or turning brown at the edges,
turn the leaves over and look for minute little insects, which may be spinning
fine webs at the tips of the branches. Rinsing with a jet of water will dislodge
the mites, but the eggs are probably untouched, so to remove the whole
population, wash again in seven to ten days. By that time, the eggs will have
hatched, and the young mites will be cleaned off.
The scale insect is not often found on herbs, but it does
occur on the more woody plants such as sweet bay and myrtle. A bad infestation
will cover the plant with a shiny varnish, but the insect itself will appear as
small brown scabs. Unfortunately, the weekly wash, although it will protect the
plant, will not remove the insect, which must be scraped off with a fingernail
or a toothbrush. As well as insects, we do get some problems with fungus
diseases on plants grown indoors. Herbs, fortunately, are fairly free of these,
and the only one which is at all serious is mildew.
Mildew appears as a whitish
gray fuzz on the leaves and stems. It is almost always caused by poor air circulation in too damp surroundings. So, although we want a humid atmosphere, we
must see that there is a steady supply of fresh air. Young rosemary plants are
particularly prone to mildew if they are over-watered, or left in a place that
is too damp. I have also seen mildew on basil plants, too.I have not had any
problem with the fungus that causes "damping off" of small seedlings; perhaps
herbs are immune to this too. In fact, they can protect other plants. A tea made
from chamomile is said to prevent damping off if young seedlings are watered
with it.
Rachel McLeod founded Kiln Farm Herb Garden in Puslinch, Ontario in 1974.
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