University of Vermont Extension 
Department of Plant and Soil Science

 Winter News Article

Dr. Leonard Perry, Extension Professor
University of Vermont
An indoor kitchen herb garden will add flavor  to your meals and color to your window sills...and help satisfy that gardening desire during the cold, wintry months.

Most culinary herbs require at least five hours of sun per day. You can use a sunny window, provided the reflected heat is not too intense. If you don't have a window with direct sunlight, put your pots of herbs in a spot with plenty of light, then move them into the sun for a few hours whenever possible.  Winter is a good time to start herbs as the sun is getting brighter and the days longer as the plants grow.

Fluorescent lights, or special grow lamps, also work if left on about 14 to 16 hours per day. Place the lights 6 to 12 inches above the tops of the plants, if possible. If the light source is too far away, insufficient light will reach the plants, and they won't grow.  If using fluorescent lights, alternate warm and cool white bulbs in the tube fixture, or use ones listed for “natural” light.  If you just have a pot of herbs or two, you can use a spot lamp near them. 

You must also consider temperature and humidity. Most herbs need daytime temperatures of 68 to 70 degrees F with 30 to 50 percent humidity. To increase humidity, place a dish of water near the plants, or place the pots on a tray of pebbles you keep moist.

Pot your herbs in a mix of vermiculite or equal parts peat moss, garden loam, and coarse sand. Or buy a potting mix with such ingredients, but not the heavy garden loam.  The potting mix should be slightly moist before sowing. Any container will do, as long as it has good drainage.  You may want to start seedlings in a small flat or pot, then transplant as they grow.  Sow the seeds according to the package directions, but no deeper than two times the diameter of the seed.

After planting, lightly water with the spray nozzle on a sink, or mister.   Place each container inside a plastic bag to create a "greenhouse," leaving the top slightly open to allow some air and moisture to escape. Set in a fairly warm location (65 to 75 degrees F) out of direct sunlight until seeds germinate.  Don’t place on a wood stove or too near, as the soil may stay too warm.  If near forced air heat vents, check often as this can dry out the soil and seeds.

Germination should start in two to three weeks. At that time, remove the plastic, and move the container to a cooler area (60 to 70 degrees F) where it will receive good light but not direct sun, unless for only a few hours in the day. Gradually increase the amount of sunlight if possible, and rotate pots for even exposure to sunlight. Continue to water, but don't overdo it or the plants may rot. 

Thin your herbs when the seedlings have two sets of true leaves. If you started herbs in flats, this is the time to transplant them to individual pots. Use a similar potting medium as used for germination, or as for potting houseplants.
Herbs generally need little fertilizer, but will respond to some. Use a soluble liquid or dry fertilizer, and apply at half strength based on label directions. Liquid seaweed works well on many.  Over-fertilized plants often have a poorer flavor than those grown at a more moderate rate.

Potential problems growing herbs indoors are pests that you don’t see outdoors, due to natural predators there and the rain washing them off.  You can simulate the latter by regular gentle showers or baths for your mature plants.  If you wash them in soapy water, make sure it is quite dilute, otherwise the soap may injure the leaves.  If using organic sprays such as insecticidal soaps, make sure to read the label and check if herbs and edible plants are listed.  Watch, in particular, for aphids and spider mites.

Some easy-to-grow annual herbs that can be transplanted to your garden next spring include basil, parsley, dill, oregano, chives, coriander, tarragon, and anise.  I like to have a pot of mint handy for adding to peas (English style serving), or hot tea.  Mint, of course, is a vigorously spreading garden perennial that you may want to keep in a pot next summer. 

Some herbs are more commonly started from cuttings, so if you didn’t do so last season, you may want to look for these are garden stores or in catalogs.  Bay is a woody plant that does well in containers year round, and of course its leaves are common in Italian sauces as is thyme—another one to look for as a plant.  Rosemary is another woody plant, growing as a shrub in hot and Mediterranean climates.  Yet I find it will tolerate cool, but non-freezing, conditions. 

If planting your herbs outdoors this spring after frost, or starting an herb garden this summer, mark your calendar now to dig some plants next fall to bring indoors before frost for next year’s indoor herb garden.

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