Indoor Herb Care – Winter Edition

Sarah's beautiful herbs, indoors and protected from the cold.

Sarah Mallin’s beautiful herbs, now indoors and protected from the cold.

After the past few frosty weeks, fresh herbs on the windowsill are a welcome sight in the home of a gardener with an itchy green thumb. Whether you’ve transplanted them from your garden or are eyeing some at the grocery store, we have a few tips for you to keep them in the best shape while they grow indoors throughout the next several months.

Type of pot and soil

Make sure your pot has a drainage hole at the bottom. If your decorative pot does not have a drainage hole, pot your herb plant in a plastic pot (with a drainage hole) that is slightly smaller than the decorative pot. Place this inside the decorative pot, and keep an eye on the water level so your plant roots aren’t sitting in water. If you’ve transplanted your herbs from outdoors, use lightweight potting soil to fill out the pot. A good potting soil will contain expanded perlite in addition to organic material. Perlite allows for better drainage and air flow around roots that are confined in a pot.

Light 

Right now in Chicagoland the days are not only growing shorter, but the sun is also positioned lower in the sky. This means that plants have much less light available, so you can expect them to grow more slowly. Be sure to put your plants in south or west facing windows where they can get at least six hours of light per day. If this isn’t an option, you might consider inexpensive grow lights to supplement. A 60-watt incandescent plant & aquarium bulb installed in a clip lamp 10″ inches above the plants will help during the darkest days of winter. If you are using a compact fluorescent bulb, you can position it just a few inches above the plants.

Rosemary gets hit with a sunbeam

Rosemary in a sunbeam

Fertilizer

With the plants growing more slowly, they also need less fertilizer. Be sure not to fertilize too heavily – a teaspoon of granular all-purpose fertilizer per foot of plant height is enough for 4-6 weeks indoors during winter. Mix the fertilizer in the planting hole before transplanting, or apply the fertilizer as a side dressing.

Water

Depending on the temperature of your home, you may need to water less or more frequently. Some Chicago-area homes have radiators near the windows, providing a very warm but also soil-drying environment. Likewise, homes with forced-air heat may be cooler near the windows and may retain soil moisture a bit longer. For potted plants, water when the top 1″ of the soil is dry, and be sure not to use softened water on plants. Softened water has essential plant minerals like calcium and magnesium removed, and sodium added. Too much sodium can build up in the potting soil and cause harm to plants, especially ones in a container environment.

Harvesting

Harvesting indoor herbs is much like harvesting herbs when they are growing outdoors. Keep in mind that since the plants are growing more slowly, it will take longer to recover from a harvest and produce new leaves. Aim for harvesting no more than 1/3 of the plant at a time, and harvest the outer or lower leaves first, leaving the central leaves which contain the growing tips alone.

The purple basil in the center of the picture has been harvested correctly. As the lower leaves are pinched off next to the stem, new ones will grow in place.

The purple basil in the center of the picture has been harvested correctly. As the lower leaves are pinched off next to the stem, new ones will grow in place. In the foreground, a basil cutting has sprouted roots in the glass and will soon be transplanted into potting soil.

For more information on growing and harvesting different herbs, check out The Garden Minute.

Buying herbs

Rosemary topiary

Rosemary topiary

Rosemary topiaries in the shape of holiday trees are popular during this time of year. Before buying rosemary, examine the leaf tips for browning or blackening. This indicates cold damage. While the plant may still be alive and new leaves can certainly grow in, the plant will be expending energy on repairing or growing new leaves at a time when sunlight is already scarce. It’s best to pick out one already in great condition. The rosemary should smell fresh and have green, springy leaves that do not break when touched. To transport home, make sure the plant is well wrapped in paper or burlap.

Basil leaves with cold-weather damage. In the background, typical leaf 'bronzing' seen with downy mildew.

Basil leaves with brown edges from cold-weather damage. In the background, typical leaf ‘bronzing’ seen with downy mildew.

Basil plants are also cold-sensitive. Above are basil leaves that are brown on the edges – a sign of cold weather damage. If you look in the background you can also see some signs of downy mildew. Although there are some treatments for downy mildew, it’s best to spend your money on an already-healthy plant. Again, make sure your plant is well wrapped in paper or burlap before transporting home. Even a few minutes exposed to the elements can damage the leaves.

Fresh herbs not only provide a pop of color to the windowsill, but also add color, nutrition and flavor to home-cooked meals. Some ideas:

Parsley – toss in a salad or add to chicken soup

Cilantro – add to salsa, rice or curry

Dill – use on potatoes or mix with sour cream/plain yogurt for a delicious vegetable dip

Thyme – toss with roasted vegetables

Sage – stir into squash risotto or Thanksgiving dressing

Basil – great in pasta sauce

Mint – make an herb simple syrup for flavoring tea

Tarragon – mix with softened butter and shallots for a delicious spread

Rosemary – add to macaroni and cheese or pound cake