Indoor herb gardens seem so easy to maintain, yet they can so easily fall short. To grow your own herbs at home year-round, graduate from the odd assortment of pots on the kitchen windowsill–where herb plants are sentenced to die in so many households–and follow these herbal do’s and don’ts.
Growing fresh herbs indoors saves you money, makes the food you cook taste better, and reminds you why it’s good to be alive. Seriously. If you’re feeling down, harried or uninspired, go to your personal herb garden and breathe it in, slow and deep. Instant aromatherapy.
Nothing against kitchen windowsills in general — that’s certainly a handy place to grow herbs and sometimes it works fine. But you need to understand the conditions each plant requires. Some herbs that work great together in, say, a pot of stew, don’t thrive when planted side by side.
Here are some ideas about what to do and what not to do for your next herb garden:
DO: Start with Seeds
The last thing you want to bring into your home is an herb plant that introduces pests and diseases to other herbs and other indoor plants. It’s easy to miss the single visible aphid on an otherwise gorgeous looking plant. But if there’s one, there are probably many, many more.
Growing herbs from seeds in an indoor greenhouse with a controlled environment is ideal for preventing the spread of disease and unwanted bugs.
One reason is that you can control the humidity. Hot, dry air pumped through your home by a furnace or air conditioner can stress your herbs, making them more susceptible to spider mites, aphids, etc.
Another advantage of seeds is that you can get them anytime of year. Plant cuttings can be effective, but it’s often best to take cuttings from herbs growing outdoors. Different herbs require different handling of cuttings. Seeds are simpler and safer — just follow directions on the packet.
DON’T: Group Herbs That Don’t Grow Well Together
Blame Simon and Garfunkel. The well-known refrain of their song, Scarborough Fair, cemented the combination of parsley, sage, rosemary and thyme in the minds of a generation (or two) of future herb growing enthusiasts.
Growing these four herbs in the same container, however, doesn’t always work well. Although all these plants like plenty of sunlight, parsley generally grows well in moist soil and the other three do better in drier, more sandy soil.
Here’s a breakdown of common varieties of herbs that prefer relatively wet vs. dry soil:
- Wet – basil, chives, chervil, cilantro/coriander, mint, parsley, tarragon
- Dry – bay, lavender, marjoram, oregano, rosemary, sage, thyme
In addition to differing amounts of water (see below), you may want to use different soil for these two groups. In both cases, avoid using dirt from your yard or garden — it’s too likely to contain damaging micro-organisms and pests. Use a clean potting soil mix.
For the herbs that prefer drier conditions: Blend two parts potting soil with one part sand or perlite, and be sure the container has good drainage. Some indoor gardeners add a bit of lime juice to the soil to recreate the more alkaline Mediterranean soil most varieties of these herbs prefer.
It might be best not to include plants from the mint family in the same container as other herbs. Mint spreads laterally very quickly, sending out runners than can overwhelm its container mates. Why is mint so anti-social? The answer lies at the bottom of your next mojito, my friend.
DO: Use Grow Lights
Most herb varieties need more sunlight than other house plants to really thrive. Herbs that don’t get enough light won’t produce as much of the essential oils that give these plants their distinctive aroma and flavor.
If you’ve got a south-facing window that gets at least four hours of direct sunlight per day, most herbs can stay alive there, but may not achieve the potency you want for cooking or herbal tea. Use a good grow light, such as a T5 full-spectrum bulb, to light herbs up to 18 hours per day.
Much of the work of maintaining herbs indoors comes from the need to move them from room to room and rotate the containers to chase the available sunlight. Again, an indoor greenhouse with programmable light cycles solves this problem nicely, yielding abundant, highly aromatic herbs.
If you use grow lights, try to give your herbs at least six hours of complete darkness, which is important for them to complete the heavy lifting of photosynthesis: converting energy into food.
Waterlogged roots (or “wet feet”) are one of the main reasons herbs fail in an indoor garden. Even the varieties described above as liking “wet” conditions won’t live long if water doesn’t drain beyond their roots.
A general rule is to water herbs until you see a bit of moisture drain out the bottom of the container. How often to water depends on the humidity where the plants are. Stick your finger in the soil often — a few times a week at least — to see if the soil is moist.
Help your herb roots stay healthy by using unglazed terra cotta containers rather than plastic containers if you can. Moisture and air can escape through terra cotta, but not through plastic.
Even the plants listed above as liking dry conditions shouldn’t have completely dry soil–just a little drier than those in the “wet” category.
One reason kitchen window sills aren’t always the best place for herbs is that the air is too humid, especially if the window is above the sink. It makes sense to have your herbs near where you cook, but some herbs (especially rosemary) may not survive a kitchen’s extra humidity for long.
DO: Prune Early and Often
In general, the earlier you start pruning your herb plants, the more you’ll eventually be able to harvest. Your goal is for the plant to be wide and thick, rather than skinny and tall. So, start at the tallest stem, and cut just above a leaf “joint,” where new leaves sprout from the stem.
Pruning the tallest plants first is important, because then you can get your grow lights down closer to the tops of your plants. Try to get the lights about four inches from the tops of your shortest plants.
Avoid these three common mistakes when pruning/harvesting your herbs:
- Cutting or pinching just below a leaf joint, leaving a section of empty stem at the top. This will cause your plant to grow too tall and leggy.
- Removing the largest leaves near the bottom of a plant. These big leaves are like the the giant panels used in solar energy arrays — leave them intact as long as they’re healthy.
- Cutting too much of the herb at once. Try never to cut more than about one third of an herb plant at once.
Look at this simple drawing from the Growing Stories blog of where to cut when pruning herb plants. (Note: This illustration uses the term “armpits” to describe the underside of a leaf joint. We don’t call it that because putting armpits in your marinara sounds…icky.)
Try to prune stems before they flower and go to seed (unless the herb has edible flowers you need). Pinch off flower buds if you see them forming. If the stem continues to try to flower, just cut that stem off if necessary.
When you first being growing herbs, consider trying just two or three of your favorites and see how it goes. Warning: You may quickly become an herb snob, turning up your nose at the $3 to $5 packets of herbs at the grocery store.
Even better, you can experiment with a huge variety of herbs you won’t see for sale at most stores. And with fresh herbs always at your fingertips, at the very least you will have nice smelling fingertips.