Bringing Herbs Indoors for the Winter

It's almost time to say goodbye to your outdoor herb garden for the season. If you planted your herbs last spring thinking fall would be a welcome relief from weeding, pruning and insect control, you might be surprised at how sad it can feel to abandon your pampered annuals and perennials for the cozy comforts of the indoors. There may be another option -- for some of your herbs, anyway. Bring them indoors with you.

Wintering Herbs Indoors

Before you grab a trowel and some pots, there are a few things to consider.

If you live in an area that experiences harsh winter weather, your perpetual outdoor herb garden will be restricted to winter hardy varieties like the mints (mint, catnip, lemon balm), some sage varieties, oregano and others. Plants like aloe vera, rosemary, pineapple sage and lemon eucalyptus won't overwinter outdoors, but they may survive inside.

Before you think about relocating or propagating herbs for an indoor garden, though:

Read up on the herb varieties you have, and know your growing zone. There's a handy herb listing at the left of this article that should help. If the herbs in your garden are hardy for your area and are nicely planted in the ground, your best option is to leave them where they are. Just give them a nice pruning and put down a layer of protective mulch. If you like the idea of keeping some winter herbs on your windowsill, consider taking cuttings to start in water. This won't work for all types of herbs. (Read on for more information.)

If you have herbs in pots on your deck or patio, freezing temps will kill their roots. To get them through the winter, you have a few options:

• Bury the pots in the ground and dig them up again in spring. This will work for winter hearty herb varieties.
• Replant the herbs in the ground. It's getting late in the year for this, but it may still be doable.
• Bring the pots indoors. This can work for most herb varieties if you have a sunny window in which to stow them. By sunny I mean around six hours of light a day (bright enough to cast a shadow). You can supplement with grow lights if you have to.

If you do bring plants indoors:

• Prune them first by removing a half to two thirds of the top growth (this varies from variety to variety, remove less for slow growers).
• Spray plants with insecticidal soap before you relocate them and check again for insect activity on moving day.
• If your herbs are big drinkers, give their pots a nice layer of mulch to keep the indoor watering schedule reasonable. (This works for plants that like higher humidity, too.)
• Isolate the refugees from your houseplants for the first couple of weeks to make sure no destructive insect freeloaders have survived to wreak havoc on your indoor garden.
• Although there are exceptions, most overwintering plants will be dormant or conserving energy during the winter months and will not require much if any fertilizer.
• Keep plants away from heat sources (like heat registers) and drafts (from windows and exterior doors).

Starting New Herb Plants in Water

If you have outdoor plants you'd like to propagate for spring planting, you may be able to get a jump on that now by starting stem cuttings in water. This can be a fun and inexpensive way to grow new plants. You can typically start stem cuttings any time during the growing season -- although I will admit that spring is usually a better time than fall. The fact is, though, that starting baby plants over the winter can be a fun project, and there's not that much of a down side. If it works, it works.
Here are some tips:

• Take six inch long stem cuttings.
• Use a very sharp knife to make the cuts.
• Cut plants at the juncture just below where new leaves emerge (leaf nodes).
• Strip the leaves on the lower two thirds of the stem.
• Take half again as many cuttings as you think you'll need. Some won't root.
• Place the stems in water. No leaves should extend below the water line. The container isn't too important as long as it's clean.
• Replace the water every three days or so with fresh. After about a month, you can cut back to once a week.
• Turn the container so all sides have equal access to the available light. (I try to turn containers every couple of days.)
• It may take up to six weeks for some cuttings to root, so be patient.
• Discard decaying stems promptly and replace the water.
• When cuttings have established roots of a half-inch to an inch-long, pot them. You can use starter pots and peat potting mix. For the mints and other moisture hungry herbs, as an interim step I like to repot into large freezer bags with three inches of potting soil on the bottom (around three seedlings per bag). When the weather starts to warm up, I transplant to large peat pots -- the last step before putting these new plants outdoors after the last frost in spring.
• Choose perennial plants. These varieties are relatively easy to root in water: basil, pineapple sage, catnip, rosemary, oregano, lavender and mint (mostly). I have trouble with mint from time to time. Not all herb varieties will root in water.  If you want to try rooting an herb that isn't listed here, it never hurts to give it a try. You may want to hedge you bets by starting a few stems in sand, vermiculite or a soilless potting mixture (dust the stripped, soil bound ends with rooting compound first - you can find it at your local nursery). 

If you enjoy your outdoor herb garden, you'll probably like starting new plants this way or bringing some of your outdoor favorites inside. Come spring, there are few garden tasks nicer than reintroducing your winter expatriates back into the garden.

Special hint: If you do transplant rooted stems to plastic bags, leave the bags slightly open and breath into them every few days -- plants like the CO2 (this works well in a terrarium or conservatory, too).