More About Herbs in a Windowsill Box
Answered by: Conrad Richter
Question from: Yuan Yu
Posted on: June 29, 2003

I ordered some Bay, Baby PJ Rosemary, Creeping Savory, Winter Savory, and several Thyme varieties. I plan to group a Bay tree (when it is still small), a Baby PJ rosemary, a Creeping Savory, and three Thyme varieties into one 6"x6"x24" windowsill box. You recommended to plant herbs in their own pots then in the window box. However I have difficulties to find right size of pots that fits into the window box. I am thinking whether I can use transparency film (the plastic sheet used for projectors) or some other similar plastic sheet to make a 6" diameter cylinders and cut them to be 5"H. Then use the film made cylinder as pots in the window box. Do you think this alternative planting system will serve the same purpose of the planter box system that you recommended in "Popular Herbs Grow Happily Indoors"? Is there any chemical in transparency film that may not be proper to be buried into soil with herbs?

I am not sure if there are any chemicals in transparency film that would be a problem for herbs. If you don’t have access to plastic pots, you can use 1 liter yogurt containers. If they are too tall for your windowbox, just cut them down. But make sure you put at least 6 holes in the bottom for drainage.

Do thymes die back or go dormat in winter? How about sages, oregano, mint, and chives?

In the garden, they do – of course. Indoors they can also go dormant or can enter a slow growth phase in the winter when the days are short and the sunlight intensity is lowest. If however the winter temperature is warm (room temperature) and the plants are getting supplementary artificial light as well as the natural daytime sunlight, there is no reason why most herbs can’t continue to grow as in the summer months. Chives and tarragon are two herbs that seem to like a winter break from growing, even if the light is strong.

I have another question about how to overwinter potted herbs outdoors. I have several varieties of sages, thymes, oreganos, rosemary, chives, and mints. Most of them are grown in 12" pots. Some in 10" pots, or 6"x6"x24" window boxes. I can only bring a few of them indoors in winter. I am living in Zone 6. I originally planned to leave those winter hardy more or equal to Zone 6 outdoors in winter. I just realize that when planted in containers plants will be hardy to two zones less than in the soil. Will those potted herbs that only hardy to Zone 5 or 6 die from cold in winter? I may be able to buy one or two mini-green houses (3-4 tier plant shelf with a removable UV coated plastic cover), and place the only hardy to Zone 5, 6 herbs inside the mini-green house in the winter. Do you think this method will make sure those plants get through the winter here?

The rosemary won’t survive outdoors in pots outdoors. If the greenhouses will be heated then put the rosemary there. Other than the common garden sage and related varieties (such as Berggarten sage), most sages will have to overwintered in the heated greenhouse also. Most thymes, chives, oreganos (but not Kalitera and Cretan) and mints will survive in those pots if you "heel in" the pots. "Heeling in" means to dig the pots in the soil so that the rim of the pots meets the ground surface level. In spring you can simply lift the pots and move them to their growing positions. A winter mulch of straw or dead leaves is advisable; apply after the ground is frozen but before the first permanent snow fall.

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