U of I Master Gardener: What should be done in the garden before the first frost?

Now that the initial shock of “what I didn’t get done this summer” has worn off, it’s time to think about what can be accomplished before the snow flies.

According to the National Climate Data Center, Boise’s average first frost date is Sept. 22.

If you already have an herb garden, watch for the basil to die back. It’s the most frost tender of all herbs and is a signal that nights are getting cold and all other annuals will soon be gone.

If you have perennial herbs in pots that need to be brought inside for the winter, do so soon after the basil dies back.

If you don’t have an herb garden but have been thinking about starting one, first find a suitable space. Most herbs need full sun but will tolerate afternoon shade. That makes the east, northeast or southeast parts of the yard the best areas for an herb garden.

Some herbs are annual, some biannual and some are perennial. Some are grown for their leaves, some for their seeds. A Purdue University Advanced Master Gardener put together a list of herbs and the culture of each one. You can download the list and keep it for future use. Purdue University is in Zone 5, so any herbs that can be grown there can be grown in our Zone 6.

If you’re planning to grow mint in your herb garden, pay special attention to the instructions for this herb. It’s very invasive and should be grown in a container away from the garden. Cut off any flowers as soon as they appear or seeds will jump ship and take over your garden.

If you already have an herb garden, but need to know how to save seeds and leaves for future use, the University of Illinois has a list of herbs and how to harvest and preserve each one. Herbs listed as Tender Perennials need to be brought indoors for the winter or treated as an annual.

If the herb is grown for its leaves, don’t let it go to flower as flowering changes the flavor of the herb. When harvesting herbs throughout the growing season, cut no more than 1/3 of the leaves at any one time. Let the plant recover before cutting any more leaves.

One thing I’d like to do with my herb garden is to grow rosemary and train it into a topiary. I found a website with some photos and a good explanation of how to train rosemary and other herbs.

Not all varieties of rosemary can be trained into a topiary, though. Some upright cultivars that work well are Arp (hardy to Zone 6), Benenden Blue, Blue Boy, Golden Rain, Pine, Pink or Rex (all hardy in Zones 7-10).

If you have particular questions about gardening you’d like to see addressed in this column, send them to highprairielandscapedesign@yahoo.com.