Gardening tasks change as Idaho weather heads into fall

As we approach the end of this growing season, we should continue to plan ahead for our plants in the ground and those we’re saving for next year. Continue to water as necessary and weed wherever possible. Some plants such as geraniums may be moved to your garage or crawl space, to lie or hang dormant until spring. Their roots will need an occasional spritz of water. Or take cuttings and start plants anew. Some folks uproot them and hang plants upside down; others just leave them in their pots. Still other folks take cuttings and stick those in unfertilized potting soil.

For those plants looking forward to dormancy for a time (such as lemon verbena, for instance), do not repot, especially with a potting mix containing fertilizer. The plant wants to sleep, not grow. I’ll bring potted herbs such as oregano, rosemary, tarragon, za-atar, lemon grass, thyme, lemon winter savory, and some chile plants into the greenhouse for winter. Some of my fish chile plants are beautifully variegated this year, and I’d like to keep those plants going. That’s a very old variety preserved by folks of recent African ancestry who used those hot chiles in fish and turtle soups, especially in the Maryland-Delaware-Pennsylvania areas.

Herbs such as sage, chives, oregano and thyme can survive even our cold winters outdoors, but I bring some into the greenhouse for convenient use during wintry days. My summer savory reseeded itself last year in a container, providing a super easy crop of that great bean herb for me to dehydrate over summer. Now it’s going to seed again, so I’ll just let it reseed again in that container. I’m moving Thai, Tulsi, Mexican and Persian basils into the greenhouse until they give up the “annual” ghost. I’ve made a lot of pesto from sweet basil that’s now in the freezer.

For those readers new to this valley, our average date of killing frost is around Oct. 9 or 10. In the past, we’ve usually had a night or two of frost, then a week or more of “Indian summer,” prolonging a glorious autumn. Thus it would help for you to have old sheets, blankets or mattress pads ready to cover frost-tender but still-bearing plants such as tomatoes, sweet potatoes, beans, peppers and eggplants. Uncover them days, cover again on frost-predicted nights. The coldest temperatures occur just after dawn, so if you’re an early riser, you may be able to protect your plants in early morning by turning on sprinklers or a fan instead of covering. By that time we’ve usually had our sprinkler system blown out, so don’t have availability of sprinkler to prevent frost.

Don’t try to overwinter root crops in the soil. My experience has been that they crack open, letting burrowing critters have their way. Pull or dig carrots. turnips and potatoes. Parsnips, like kale and collards, get sweeter after being frosted.

One of the reasons I dislike growing pole beans is that they set pods so late. Mine have set in late August and early September. In the past, we’ve torn down those plants and set green pods to dry on hardware cloth in the greenhouse, but some of those have molded. Moldy beans may be toxic, so I only use those as seed for subsequent crops. They do outgrow the mold-toxin effect. This spring I noticed we had overlooked a pole bean pod on a trellis, and left it through the harsh winter. I opened the pod, and the dry beans appeared to be perfect.

This is not a topic most garden references take on, so I asked friends online who garden in colder climates than ours. A fellow in Michigan said he had left them out over winter, and they were fine. He did say, though, that he had harvested some and dried them on his porch, where they grew moldy.

What about roses?

In the past, many rose fanciers in the Treasure Valley have done little or nothing to protect their roses over winter, but may be changing that habit after last winter’s rose-killing cold. Sandie Ford has about a hundred rose bushes, and she lost none last year. Some canes were bad, but the bushes themselves survived last winter.

She said she piles leaves from her maple tree over the crowns of the bushes, to a depth of 3 or 4 inches, and adds compost on top to hold the leaves from blowing away. I’m sure that lingering snowpack assisted in holding the leaves in place. Since she has so many rose bushes, it’s not really feasible to use commercial rose cones for winterizing, but they are available at local garden centers for those who would rather not buy new shrubs in spring and don’t have access to enough leaves.

Don’t cut rose canes back in autumn unless they’re long and liable to whip in wind, injuring other canes. Ford said in spring, when she raked leaves aside, she cut canes back to about 3 or 4 inches in height, removing those that had winterkilled, and the rest then sprang to life.

This story was originally published September 20, 2017 at 3:54 PM with the headline "Gardening tasks change as Idaho weather heads into fall."