Lauterbach: Adjust growing time for day length

Special to the Idaho StatesmanJuly 19, 2013 

Sweet potato plants tend to thrive in the shorter fall days.


If you're planting for a fall crop, allow for more days to maturity than what the seed packet says because plants grow more slowly during the cooler fall weather than when they are planted during the lengthening, bright days of spring. And be aware of that longer growing period bumping into the first killing frost.

Worse yet, days are growing shorter, and some plants are sensitive to length of daylight hours. This "day length," best known to gardeners with regard to onions and strawberries, actually refers to the length of night. It's the length of night that controls plant growth.

This is known as "photoperiodism," and in plants, their optimum day length is the stimulus for flowering.

Long-day plants grow best in spring, when days are growing longer and longer. Those include lettuce, onions, potatoes, spinach, carrots, beets, lentils, turnips and artichokes, for instance. Peas are also a long-day crop.

That means it's hard to get peas to blossom and set pods late in the fall, when days are definitely shorter. If you want to grow peas for a fall crop, time your sowing so they'll produce a harvestable crop by the autumnal equinox, or very close to that date. This year it will be Sept. 22. After that date, daylight hours diminish.

Ornamental plants, too, respond to length of daylight (night hours). Chrysanthemums and poinsettias, for instance, are short-day plants. Asters are special, requiring long days then short days before they bloom their best. Easter lilies' normal blossoming takes place during long days, so to get them to bloom by Easter, they have to be exposed to supplemental light.

Few of us grow the food crops that grow best in short daylight hours. Those include black-eyed peas, Mung beans, rice and soybeans. Another that grows best in short daylight hours is the sweet potato. Perhaps that's why some sources say sweet potatoes double their yield every two weeks in the month of September. Their yield increases more slowly after that until their vines are destroyed by frost.

In my garden, sweet potatoes usually have one end sticking above the soil line, and those protruding tubers would be vulnerable to frost too, so we harvest before the first frost.

Vegetables such as Brussels sprouts, cabbage and kale are day neutral, but they're flavor-enhanced by frost, while tomatoes, corn and cucumbers, also day neutral, are destroyed by frost.


The battle against squash bugs is on in our Valley. I had read that Nasturtiums repelled them, so I planted Nasturtiums between each of my squash plants.

The seedlings were small, and were quickly overshadowed by vigorous squash plants. Only one plant kept up with the squash's rapid growth. That plant doesn't seem to have as many eggs laid on its leaves as the other plants, so I think next year I'll start with larger Nasturtium plants when I direct seed squash.

I am patrolling daily for squash bug eggs, spraying them with Neem. I was beginning to think squash bugs were trying to outsmart me, laying eggs on top of leaves, on leaf stems and in much smaller clusters until I heard from a friend who lives near Star, complaining her squash bugs were doing the same thing.

She had just been scraping off the eggs instead of spraying them with Neem and leaving them in place. I had killed a couple of dozen adult squash bugs, when a friend in the North End said she had killed two. There are few areas in the North End that receive sufficient sunlight for squash to grow, but only two squash bugs? Perhaps they target more open areas, free of large trees.

Send garden questions to or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

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