Flowers have critical temperature requirements, too

Last week I discussed temperature requirements for different vegetable crops. Flowers are not all the same either.

Some hardy annuals like pansies are usually planted in the fall around here. They tolerate cold soils and temperatures below freezing. Snapdragons aren’t as cold hardy as pansies, but they’re close. Both tend to melt out in summer in eastern North Carolina.

Calendula and dusty miller withstand significant frost. Dusty miller are biennials. They live through winter and bloom the following spring. Torenia is another one that can be planted early in cold soils.

Geranium and petunia resist some frost if they are well established. Their growth is slowed dramatically by cold soils though. In fall when soils are warmer they continue to grow after several freezes.

Some flowers simply need warmer temperatures and pushing the limit is seldom successful. Marigolds and zinnias don’t adapt well to cool soils or strong spring winds. They’re heat lovers. Many full sun plants are like that.

Flowers need not be sun-loving to be cold sensitive though. Wax begonia and impatiens prefer shady conditions. They even grow prolifically in cool temperatures, but they don’t handle frost well at all.

Celosia, ageratum, salvia, cosmos and vinca are fine planted in pots early in the season. Avoid putting them in the ground until things have warmed up a little.

Portulaca likes things hot and sunny. It should never be planted in cold soil. It holds well into fall when soils are warm, but wet soils in spring are a problem. Phosphorus fertilization is also important as plants don’t extract phosphorus efficiently on cold soils.

In spring, wet soils mean cold soils. Plants need to be watered, but it’s dancing a fine line when gardeners try to push the spring. In summer it can be hard to keep some plants wet enough. When soil temperatures are in the 40s, like most are now, routine watering without checking first can mean root rot among other things.

One consideration for planting bedding plants is whether we’re talking about seeding or setting plants. If we sow seed, soil temperatures are more important than air temperatures. Air temperatures are more critical when setting out seedlings.

In this area another important consideration is wind. The Wright Brothers didn’t come to this region for nothing. Wind can dry plants out. It also can whip tender seedlings around, breaking them off and shredding their leaves.

For this reason, hardening plants off before planting is critical. Generally, bedding plants should not go directly from the greenhouse to the field this early in the season.

I like to find a protected spot where plants can be in a milder environment than their final planting spot. It must be out of the wind. During the hardening off period plants should receive less water than they otherwise would in the greenhouse.

By this I mean they should be slightly water stressed. This will promote a stronger root system and that will make a difference when they are transferred to the bed.

The greatest asset a gardener can have is patience. A few days of patience in the spring will continue to pay dividends all the way to fall.


Ted Manzer teaches agriculture at Northeastern High School (

About tedmanzer

I grew up in Old Town Maine and got a B.S. at the University of Maine in Plant Sciences/ minor in Botany. From there I moved to West Virginia and earned a M.S. in Agronomy at WVU. I also met my wife there. She grew up in rural WV as the daughter of tenant farmers who raised cattle and hogs. Their lifestyle at times was one of subsistence and I learned a lot from them. I've always been a foraging buff, but combining my formal botanical knowledge with their practical 'Foxfire-type' background opened up my eyes a little more. I recently retired from teaching high school agriculture after 25 years teaching with my wife. Until recently I wrote a weekly nature/foraging column for the local paper ( I also have written several Christian nature/adventure novels that can be purchased on Amazon in Kindle format. One is a five book family saga I call the 'Forgotten Virtues' series. In the first book, Never Alone (presently out of print), a young boy comes of age after his father dies in a plane crash, and he has to make it alone. The second book, Strange Courage, takes Carl from his High School graduation to his recovery from a nasty divorce. The third book, Second Chances, takes Carl from his ex-wife's death and the custody of his son to his heroic death at age 59. The fourth book, Promises Kept, depicts how his grandchildren react and adjust to his death (this one is not yet published). In the final book, Grandfather's Way, his youngest and most timid granddaughter emerges from the shadow of her overachieving family and accomplishes more in four months than most do in a lifetime. I use many foraging references with a lot of the plants I profile in these articles in those books. I also wrote a romance novel titled Virginia. It is available on Amazon and is a different type of romance from a man's perspective.
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1 Response to Flowers have critical temperature requirements, too

  1. tonytomeo says:

    This is why the coo season annuals get replaced with warm season annuals.

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