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Search Results for: Hardy plants | Search the catalog for: Hardy plants

Plant Answer Line Question

Keywords: Hardy plants, Osmanthus

Is Osmanthus fragrans hardy enough to withstand winter in Bellevue, WA?


Osmanthus fragrans is a borderline hardy shrub in our area. References vary in the hardiness they quote from zone 7 to zone 9 (Bellevue is zone 8). According to a gardener here at the Center for Urban Horticulture, "it takes a special spot for it to grow and thrive here in the Puget Sound area. The places where I've seen decent specimens and blooms are plants growing up against a warm wall or enclosed somehow by other plantings, buildings, or areas near pavement." If you have a very sheltered spot, for example a courtyard where you could grow it against a south-facing wall, it might be worth a try. Otherwise it seems to be very risky.

Date 2017-05-17
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Plant Answer Line Question

Keywords: Frost, Hardy plants, Rhododendron

A friend in Illinois has sent a photo this spring of a very healthy looking rhododendron - leaf buds fully elongated and beginning to unfurl, while the green, blunt flower buds remain unopened. The flower buds don't look brown, diseased, frozen or injured, but they remain tightly closed, foliage bud growth preceding blooming. He says he has 6 plants doing the same this month. Possible reason?


Though we can't diagnose plant problems by phone/email, early autumn frosts can inhibit flowering and not all buds are equally affected.

"Autumn frosts: These can lead to damage...if they either occur in early autumn or immediately after a late season warm spell. Continental climates with extremes of heat and cold are more likely to suffer sudden temperature changes than those with maritime climates...A sudden temperature drop will catch a plant before it has had a chance to reach maximum hardiness and it may suffer accordingly, even if normally perfectly able to withstand such a temperature in mid-winter...Speed of ripening varies considerably...There is also a variation in the hardiness of flower buds compared to foliage and growth buds. Commonly, flower buds may be as much as 10 F. less hardy than foliage..."
(Source: The Cultivation of Rhododendrons, by P. Cox, 1993, p. 119-120)

Date 2017-08-15
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Plant Answer Line Question

Keywords: Hardy plants, Alstroemeria

Is there a list of the more cold hardy Alstroemerias?


Here is some general information on Alstroemeria from North Carolina State University Extension, which indicates they are generally hardy to 23 degrees.

The Royal Horticultural Society's A-Z Encyclopedia of Garden Plants, edited by Christopher Brickell (DK PUblishing, 1996) says Alstroemeria aurea and A. ligtu and their hybrids are able to tolerate brief drops in temperature to 5 degrees Fahrenheit.

Date 2017-12-08
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Plant Answer Line Question

Keywords: Hardy plants

When a plant is assigned a zone or temperature tolerance, is it the actual temperature of the air or is wind chill temperature counted? In other words, if I have a plant that tolerates temps to 20 degrees and the temp today is 28, but the wind chill is 15, is my plant still hardy?


Here is a link to the frost zone map for the U.S.

Apparently, wind chill does not affect deciduous plants. If your evergreen plants are sheltered from the effects of the wind, then they may be protected from moisture loss. Below is additional information about plants and wind chill.

From Portland, OR area garden writer Ketzel Levine:

"Wind chill has little effect on deciduous plants, so if we're talking forsythia and blueberry, it's not an issue. Of course it does becomes an issue if the subject is broadleaf evergreens (boxwood, hollies, osmanthus, etc.) and to a lesser degree, needled evergreens. Sub-freezing winds rob leaves of moisture, a serious problem if a plant continues to photosynthesize through winter. But the USDA zones do not take wind chill into consideration, and if I were you, I wouldn't either. If you're not a risk taker, stick with Z6 plants; otherwise, let the cold winds blow."

From Rob Gough, Montana State University Extension agent:

"Do plants feel wind chill like we do? It sure feels a lot colder to us when the wind is blowing. It makes 30° feel like 0°. Meteorologists express this feeling by the term 'wind chill' and we often hear wind chill advisories on the local radio station. Do plants feel wind chill? Does a wind chill of 25° below make the plant react as though it were that cold?

The answer is in the word 'feel.' The term 'wind chill' was developed to express how the combination of wind speed and temperature 'feel' on exposed skin. The skin has nerves which transmit that feeling to the brain and we say, 'Boy, it sure feels a lot colder than 30 degrees with all this wind.' But the plant doesn't feel. It has no nerves to transmit that impulse. So to use the term 'wind chill' in relation to plants is meaningless. But that's not to say that wind and cold do not affect plants. Last time I told you how cold influences plants. Wind plays an important role too. Wind can increase the evaporation of soil moisture, thus speeding drying and making water harder for the plant to come by. Wind also speeds evaporation of moisture from the plant surface. Even without leaves, deciduous plants can lose moisture through their young bark. The faster the wind, the faster moisture is lost.

You may notice the windward side of your evergreens are scorched, or burned. The needles are brown or reddish on that side. That's windburn and it's simply desiccation of tissue caused by the wind. Again, like cold damage, wind damage is also the result of drying out of the tissues. If you want to know more about winter damage, contact your county extension office."

Date 2018-03-15
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May 23 2018 14:32:42