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Leafless Green Ash in Late May 2013

“What’s the deal with the trees this spring?!”

After the spring of 2012’s phenomenally warm temperatures and early leaves and blooms, you, like many, have probably been wondering about some of the still-leafless trees this late spring. Yes, the overly chilly temperatures have slowed some leafing down a bit, but there is more to the story than that.

You may have noticed some of our earliest leafing (and flowering) trees starting to do their thing in early-to-mid April. Then…duhn, duhn, DUH! We had (at least) three late hard freezes about a week apart in April.

When a hard freeze hits early during a deciduous tree’s leafing out stage, those first leaves are killed by the freeze. It then has to put a tremendous amount of energy into generating a second set of leaves for that year. Hence, the tree will appear to leaf out much later than usual. In my garden, this happened with the amur maples this year. Often this second set of leaves may be slightly smaller than usual. It stresses the tree to have to do this, though they usually can recover without much help from us. The one thing homeowners can do is to eliminate the use of any weed killers to lawn areas above the root system of these trees this year as they will be more sensitive to pesticide applications.

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Leafless Kentucky Coffeetree in Late May 2013

With early flowering trees, the flower buds can be frozen and killed by hard freezes, and the tree usually doesn’t generate a new round of flower buds. That year’s bloom is just entirely lost. This was sadly illustrated by the lack of crabapple blooms this past April.

Other trees were probably just entering the leafing out stage when the freezes hit, and they threw on the brakes until after the cold weather. They didn’t lose those first leaves, they just put them out a little bit later. And then the trees that would normally leaf out later just pressed on with their regular schedule. This has led to a somewhat strange leafing out order for our trees this year, with many of the later-leafing trees actually leafing out first this year. Then they were followed by those that put off leafing and then by those that had to generate a second set of leaves. At this point, the ash and elm trees (traditionally earlier leafers) are just now putting out tiny leaves. Other trees look like they are still completely bare, but if you were able to get a good close look at their branches, you would probably see very small leaf buds starting to swell.

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Green Ash Putting Out a Second Leaf Set in Late May 2013

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Ohio Buckeye Leafed Out and Flowering Normally in Late May 2013

So take heart, our trees really are going to all leaf out, it’s just taking some of them much longer than usual.
Contributed by Carey Harrington, Certified Colorado Gardener and Colorado Native Plant Master

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