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How to Handle a ‘Diseased Dogwood’

Q. I have a dogwood tree in my yard I’m really concerned about. It was planted about three years ago in what I now realize is a very hot afternoon sun location (probably not ideal). Its leaves look brown every year and it has not yet flowered. I thought it was drought stressed, so this season I really kept on top of watering it with a soaker hose. It started leafing out, but by early summer the leaves began to look dry and about 50% of each leaf curled inward. An arborist I called said the tree suffers from anthracnose and will need an annual fungicide spray; non-organic. I am hoping there are other options.
    ---Jennifer in South Jersey
A. You don’t specify if you have one of the native varieties or the Asian import known as the Kousa dogwood, but you’ve already shown yourself to be a better arborist than your arborist by diagnosing the problem as probably being caused by a bad location and not a disease.

Yes, dogwood trees are prone to anthracnose, a fungus that affects many plants, especially in damp, wet seasons. But last summer’s hot and dry weather kept anthracnose problems to a minimum. And your symptoms don’t match. If your tree were attacked by anthracnose, you would have complained about spots and blotches on the leaves, not late arrival (which is normal for dogwoods) or leaf curl—which can be caused by a number of problems but simple-minded me tends to think they curled up because they were roasting in the sun.

Dogwoods are one of those great conundrums of the plant world—they need sun to bloom well, but they also sunburn easily. And they despise drought. And all trees do poorly if they aren’t watered well during their first few years of life. So if you got your tree off to a bad start by failing to water it carefully the year it was planted, it could easily have been weak and behind schedule when that historically hot summer blew through.

Try and figure out which type you have. The native variety (scientific name Cornus florida) is so acclaimed for its fabulous blooms that its common name is ‘Flowering Dogwood’ (even though all dogwoods produce pretty posies), but it blooms the earliest of any dogwood—in April or May, before the leaves appear. So if you’re cleverly pruning it in the summer, fall or winter, you’re cutting off all the buds and that’s the reason for your lack of flowers. The only safe time to prune dogwoods and other Spring blooming plants is right after they flower.

Because the native does bloom so early, its flowers can also be lost to a late hard frost. And you have to be patient; it takes dogwoods a while to settle in before they bloom, and it wouldn’t be unusual to still be waiting for blooms on a three year old.

But no matter which type it is, it doesn’t want to sit out being fried in the summertime. No spray in the world is going to help a plant that’s trapped in a desperately wrong place. Because it’s only three years old, I’m going to suggest we stress it one more time with a move; no fun for the plant, but it will end its yearly heat stress. Replant it in a location that gets full morning sun and some shade late in the day. Not the opposite! Disease prone plants need to dry off first thing in the morning, and dogwoods do tend to get the horticultural sniffles when conditions are poor. (So trading full sun for morning shade would be just as bad as what you have now, but in reverse.)

I suggest you move it now if your ground isn’t frozen yet. The tree should be dormant and there aren’t the distractions of Spring. Follow the directions in our previous Question of the Week on moving plants. When you get the tree to its new location, dig a nice wide hole, but keep it shallow. Dogwoods especially need to planted high in the ground or they’ll develop energy-sucking cankers around the portions of the bark that are underground You must see the root flare above ground or the tree will not prosper. As we recommend with all newly planted trees, refill the hole only with the removed soil; don’t add any soil amendments underground.

Dogwoods thrive in naturally rich acidic soil, so after planting, spread an inch of milled peat moss around the base of the tree, and then cover it with an inch of high-quality yard-waste compost. Don’t use wood, bark or root mulch; those things breed anthracnose like mad! And don’t touch the trunk with any mulch; leave a good six inches of open area all around. But do take the peat moss and compost mulch out as far as the tips of the furthest branches. Water well when you’re done and then provide supplemental water any week we don’t get an inch of rain. Be especially vigilant during hot, dry times.

The tree should thrive once it gets into the right location. To keep it healthy, keep the trunk clear of mulch and debris, don’t feed it chemical fertilizers and don’t use herbicides anywhere near it. But do freshen up the peat moss and compost mulch every Spring—and be sure the compost always goes on top. Compost on the surface of the soil is your best defense against diseases like anthracnose in years when the weather is wet.

Helpful Products from Gardens Alive!

Gardener’s GoldTM Premium Compost - Enriching your soil with compost is one of the very best things you can do for your garden. Gardener’s Gold is 100% all-natural, finished compost. It contains the same organic ingredients you might add to your own compost pile – grass clippings, brush, wood chips and straw.

Shrubs Alive!TM Fertilizer for Acid-Loving Plants - This natural fertilizer is designed especially for plants that require acidic soil, such as rhododendrons, dogwood and pine. Great for blueberries too!

Liquid Kelp Spray - Increases your plants’ vigor and promotes stronger root growth.

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