How Now Brown Tree?

January 12th, 2013

Jay Rubin’s dawn redwood… temporarily browned.

  Jay Rubin got worried when one of the two young dawn redwoods in his Hampden Twp. back yard turned brown last summer as the thermometer soared to triple digits.   Some 70 percent of the needles on the elegant conifer browned and dropped, even though Rubin says he was “vigorously watering” it for 2 weeks prior.   It’s been the kind of thing lots of gardeners have seen happen as our summers sizzle hotter than ever.

   Especially perplexing is how some of the browning still happens even after we’ve had several soaking rains.

   Blame it at least in part on intense heat.

   While parched soil is a more obvious plant-killer, near-triple-digit heat alone can cause botanical suffering even when soil moisture is good.

   Particularly susceptible are woody plants planted within the past 2 or 3 years and species native to cooler climates.

   Searing heat is enough to cause hydrangeas to wilt.

   It’s enough to fry the leaf margins of shade-preferring perennials.

   And it’s enough to brown whole sections of northern-pedigreed trees, such as sugar maples and Norway spruce.

   Rubin’s dawn redwood, for example, would be a lot happier in its native Chinese woodlands than in our Dallas-like ovenlands.

   A good sign is that this particular dawn redwood started to push fresh green needles soon after late-July rains knocked temperatures back into the “cooler” upper 80s.

   Other gardeners might not be as fortunate.

This spruce is a goner.

   When needled evergreens turn brown, they’re often already dead.   Think about how a Christmas tree stays green for 4 to 6 weeks even after its roots have been totally disconnected.

   That’s the answer to the mystery query, “How comes my tree browned out after the hot, dry spell passed?”

   Reason: It died during the dry-heat spell but took weeks to show it.

   Leaf-dropping trees and leafy perennials are better equipped to deal with heat than some of the needled evergreens that just don’t see 100 degrees in their genetic homeland.

   Deciduous trees (ones that drop foliage in fall) and herbaceous perennials (ones that die back to the ground over winter) have a few heat- and drought-survival tricks up their summer sleeves.

   They can wilt or curl their leaves to reduce the surface area exposed to hot, drying winds, and in extreme cases, even shed their leaves altogether. Then they grow a new set when conditions are more favorable.

   Going through two growing seasons in one year isn’t a good thing, but assuming the ground isn’t so dry that the roots die, the plants will bounce back.

   That’s what happened with Rubin’s dawn redwood. Although this tree looks like an evergreen, it’s actually one of the few needled trees that drops its foliage in fall (making it a “deciduous conifer,” if you’re keeping score).

   Browning from heat is a little more forgiving than browning from dry soil.

   Dry soil kills roots, and without roots, the plant is toast.

   Plants with living roots and heat-scorched foliage at least have a shot at clawing back to life.

   So don’t be too quick to give up — no matter what you’ve got that’s browned.

   Give your browned plants some time to sort out the root cause of the situation.

   Some may still push out new growth a few weeks later — at least on some of the branches.

   Other apparent goners sometimes surprise by re-leafing the following spring or by pushing up new shoots from the roots of the dead top growth.

   A telltale sign in the meantime is the brittleness of the branches.

A branch that’s failed the bend test.

   A branch that dropped leaves or needles but that’s pliable and showing green when you peel back a little of the bark with a blade still has some life in it.   A bare branch that snaps when it’s bent and that shows no green under the bark is dead. At that point, your evergreen has become an everbrown and is a candidate for replacement.

   There’s not much we can do about temperatures that flirt with the century mark. But we can keep the soil consistently damp down in the root zone so those roots stay alive.

   Water also cools, which mitigates the sun’s root-broiling effect. So does keeping 2 or 3 inches of wood or bark mulch over the soil.

   Erecting a burlap or screen barrier to block afternoon sun can help at least your smaller heat-sensitive plants.

   Avoid spraying, pruning and fertilizing heat-stressed plants.

   In the long run, though, it may be worth thinking about moving your most-baked specimens into cooler, shadier spots — especially recently planted bushes, young trees and perennials.