Growing Concerns 549: Rhododendrons, care, girdling root

Early Winter!

Rhododendrons need extra care since they rarely put down roots in northern soils soils


 Dear Janet,

Early last summer I planted a rhododendron. It seemed to do well where it was, near the house on the northwest side. However, my dog just pulled it out of the ground! I was surprised that the roots had not grown enough to anchor it. My soil is heavily clay, although I had dug a large hole and mixed in some peat moss to loosen it up.

Is it common for the roots to not grow much? What do I do with it now? I was thinking I shouldn't put it back in the same hole now that it's so cold, since apparently it didn't take too well to the location. Should I just put it in a pot and keep it cool until I can replant in spring?


Dear J.,

A tree or shrub's roots should grow as much or more as its branches each year. However, acid loving plants such as rhododendrons tend to grow poorly in southeast Michigan's alkaline soils. I've seen many with root balls the same size or smaller than they had at the nursery, even after years on site.

So your shrub is on par with most rhododendrons in our area. You can keep it in a pot in a cold garage and relocate it in spring. But if it was growing foliage where you'd placed it and that spot is sheltered from wind, you can put it back in the same hole.

Since you know what a tiny root ball it has you will know how important it is to keep it watered during dry thaws. Mulch it two to three inches deep with acidic materials such as pine needles, cocoa hulls and coffee grounds. Once the shrub begins to grow new leaves it will root into that acidic layer, so keep renewing the mulch and don't plant any competing groundcover there.

Fertilize regularly from April through July with a water soluble fertilizer for acid-loving plants. Sprinkle the solution on the leaves as well as on the root zone, since both can absorb those nutrients.


 Dear Janet,

I had a Norway maple that died. After declining for about two years it just didn't leaf out the third year. The tree specialist said the cause was a girdling root. He said he knew because the trunk was squareish. Is that truly a way to diagnose that?


 Dear R.,

The Norway maple is famous for wrapping a root around and then strangling itself as thickening root and expanding trunk run into one another. Symptoms often appear as the tree reaches 15 to 20 years old -- growth slows, the center top of the tree may die back, and yes, the side of the trunk that's being prevented from growing becomes increasingly flat.

As Dan Kurkowski, Forester,  explains it, "The total lack of root flare is a definite 'telltale' of girdling roots. The trunk will go right into the ground like a stovepipe."

Winter is a good time to take a look at your trees and see if they have a healthy flare all the way around the base or are flat on one or more sides. A girdling root that's caught early can be cut away. You saw two years of decline before your tree died but it's likely it was growing less well and showing trouble for ten years or more, during which time that flattened side would have been a flag to one who can read trees.


Green thumbs up

 to being sure before you water that a plant has used all excess moisture in its pot. Thirsty pots are lightweight or feel dry on the surface. Since plants use water only if they have light to photosynthesize, they use very little in these dark, short days of winter. Overwatering, with attendant root rot, kills more plants than underwatering!


Green thumbs down

 to that every-year trampling of the same places under trees and in foundation beds where you walk to put up and take down holiday lights. Packing down the soil over plants' roots leads to long term trouble like toppling and susceptibility to root diseases. Take note this year of trampled ground and loosen there with a garden fork in spring.

Originally published 1/10/04