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Weigela in trouble


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#1 annem29

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Posted 29 May 2006 - 09:10 PM

We have a mature weigela, about 8' tall. Don't know for sure the variety, but it has bright green leaves and hot pinkish red flowers. Last year, after the very cold winter, about 1/3 of the limbs were dead in the spring, with no leafing or new growth at all. This included limbs all the way down to the ground. We pruned and/or sawed these dead limbs and branches off, and new growth did appear from the base. This spring, the same thing happened to another 1/3 of the original limbs--what was the center of the plant before we had to cut down the branches. This is different from normal tip dieback--this is entire branches and limbs from the tip to the base of the shrub.

My question is: does weigela have a lifespan? Or does it require regular hard pruning for rejuvenation? Should I be doing something to prevent the last 1/3 from doing the same thing? Aside from the *very* lopsided appearance, the plant is fine. It has an abundance of flower buds on the side that is still alive, and does not seem stressed or unhealthy to outward appearance. As I mentioned, it is shooting up new branches from the center. I haven't been able to find any information other than that some winter tip dieback is normal, but this seems quite extreme. Does anyone have any ideas?




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#2 Guest_Margaret Thele_*

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Posted 08 July 2006 - 09:16 PM

What is going on with the root system of this plant? I have seen wiegelas get awfully ratty in their mature and advanced age. What's the soil type? Irrigation ? Mulch? Maybe if we can work out a few more details like sun/shade exposure, competition etc. we can help you get to the bottom of this.
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#3 Janet Macunovich

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Posted 09 July 2006 - 08:42 PM

And it would be good to know if you saw any physical damage at the base of the dead limbs. Rabbits LOVE weigela.
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#4 annem29

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Posted 15 July 2006 - 12:11 AM

I'll try to answer with as much detail as I can:
No rabbit damage is visible, although our yard is FULL of bunnies and deer, and they are fearless. I didn't know the reabbits liked weigela. I'll keep an eye on it for bunny damage, but they seem to be sticking to the perennials! When the weigela was doing better, I had underplanted some lilies of the valley, since the deer don't like them, and they are thriving, even though their shade is depleted. It is in a bed on the northwest corner of the house that gets eastern sun in the morning, and then southern and full western sun for the afternoon. Some shade from the house in late morning. Our soil is no better than average, sandy and well-draining, and I mulch with a shredded hardwood every spring; since it gets a lot of sun, the site tends to dry out quickly. There is lawn on 2 sides of the bed and concrete on two. A very slow-growing pine tree/shrub is about 6-7 feet diagonally away, along the foundation of the garage, and there are 2 large rocks in the bed as well. There is a little foot traffic through the bed, next to the weigela, although I have tried to stop that. There is more foot traffic on the grass side of the plant. I don't really do any special irrigating of any of the established plantings (although I have for this one since it bloomed last month, to encourage new growth.) Typically it got a little water from the lawn sprinkler system, and then rain. I haven't fertilized. It is showing new growth from the base, but more branches are losing their leaves at the same time.

The possible negatives that I have seen: This is NOT a winter protected site, and it gets fully exposed in the winter. But branches that bloomed and leaves that were green in June are dying now, so I don't think it can all be chalked up to winter kill. Also, snow cleared from the driveway ends up on this planting bed, up to 2 or 3 foot piles, all winter. And previous owners (NOT me) used that icky plastic landscape fabric throughout, and it is still present there, under the topsoil and mulch. (That's actually a question for another topic--how do you get rid of that plastic!?!) I also see LOTS of ants around this bed. Since it's adjacent to lawn, it may have received some of the lawn fertilizer pellets around the edges, although he knows that's a no-no. I'm not really sure what else you need to know--sorry I can't be more precise on some of these things. I would appreciate any suggestions or thoughts you might have. Thanks!

Anne



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#5 Guest_StevenNikkila_*

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Posted 17 July 2006 - 04:31 PM

The first thing I would do is remove that plastic! It is doing no good for the soil or the plant. The plastic prevents the mulch from breaking down and it causes the soil to become compacted because it dosen't allow for good air and water exchange. To remove the plastic rake off the mulch, scrape off the topsoil and pull the plastic off the bed, you may have to cut it around the plants and this will take time, but it is time well spent. Then replace the soil and mulch but only 2 to 3" thick, I suspect it was probably thicker than that. You can use the excess in other areas.

Then change where the snow is piled up, if possible. If that snow is from the driveway it may have salt in it and excessive salt my cause damage plus pushing the snow may damage the shrub.

Water the bed well and prune out the dead wood and watch the plant.
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#6 Janet Macunovich

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Posted 19 July 2006 - 03:49 PM

Hi annem29!
You write:
"But branches that bloomed and leaves that were green in June are dying now, so I don't think it can all be chalked up to winter kill"

To the contrary, much winter damage DOES show up in midsummer. It's a classic!

When the outer layer of wood, the cambium, is damaged by animal chewing, freezing, borers, snow load breakage, etc., a plant may leaf out and seem to do fine at first, because the water that fueled leaf growth comes up to the leaf buds through the inner wood, not the cambium. But then those leaves can't properly feed the roots, as is their job, because the cambium is patchy with damage. The only place leaf-made starch can move down to roots is through the cambium.

So a plant may grow along looking okay on top during spring, yet its roots struggle, unable to grow. Unable to tuck away any starch against a bad day because all the little bits of starch that make it down to the roots are needed immediately. The roots may reach the end, finally starve to death, when summer heat comes and the leaves shut down on a hot day (wilt is a defense mechanism; but a plant in wilt can't photoynthesize). The roots die then because they were living day-to-day and have no starch reserves to tide them over. Once the roots die, then the leaves go next, quickly. Foliage just wilts and then dies, because without living roots to bring water into the system, there's none there for the leaves' use.

This may well be a hardiness issue. It could be that, given that west-facing site, winter alone accounts for this. But there may have been site change, too. Has anything nearby changed-- like a hedge or a tree on the west or northwest being removed recently, or dying, thinning out? Because west-facing and southwest-facing parts of plants have the worst hot-to-cold changes to deal with on sunny late fall and late winter days. That effect would have been made worse if something that used to shade the plant is goen.

And consider this: the LAST part of a woody plant to become hardened off in late fall is the base of the stem. The cellular adjustments against freezing start at tips and work down. Thus roses that die over winter often have split bark right at the stem bases/soil line. Once it got cold those bases just exploded, too full of water to handle the temperature change.

If the shrub used to have more time to harden in winter, because it had a bit more protection, or was a bit healthier for other reasons -- it may have been able to harden off, once upon a time. Now it may not be able to. Exposure/inability to harden in fall would account for the dieback being primarily on one side, which your comment about one-sidedness seems to indicate.

Paradoxically, the long, warm falls we've had have not been kind to marginally hardy plants, some of which are not receiving in time the "it's getting colder" cues they need to harden off their wood for the cold.

One test might be to mound soil over the base of this weigela once a hard frost comes this fall. Just like for roses. For the best test, mound over one quarter of the base -- half of what's been involved in the damage up to now. Then next spring, remove the soil and watch. See if that half that half of the previously-dicey canes make it through summer.

By the by: Rabbits, those on my turf, LOVE weigela. Two years ago they pruned a whole hedge, ten weigela, taking every new cane to the ground.
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