Monday, December 8, 2008

Remedies for the "Green Wall"

When large, evergreen shrubs are planted in landscape beds right next to the foundation of your house, they frequently end up blocking windows, entries, or pathways with a "green wall". Rhododendrons and Camellias are often the culprits in these cases for several reasons: they've been very popular as foundation plantings for many years, it's hard to imagine them at 6-18 ft when they're purchased in pots, and the walkways of many homes are built so close to them that it creates a very narrow garden bed.

The green wall can be frustrating for several reasons: having your garden view and sunlight blocked, rainwater dumped on you when brushing past, or feeling that the approach to your house is unsafe. The urge to do some major pruning on the "offender" can be pretty strong.

However... the green wall will get worse quickly if large heading cuts are made on branches, which stimulates immediate growth in all directions. Leaves are a plant's "food factory", and this is its survival response in order not to starve to death. So the result is that instead of 1 or 2 branches in the way, you may end up with 8! Genetics determine the plant's mature size, which it will continually strive to reach no matter what we do.

The art of pruning does have several solutions that work with the plant's nature instead of against it. (always more successful than just ordering it in vain to "halt!") Making thinning cuts to branches modifies the green wall, yet allows the plant to grow to its mature size and retain its basic natural form. However, if the plant is in need of serious rehab, the thinning may need to be done gradually over the course of 1-3 years in order to keep the plant in good health.

If you live in the Seattle area, I'll be glad to schedule a pruning lesson to help you get started on implementing any of the following solutions:

1) Plants growing in front of windows can be thinned throughout their framework, retaining their height, but creating a pleasant and safe view through their branches.

2) Plants blocking pathways or entries can be thinned to have a tree-like structure from ground level to 7 ft. At that point, they can be allowed to grow to their full width.

3) Another solution for plants blocking pathways is to thin the depth of the plant's structure throughout to create a fan-like form. This allows the remaining branches to reach full height and width, and creates an informal espalier.

The first step in any pruning strategy is to remove excess deadwood, which is usually clogging up the interior of the shrub. You'll be amazed at how much more beautiful the plant looks immediately, and its simpler structure also makes it easier to decide which live branches to remove in order to achieve the end effect you want. See the Fall Garden Task blog for a detailed description of how to successfully remove deadwood.

I recommend pruning off no more than 15-20% of the shrub's total live leaf canopy in any 1 year period. Many books recommend 30%, but I disagree. You may be able to get away with doing more than 20%, but remember that you may not... so only take that chance if you are willing to take the risk of serious plant shock or worse.

Years ago, I learned a great tip from Cass Turnbull, founder of Plant Amnesty, a great non-profit pruning education organization. To make sure you are not removing too much live growth, always pile up your prunings near the shrub instead of stuffing them into the yard waste bin right away. That way, you can easily keep track of the size of the pile in comparison to the shrub, and you will definitely lessen your chances of removing too much!

Rhododendrons and Camellias can be pruned most any time of the year, but doing it now will cost you some of this year's flowers. It's just fine to prune during bloom and bring the flowers inside to be enjoyed, or to prune immediately after blooming is finished.

Last but not least, remember that Rhododendrons and Camellias have a very shallow, fibrous root system, and therefore need more frequent watering than deep-rooted plants, yet still need good drainage. If they are under the eaves of your home, they may need supplemental water even in winter. They can also suffer root suffocation if more than 1-2 inches of mulch is put around them.

This type of root system also means that even large Rhododendrons and Camellias may be able to be moved to another place in your garden, where they can grow to mature height and width without being in your way at all!

Or, how about moving the walkway out further from the house in order to create a generous-sized planting bed?

Another source of pruning ideas is Plant Amnesty's flyer entitled "My Rhody's Too Big", available by calling 206-783-9813 or through This helpful organization also has pruning flyers on everything from Abelias to Wisteria, and a wonderful series of pruning classes. Consider becoming a member so you can receive a discount on pruning classes and get to attend their fabulous member potluck "Meeting of Like Minds" events!

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