With all the rain that we have been having this year (and it was supposed to be a dry year in San Diego!), designing your landscape with good drainage is a definite must to protect your home.
Living in the desert near the coast like we do, dry and wet years will come and go. When they do, your plantscape must be able to tolerate the extremities of heavy rain and drought conditions sometimes in the same year.
Most good designers will create outdoor “rooms” in the back and front yards. These are spaces that draw you to them, where interest and mystery is created by hiding a “room” behind a panel of vertical plants or a mounding of soil, rock or low wall.
They also usually have a function and serve as the locale for the wet bar, barbecue, pool, fire pit and so on.
When these places are installed, nothing helps the overall impact of the design more than incorporating an overhead or upper story canopy placed strategically in a dividing planter or to create some precious shade for the understory plants and people utilizing the space.
One of my favorite tricks is to use trees that have good movement in a light wind because of the beauty of the interplay between light and shadow; however, the more important design application here is to know the root structure of your larger trees and to know how they will be affected during heavy rains and high winds.
When rain comes, it is usually in many forms. Light, sporadic, continuous and torrential. Most soils can tolerate a quick inch or two, but after that, absorption slows down dramatically.
Most tree failures I see on a common basis are large surface rooted trees placed on 2 to 1 slopes or steep banks. Herein lies the problem, most homeowners recognizing the need, find a tree on sale at Home Depot, plant it on the back bank and forget about it.
Typically a fast growing tree, like a eucalyptus or Melaleuca leucadendron, is chosen because it is cost effective.
The tree grows quickly to the delight of the homeowner (who hates the lack of privacy from his neighbor up above) and is good for a year or three.
Then, the tree starts to grow exponentially because the riser at the top of the bank is either broken or it hits nothing but tree trunk on a daily basis.
Now, here comes an unseasonably wet winter.
The tree in question on the bank hasn’t been trimmed and is topping 30 feet.
The rain comes mercifully and arrives gently with a weeklong soak.
All the plants are loving it but the underlying soils are becoming heavier and softening with the deep saturation they are receiving.
At this point, heavy shallow-rooted trees reaching for the sun on the south side of the yard will begin to move and lift the ground on the opposite side of the lean. This is a dead giveaway for future problems.
As the rain continues, each leaf is coated with water as well as the branches and will increase the weight of the tree dramatically.
Have you ever tried to pick up a large fallen branch in the rain? Good Luck.
And so, as the storm moves in, or moves out, the atmospheric pressure variant changes and we have wind.
The taller the tree, the more leverage it applies to the root ball and the easier it is for the tree to topple.
I once had a client pressure me about triple staking some newly planted 36-inch box trees. They lived on top of a hill and sure enough the wind came with the fires blowing away a large party tent. How were the trees? No problem, they weren’t tall enough.
When you design your upper story canopy, keep in mind these principles. It will save you a lot of expense and heartache. Put smaller patio trees on the steep slopes around your home. Choose small dwarf varieties that have beautiful color and spread out with low branches. Keep in mind that the slower growing species are always the most desirable and that if you just have to have height on the bank, use a flexible bamboo, fibrous deeply rooted palm or a giant bird.
Filed Under: Local Roots