European White Birch-Clumps

Question from Darla:
I just read you response to someone regarding their birch trees.  I had planted yesterday, for the second time, three European White Birch-Clumps at the side of an apartment building in a coastal area of Southern California.  Previously, I lost five trees on the East side of a two story building (two city approved trees on the parkway and three birch in the small lawn area).  I lost all trees within a few years.  I had just removed the last birch stump and it appears there was root rought.  After reading your response to another birch grower, you mentioned moist soil and an adequate water supply.  I noticed that the sidewalk adjacent to this area holds water for several hours after the sprinkler system has ended.  I guess my question is, how much water is too much.  I really want my birch trees to be successfull this time.

Answer from Pat:
Though Sunset Western Garden Book correctly states that European white birch (Betula pendula) will grow in Zone 24, it often succumbs to borer attack. People love this tree because it reminds them of the east coast and is very pretty in front yards. Thousands are sold in Southern California. A few of them survive for a few years, and thousands more die, usually after a few years. So how much water is too much? Here is the answer: European white birch needs regular irrigation, so in well-drained soil, watering with as much as 2 inches or even 3 inches of irrigation per week is never too much, but if the tree is planted in an area with poor drainage, then even 1 inch of rainfall or irrigation water is too much. If you have planted your new trees in a spot with poor drainage your chances for success are slight, and you are between a rock and a hard spot. If you water with less than an inch of irrigation per week your trees will die or do badly and eventually succumb to beetle attack. If you water with more than one inch, and there is no drainage, then your trees will die from root rot.

Another factor affects the amount of water plants need and that is the type of soil you have. (See pages18 to 23 in my organic book that discuss soil problems and pages 36 and 37 of my book for information on irrigation.) Note the “Rule of Thumb” in italix on the bottom of page 37: “One inch of water will penetrate sandy soil about 12 inches, loam about 7 inches, and clay soil only 5 inches, perhaps less.” If you planted in clay soil without proper attention to drainage, you could be soaking the top layer of the soil while roots are dry at the bottom, or alternatively you might be allowing the planting hole to fill up with water and rot the roots since it has no escape route. A tensiometer would let you know the depth that water has penetrated, but if water is not draining you need to fix the problem.

Your best solution would have been first test the drainage and fix it if necessary and then plant the trees. Since you planted your trees last week, it’s not too late to dig a sample planting hole three feet away from the trees and of the same depth as you dug for the trees last last week and do a drainage test as described in the box on page 40 of my book. But if water is left standing in that spot after the ground is irrigated, you already know it has bad drainage. My opinion is you had better dig up the trees, and either mound the soil, or build a raised bed and plant the trees in a raised bed. (See page 41 in my book for details.) Also, if you have clay soil, throw a few coffee cans full of gypsum into the bottom of the planting hole and dig it into the ground on the bottom of the hole. If poor drainage is due to compaction caused by alkalinity of clay soil, adding gypsum to the soil will help improve the drainage. (See pages 21 and 22 for complete explanation.)

Finally, please think again of the description I wrote to another reader about a perfectly planted and well-grown grove of European birch trees (Betula pendula) in Brentwood. Note they were growing on mounded soil but the soil was well-drained decomposed granite. I once saw another, though smaller, picture-perfect garden planted in a similar way on a hill in Zone 23, within view of the ocean. The trees had no protection from the west sun or wind and the soil was clay. The owner of the house was an excellent gardener, but in this case, after about six years the trees died. He wisely did not try again with more white birch. This time he replaced them with a subtropical flowering tree, better adapted to our climate. He chose a red African tulip tree (Spathodea campanulata). It’s now a magnificent specimen that flowers massively for several months in summer and fall every year.

If your birch trees die, you might replace them in that narrow spot with a grove of paperbark trees (Melaleuca quinquinervia), not one of my favorite trees but usually a caste iron plant for difficult situations.