Friday, February 22, 2013
I just had a call from a gentleman in Sunland who wanted to know what a good pesticide for Mountain Mahogany (Cercocarpus betuloides) would be. I asked him what the circumstances were. He told me that he had several mountain mahogany plants on his property, but the one located in a partially shaded area had been infested with some kind of white-fly or scale for almost six months. He recounted how he had applied a product containing imidacloprid ( a 'systemic' insecticide that is closely related chemically to nicotine) and that had helped but it wore off and the problem is just as bad. I started asking him some questions:
- Q. How often is the plant watered? A. Very little supplemental water.
- Q. Have you fed the plant? A. No
- Q. Have you mulched the plant well and if so, with what?....
Now this last question is a somewhat of a trick question....
He answered that he had mulched his plantings with redwood bark. Mulching is usually a good idea -it helps provide organic material to the soil so that microorganisms beneficial to the plant can increase in the soil. However mulching also produces nitrogen, which can be detrimental to many native California plants...especially plants like Cercocarpus betuloides which have roots that fix the plants own nitrogen.
So what happens when you mulch a Cercocaprus betuloides with an organic mulch that breaks down to provide nitrogen (a plant whose tissues are chock full of nitrogenous compounds to begin with from its own nitrogen fixing activity)? First you get an increase in green, succulent growth which is attractive to insects like whiteflies, scale, aphids etc. that feed on the food conducting tissue, the phloem, of the plant. To make matters worse besides increasing the plants susceptibility to these insects the increased nitrogen content of the sap caused by the mulch actually helps these pests reproduce! So mulching with a nitrogenous mulch is like pouring gasoline on a brush fire for these plants. Unfortunately for my caller, redwood bark is such an organic mulch (although its nitrogen release is delayed and much slower than other organic mulches), and it can even be toxic to some plants under the right circumstances..so what to use?
Decomposed granite (D.G.) comes in many different sizes from fine particles that congeal like clay when they dry to almost pebble sized grains. Since D.G. does not break down to provide nitrogen it is ideal for those California natives that fix their own nitrogen and so might suffer if a nitrogenous mulch is applied. So not only is D.G. a good alternative for nitrogen sensitive plants like Cercocarpus but if you're mulching with the smaller, soil-particle sized D.G. you have a situation that can attract native bees which prefer nesting on bare ground.
Thursday, February 7, 2013
I received a request by phone today for a 'London Pride' Saxifraga and was intrigued by the plants history. Apparently during the dark days of the London Blitz this hardy rock garden plant would be the first to colonize the fresh bomb craters. It's plucky colonization and the rather rapid interval between its appearance and flowering were a source of inspiration to war weary Londoners. It was so inspirational that it inspired a wartime song by composer/playwright Noel Coward.
Finding a London Pride plant however, was a daunting task. It is not carried by local nurseries (it likes dank, moist environments like London and Ireland) and finding any nurseries in the continental U.S. that did carry the plants was impossible. After much searching however, I did find a seed source in Devon, U.K., which was fortuitous because the caller had friends there who could procure them for her.
Tuesday, February 5, 2013
Saturday, February 2, 2013
|Frost damaged mango tree.|
The recent spate of frost has left many local gardeners tropical and semitropical plants looking dismal, decrepit, and destroyed. But now is not the time to clean house and start over. Many times frost damage is far worse looking than it actually is, and many plants can recover from frost damage if you take some simple steps and refrain from taking others. Here is a list:Do not prune any frost damage off of your plants until all danger of additional frost has past. The dead and damaged tissue of a frost damaged plant can act as an insulator, protecting the living tissue beneath from further frost damage.
|Frost cloth like this is specially designed to keep frost off of the plant while allowing air to flow through.|
Purchase "Frost Cloth" and cover your susceptible plants (including already damaged ones) when frost is predicted.
Spray 'Cloud Cover' or a similar anti-transpirent on your plants. These compounds prevent the plant from drying out when exposed to frost. They are harmless to the plant and give you an extra layer of protection besides the the frost cloth.
|Anti-transpirants like 'Cloud Cover' help protect the plant by plugging stomata, the small holes in the leaves and stems of plants, and thus preventing the plant from drying out as the result of frost.|
The above actions should help minimize frost damage until all danger of frost has past (here usually mid-March). After that period is over you may need to re-assess what you are planting and where you are planting it.
Friday, February 1, 2013
Q.Are 'Full Moon ' maples (Acer japonicum) suitable for Southern California? If not, What variety of maple do you suggest? I live in The Rancho Santa Fe area of North San Diego county.
A. I've seen 'Full Moon' maples growing in protected spots or as bonsais here in Southern California. If you decide to grow them you should keep them in pots located in protected areas with filtered shade; also when they grow here their leaves tend to burn starting about mid-summer.
If that's not discouraging enough there’s another problem now –many maple species here are under attack by a pest called the Polyphagous Shot Hole Borer. This beetle has been killing maples here and will probably only get worse, so you taking a big gamble no matter what maple you plant. The pest is currently not in San Diego County but at the current rate of spread may soon be.
University of Conneticut Horticultural Information Page:
Mendecino Maples Acer japonicum selection: