Wednesday, May 29, 2013

Why Do My Palm Leaves Look Like An Accordion?

The leaves of this palm look like an accordion; why?
Today I came into my office and noticed this waiting for me; the distorted leaf of a king palm with a note placed nearby wondering why the distortion was present. After some research and a discussion with palm expert Dr. Don Hodel (who coincidentally happened to be visiting us today) I have somewhat of an explanation.

The most common reason for this kind of disfigurement on palms is a lack of boron. Essential for the growth of palm trees, boron is fairly common in the soils of Southern California. Even though it is practically ubiquitous there are certain cultural factors that can prevent if from being available to the plant. If the soil is too acidic boron will easily leach out of the soil; one way to do this is to fertilize the lawn surrounding the palm with Ammonium Sulfate, a type of nitrogen source that can acidify the soil its applied to; another way to inadvertently raise the pH would be to keep the area to moist for a period of time -constant moisture and lots of organic material in the soil can lead to an anaerobic and acid condition. But ironically another condition that  can make boron unavailable is soil that is heavy clay and too dry. With the preceding condition the boron becomes bonded to the clay particles and becomes unavailable to the palm.

The first remedy is to find out what physiological or cultural condition is causing the boron deficiency and fix it. Check the drainage around the plant, after a rain or a heavy watering look for water that puddles and doesn't disappear for a while. Check the pH of the soil too with a kit (you can buy these from your local garden center or on the web). Finally, there's the '20 Mule Team Cure'; 2-4 ounces of household borax added to 5 gallons of water for each medium sized palm tree. Make sure to keep the solution agitated because borax doesn't dissolve very easily in water (remember using borax to wash you hands back in the day?).  Err on the side of less rather than more because borax in higher concentrations is an herbicide.

But its not just boron that can cause accordion leaf; anything that adversely affects the main growing point of the palm, the apical meristem, can also cause it as well. This means diseases like pink scale, a fungus that shows up on palms planted in poorly drained areas with poor air circulation, and herbicides can cause the problem too. So make sure to rule out all these causes before you start applying borax to your trees.

Web resources:

Descriptions of boron deficiency:

This document discusses the '20 Mule Team' cure:

Saturday, May 25, 2013

Mildew's and Don'ts

June gloom is here; always a welcome respite from the erratic heat waves of May but a month that can be a problem for plants susceptible to the mildew fungus. I’ve composed the following do’s and don’ts to help your garden remain as free as mildew as possible.

Do select and grow mildew resistant plants. Roses, Crepe Myrtles and other plants that are notorious for harboring mildew usually have varieties that have been selected to resist the powdery white scourge.

Don’t fertilize. Nitrogen based fertilizers increase susceptibility to mildew
Do use copper dormant spray on deciduous plants. These sprays will help kill mildew when it germinates in spring.

Do wash the plants foliage; mildew spores cannot germinate on the ground, so wash them off during mildew season, however do not use this method if you have other fungi infesting your plants (like rust) that are spread by water.

Don’t allow weeds and un-composted leaf litter to collect around susceptible plants (this is good advice for all plants).

Do use simple, organic methods of control (see below).

Don’t let mildew get you down; it’s an obligate parasite which means it needs its host alive to survive. At worst it will stunt your plant but it almost never kills plants.

Paper on stomatal density and powdery mildew infestation:

Organic Mildew Treatments
The Cornell Baking Soda Formula and other controls:

Milk Spray: 9 parts water to one part milk; probably works by clogging stomata so that the fungus can't enter the plant. It's reported that skim milk works best.
Neem oil can have a preventative effect on mildew, but I've had too many reports of plants burning from its use to recommend it.

Wednesday, May 22, 2013

Canary Island Color Here at the Arboretum

Limonium, commonly known as statice or sea lavender, is in bloom now in the Arboretum’s Canary Island collection.  This plant, a member of the Plumbaginaceae family, originates from the Canary Islands, a Spanish archipelago off the northwest coast of Africa better known for the sun and sand of Tenerife and the Gran Canarias than for its unique endemic flora. These islands form one of Spain’s autonomous communities and enjoy a subtropical climate with long, warm summers and moderately warm winters.  

Right now you can see large flowering specimens of tree limonium (Limonium arborescens), a tough perennial herb grown from a woody rhizome, a modified subterranean stem usually found underground which often sends out roots and shoots from its nodes.  The flowers are unusual in that they have lavender sepals, the outermost whorl of parts that form a flower.  In most other plants, sepals are usually green and typically protect the flower in bud and often support the petals when in bloom. Its these sepals that make the Limonium inflorescence so spectacular.

Limonium arborescens (foreground) blooming in the Canary Island exhibit. 

A similar looking and commonly available Limonium is Limonium perezii, known as Perez’s sea lavender; also a Canary Island native.  L. perezii blooms nearly year round but heaviest in summer.  The foliage grows to about 18” on a 2 foot clump, with flower stalks about 2-3 feet tall.  The calyx, the outer papery envelope, is rich purple; the corolla, the inner part, is white.  The plant is drought tolerant and, once established, needs only occasional watering.  It grows best in dry, well-drained locations.  Clumps should be divided every 2-3 years in early spring.

Less widely available are Limonium found in other colors.  L. platyphyllum, native to central and southeastern Europe, has a white calyx with bluish corolla.  Even pure whites and pinks exist.  L. sinuatum, a Mediterranean native, comes in even more colors:  yellow, apricot, orange, peach, and rose in addition to the usual blue and lavender.

Most Limonium do well as cut flowers and their papery nature makes them prized for use as dried flowers.  They keep their color well whether cut or in the garden.

Wednesday, May 8, 2013

Plant Identification Links

Links for Plant ID Class

List of conifers and hardwood trees native to North America.
Full on University of Wisconsin course on plant identification and classification.
Very browsable list orders, families, genus and species with example photographs. Also includes usefull family key.
Gives you an idea of when plants evolved and what they are related to.
You can go through to genus starting from the kingdom Plantae.
Read the history of European plant classification.
Review terms you already know and learn new ones.
Part of, a great site for plant science and botanical ‘gee-wizz’ facts.
If it isn’t on this list, it isn’t. Includes links to online herbariums and the International Plant Name Index.
Another interactive key for finding families; a little easier to use than the one on
Mostly good for grasses
More of a poster that has some of the most common families identified by ovary position.
This is the source of our plant handouts.

Video Lectures

Various recorded video llectures on plant science and taxonomy.