Blue Oak Early Leaf Browning and Leaf Loss

By Andrea Peck    Master Gardener

My blue oak tree and many others in the oak woodland are browning and shedding their leaves. What is the cause of this and how can I prevent it?

The blue oak is a California native tree that covers the western coast of North America. Named for the bluish tint of its leaves, most apparent during spring flush, it is a sturdy tree capable of withstanding high temperatures and long periods of drought. In appearance, it is generally a medium-size tree with an open canopy. It grows to about 30 feet; however, when provided deep, moist soil, a height of 60 feet is possible. From the beginning, the blue oak spreads deep roots that allow it to survive dry conditions. The extensive root system can tap into water sources through cracks in rocks that are 80 feet down. This strength allows the tree to survive fire and regenerate from burnt or cut stumps.

The blue oak is a deciduous tree that drops its leaves on a predictable schedule. Nights get cool, days get short. Suddenly, November arrives and it's time for the blue oak to prepare for winter and go dormant. Leaves fall.

Some years, however, things just don't go as planned!

During the late 1970's and late 1980's severe drought conditions plagued California. At that time, many blue oaks began dropping their leaves in August―or about three months early. As tough as the blue oak is, it still requires up to 300 gallons of water daily. When water supplies become depleted, to conserve water, leaves turn brown and drop to the ground, much as they ordinarily do in late autumn. The tree, in an attempt to defend itself against an unfriendly environment, goes dormant. This is happening even earlier this year than in previous drought years. Of course, it is also unusually dry this year.

Trees with this mechanism are often coined, "drought deciduous."

Deer are eating my bushes and I have gophers in my vegetable garden. What do I do?

Diversify with Dahlias!

By Christina Muller  Master Gardener

I would like to grow dahlias.  Where do I begin?  Becky, Morro Bay

Dahlias are showy flowers that encompass a wide variety of flower form, size and color. These tuberous perennials range in size from bedding plants to the stately tree dahlia,Dahlia imperialis, which stretches to a height of 12’-15’.  Flowers are incredibly varied, from a petite  2” diameter to the ‘dinner plate’ dahlias with a 12” diameter.  Nearly every color except blue is represented and flower forms include single, double, pompon, cactus, and fimbriated, among others.

Plenty of sun and moist, well-drained soil will suit your dahlias.  They are most often planted as tubers in the spring but can be grown from rooted cuttings as well.  Taller varieties should be staked for support as the stems of dahlias are hollow.  These stakes should be placed 5-6” from the tuber at the time of planting.  If you didn’t plant dahlias in the spring, they may be available now in nurseries as container plants.

The most common pests are snails and slugs.  Hand pick them in the evenings and bait with a product containing iron phosphate which is non-toxic to pets and wildlife.  Earwigs can also damage leaves and flowers.   A shallow cat food or tuna can with some vegetable oil and soy sauce, bacon grease or tuna oil will attract and trap them.  For more ideas on controlling earwigs see the UC pest note: http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74102.html

Dahlias are native to frost-free climes of Mexico, Central America and Colombia and are hardy to USDA zone 8.  In areas with colder winters, tubers can be lifted in fall after the foliage has withered.  Store them in dry peat moss or wood shavings until spring when they can be planted.   Named varieties can be labeled directly on the tuber with an indelible pen.

If you would like to see examples of dahlias in person, plan to attend the dahlia show onWed, July 17 at the Mid-State Fair.  This is a wonderful chance to see their extraordinary variety and learn about them from both judges and exhibitors.

Make Your Plants Happy With Proper Watering  

  
Q:  I go out and water my plants when it gets hot, but they still look frumpy.   
                                                  From  Kay R.  Paso Robles 
  
A:  You need enough water to get to as much of the root system as possible to make your plants happy.  Plants need enough water to properly transport essential nutrients from the bottom of the plant to the very top of the plant. To get water down to the very bottom or edges of your root system, you need to consider the type of soil you have and the depth and spread of your root system.  If your soil is primarily clay, such as that found in North County and in San Luis Obispo, the soil holds more water, so it will retain more water.  Sandy soil, such as that found near the ocean, holds the least water and drains faster. Sandy soil has a penetration factor of about three times that of clay soil so the water seeps more deeply but does not retain as much water as clay soil.  To check the depth of water penetration, dig into the soil and determine how deep the water traveled.  

 The roots of a plant should have access to water at all times, but avoid over-watering and possibly drowning your plants. Watering should be done relatively infrequently, but deeply. The most effective watering should be done SLOWLY.  Quick, overhead watering is not as beneficial to plants.  The best technique is the drip method.  Installation of drip systems is not necessary, although very convenient, but a dripping hose or inexpensive hose timer may suit your needs.   

The root systems of plants vary in depth, so a general rule of thumb is that leafy vegetables and annual bedding plants require 6-12 inches of water.  Small shrubs, tomatoes, corn, and cool season turf grass requires 1-2 feet of water.  Trees, large shrubs, and warm-season grasses require substantially more to reach deep roots.