Plants are dormant, it's time to prune

By Rebecca Jepsen
for the Mercury News
February 6, 2009

Just because plants are dormant right now doesn't mean we can be.

It's time to prune dormant deciduous plants such as flowering vines, fruit trees, roses and grapes.

But before you get started, choose the right tool to save time and those overly worked muscles in your hands.

Pruning shears work best for branches up to three-fourths-inch in diameter.

Loppers work well for branches from three-fourths-inch to an inch thick. For anything larger, you will need a pruning saw.

Pruning now offers many advantages. Not only does it stimulate new growth and helps wounds to heal more quickly, but in winter there is less threat that diseases and insects will find their way into the cuts.

Pruning helps fruit trees develop a strong framework on which to support a heavy fruit production.

Improperly trained trees will develop upright branches that break under the load, and also can shorten the life of the tree.

Annual pruning should be done to remove dead, diseased, or broken branches.

In general, pruning cuts can be grouped into two primary categories.

Heading is the removal of part of a branch or limb. Heading cuts (topping or tipping) are used to invigorate growth.

Topping vertical branches encourages vegetative growth and tree development.

Tipping horizontal branches is done to renew fruiting wood and thin off excessive buds. New growth occurs where you make the cut and affects only the buds within one-eighth-inch of the cut.

Thinning is the removal of an entire shoot or limb. Thinning cuts are used to remove growth and open up the center of the tree.

Opening up the tree's canopy allows light to penetrate throughout the tree; this is essential for flower bud development and optimal fruit set.

It also allows for good airflow, which will reduce disease and pests problems.

With regular pruning you can also control the size of your tree; something you will appreciate when it comes time to harvest.

How can you tell if a limb is dead when there are no leaves?

All trees form their buds for the following season during the summer months. Fresh buds stay fairly green even during dormancy; dead buds will be dark brown or black.

You can lightly scratch a section of the bark to expose the inner layer, which should be moist and greenish if the limb is alive.

Peach, nectarine, grape and kiwis bear vigorous fruit on last year's growth; remove 50 percent of new growth annually.

Fig, olive, walnut, chestnut, pecan, almond, cherry, persimmon, apple, pear, plum and apricot are less vigorous; remove above 20 percent of new growth annually.

For citrus trees, it's most important to keep branches pruned up and off the ground to deter pests and disease.

Be sure to wait on pruning citrus trees until the chance of a freeze has passed.

For detailed information and diagrams on pruning techniques go to homeorchard.ucdavis.edu/general-pruning.html.

Also check out the Master Gardeners' Web site for pruning classes being offered this month.

Q My orange tree and lemon tree are producing fruit, but a lot of their leaves are turning yellow. Is this a problem, and if so, what should I do?

A Yellowing of leaves and leaf drop can be caused by several factors, the most common being nitrogen deficiency.

Citrus requires a pH of 6.0 and 7.5; proper levels are essential for fruit set and retention. Once the weather has warmed you can use a home pH kit to test your soil.

March is an excellent time to begin applying nitrogen-based fertilizer to encourage new leaf growth and fruit production.

Nitrogen is available in many forms. Follow the instructions and apply only what you need.

Not recommended are highly soluble types such as ammonium sulfate or ammonium nitrate, which can be easily washed into creeks and drains that flow to the bay, polluting our water.

A good indicator of the health of your tree will be how well it produces the first flush of new growth in the spring.

This month you should be enjoying the fruits of your labor from many varieties of oranges, mandarins, lemons, grapefruit, kumquats and even limequats and orangequats.

For a list of recommended varieties for our area, click on www.mastergardeners.org/picks/citrus.html.