Janice N. of Santa Rosa asks: What are some prevention basics to help a newbie vegetable gardener get a better handle on diseases for next year?

There are three primary vectors for plant diseases: pests, moisture and poor rotation.

Pests: Infestations of garden pests easily and quickly spread fungal spores from sick plants to healthy ones, so staying on top of pest populations will greatly improve the health of your plants through the growing season.

Moisture: If there’s a lot of dampness due to fog, drainage is poor, airflow around plants is limited or if you are overhead watering, there’s a pretty good chance you’ll battle with some diseased plants.

Rotation: If you plant members of the same plant family in the same spot over and over again, you’re asking for trouble by providing a constant food supply for diseases. One of the best methods for discouraging diseases is rotating your crops on a three-year cycle. If you have no choice but to plant in the same place, you may want to read up on companion planting, which makes it harder for disease to spread.

Sanitation: It’s really important to follow these simple rules. 1) Don’t touch a sick plant and then a healthy plant without washing your hands in between. 2) Never prune a sick plant and then a healthy plant without disinfecting your pruners. 3) Bag diseased plants and put them in the trash. Never compost them. Unless your compost pile gets really, really hot, you risk inoculating all your plants when you spread the compost.


Deb Williamson of Santa Rosa asks: I love the look of ivy, but is it OK for it to grow up a tree?

Ivy (Hedera) is planted in many different areas for a variety of reasons. The stems spread quickly and send out small roots that adhere to soil or any rough surface, so once it establishes itself, ivy can become invasive if it isn’t proper pruned on a regular basis.

Many people love the look of ivy gracefully winding its way up a tree trunk, but you should always remove it. Ivy itself isn’t really the problem, but because it helps moisture stay against the bark of the trunk, it creates constant dampness that attracts insects. It also hides any developing problems with the tree. Tree diseases and decay can become major problems because they were hidden by ivy.

If you have a tree with a lot of ivy coverage, eliminate it. Go around the trunk and cut out a vertical section of ivy about 1-2 feet wide around the entire tree. That will cut all the roots to the upper section of the ivy. Remove the cut section, but leave the upper ivy to die. It takes awhile, but be patient. Ivy is much easier to remove once it’s dead.

After that, pull any ivy that is still alive from the base of the tree. This area is the most important because it retains the most moisture and any decay can spread quickly.

Note: Ivy can still be a lovely ground cover around the base of the tree, just not on the trunk or any exposed roots. The ivy will continue to grow, so keep a watchful eye on the base of the tree to keep it in check.

Dana Lozano and Gwen Kilchherr are garden consultants. Send your gardening questions to The Garden Doctors, at pdgardendoctor@gmail.com. The Garden Doctors can answer questions only through their column, which appears twice a month in the newspaper and online at pressdemocrat.com.