Ask the Garden Sage

Garden Guru: Ensuring your plants don’t promote wildfire

2014-05-25T00:00:00Z 2014-07-03T12:04:22Z Garden Guru: Ensuring your plants don’t promote wildfireBy Peter Warren Special to the Arizona Daily Star Arizona Daily Star

This is the debut of a gardening column that will appear twice a month in the Star’s Home + Life section.

Q: I live just outside the city and I have a lot of desert vegetation in my yard. How can I tell if my plants are putting me at risk if there is a wildfire nearby?

A: All vegetation is potential fuel for fire. The type, amount and arrangement can have dramatic effects on fire behavior. The most important factor is moisture content, although some plants have resin content that makes them flammable regardless of moisture content. Deciduous plants tend to be more fire-resistant because leaves have more moisture content.

Characteristics that make plants more resistant to wildfire include growth without accumulating a lot of leaves or needles; open, loose branches; low resin content (many deciduous species); high moisture content (succulents and some herbaceous plants); slow growth without frequent pruning required; and being short and close to the ground (wildflowers and ground covers).

Widely spacing plants nearest to your home; planting in small clusters rather than large masses; using a diversity of species; and breaking up the vegetation with rocks, gravel and pathways are ways to design a fire-wise landscape.

Q: I have prickly pear cactus that has white patches on the pads that looks like little bits of cotton. What is this, and is this bad for the plant?

A: Most likely what you are seeing on your cactus is an insect called cochineal scale. These insects cover themselves with a waxy coat that appears like white, cottony tufts. To verify this is what you have, you can crush one of them to see if it leaves a bright, red stain. This red material is the blood of the insect, and its color is due to the presence of carminic acid. Humans use this to produce carmine dye for various things including food coloring and lipstick.

Scale insects insert their mouth parts into the cactus to feed on the sap, and over time can reduce the vigor of the plant. You can help your cactus by spraying the insects with a hose periodically and/or using insecticidal soap.

Q: My neighbor has his agaves pruned, and now they look like giant pineapples with only a third or less of the leaves left sticking straight up in the air. Is this a good way to prune agaves?

A: Pruning in general should only be done when necessary, such as when there is damage to the plants or if there are safety considerations. Without knowing your neighbor’s intentions, I would say it is not the best way to care for agaves. Typically we want agaves to achieve their natural shape and prune only damaged leaves.

Wounds from pruning can let pests infest plants, and it is always stressful for the plants to recover from wounds.

Peter Warren is the urban horticulture agent for the Pima County Cooperative Extension at the University of Arizona. He directs the Master Gardener Volunteer Program, and works with landscape professionals and homeowners to promote integrated pest management and best management practices for desert horticulture in Southern Arizona. Questions can be sent to plwarren@cals.arizona.edu

Copyright 2014 Arizona Daily Star. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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