By Urban Harvest
Newcomers to the Houston area are often struck by the abundance of critters flying and crawling about.
The main reason for this is that we have plenty of rainfall and warmth year round. Further west, drought stops most pests, and further north, freezing temperatures do. We can garden year round because of the regular rainfall and warmth, but we pay with humidity in the summer and lots of pests.
Frequently, gardeners confronted with something bothering their tomatoes or their roses ask me “What pesticide should I use?” Firstly, using chemical pesticides on food crops is not a good idea since chemical residue is not easily washed off. Also for several reasons pesticides do not easily stop our pests here. Most pests breed quickly and are adept at hiding, so it is hard to reach all of them with a sprayer.
Also, our abundant rainfall washes the pesticide away from where it was put hours after a spray. Pesticides often kill the pests’ natural enemies as easily as they kill pests, so even when the spray is the correct one correctly applied, it may still lead to an increase in pests later on. Thus, homeowners with a spray program do not easily achieve cost-effective pest control.
Rather, plant pests and diseases are more easily and cheaply stopped by their natural enemies —predatory insects, birds and other creatures, parasitic insects that lay eggs in pests, and soil microorganisms that destroy soil pests. So the best strategy is to invest in landscape design elements that favor the abundance of these pest-destroying creatures.
There are six strategies for suppressing pests: diversification, keeping plants healthy, encouraging pests of the pests, using barriers to keep pests from plants, trapping pests, and using low-toxicity highly specific pesticides. If one looks however at total costs, results, and hours of labor over a period of five to 10 years, the list above starts with the most effective, cheapest, easiest strategy and ends with the most expensive, hardest, least effective strategy.
Diversify Your Landscape
The first strategy one should consider is to diversify the landscape. The old saying about all the eggs in one basket is particularly true with gardening. A garden where almost all the plants are one thing — oak trees, turf grass, azaleas, or tomatoes for example—is one that is highly vulnerable to pests. Diseases and pests do not attack all plants equally, but typically go after plants in a particular horticultural family or one particular species or even a specific variety of the species. That’s why different tomato varieties come with VFN ratings and oak wilt has the word oak in it.
Also, pests and diseases mainly attack weak unhealthy plants. If you mainly grow a whole lot of a few kinds of plants, and one year it is too wet, dry, hot, or cold for that plant, you have created perfect conditions for those plants’ pests to breed — weak plants and plenty of food. So you have a bug plague and a lot of dead or sick plants.
By contrast, if you have many different kinds of plants in the landscape, with duplicates spread out rather than grouped, you minimize the likelihood that most of your landscape will get sick all at one time. A landscape with natives, trees, shrubs, shady and sunny areas, damp and dry habitats will moderate whatever our climate, pests, and diseases decide to do. Diversification isn’t necessarily cheap since it requires plant purchase, nor is it easy work to plant and establish a landscape, but once the diversification is established, ongoing maintenance and cost is the easiest and cheapest of anything you can do to control pests.
Healthy plants resist pest attack. Garden books and classes are full of advice on how to have healthy plants. I often say that taking care of plants is similar to taking care of pets: dogs, goldfish, and horses all need to be fed, but just knowing that won’t get good results. To do well, you need to know what each pet or plant needs. You know this either because someone taught you or you read about it in a book, and you have hands-on experience. Plants will be healthy if they get the kind of drainage they specifically need, the kind of soil, the kind of surface organic matter, the kind of moisture or lack of it, and much more. Annual plants (that live and die in the same year) must be planted when the soil and air temperatures in the next months will be right for seed sprouting, growth, and fruiting. So for annuals, local planting dates are crucial. Perennial plants (that must live many years) must stand the highest winds, the wettest soils, the longest droughts, and coldest deep freezes, so finding the best variety for our area is crucial. The only way to do this is to get good lists from books or classes by those with decades of experience here.
Encourage Creatures that Eat Pests & Diseases
There are several things you can do to encourage creatures that will eat or parasitize pest insects and diseases. Make sure there is always a supply of fresh water such as a birdbath in the yard, have a large perennial flowerbed that provides cover and shelter for toads and lizards year-round, mulch everything with rotting leaves or shredded composted tree branches, and avoid using toxic substances. Grow a diversity of Houston area native flowering plants, since native beneficial insects are attracted to native flowers. As well, be sure to grow plants whose flowers attract adult beneficial insects. These beneficials are often very picky about which flower nectars they can use, but if they find your yard and like it, they will “start families” by laying eggs in your pests, and these when they hatch will dispatch your pests.
Especially important plants are cilantro, fennel, Italian flat-leafed parsley, mint, salvias, buckwheat, and Carolina buckthorn. The fall is the best time to be planting all but the last two of these plants. If you would like to get a head start on your fall gardening, think about taking the Urban Harvest July 23 class, Fall Vegetable Gardening. Register online at www.urbanharvest.org or call the office 713-880-5540.
This column is produced by Urban Harvest. Learn about gardening classes, community gardens and orchards, farmers markets and more at Urban Harvest website. The article is written by Bob Randall, Ph.D., who is the former executive director and a cofounder of Urban Harvest. He is also the author of "Year Round Vegetables, Fruits and Flowers for Metro-Houston." You may contact him at YearRoundGardening@comcast.net.