How to keep weeds, pests, diseases at bay

Here are some tips on how to keep your garden and containers looking their best this summer.

Trees can be weeds

My definition of a weed is a plant that’s out of place. A good time to weed is when the soil is moist — the roots come out more easily. It’s very important to get weeds out before they go to seed. A small hand weeder or trowel is helpful. Keep an eye out for tree seedlings such as buckthorn, mulberry, and boxelder that tend to establish themselves in hedges and in the base of shrubs; they’re easy to spot. In areas where it’s not practical to dig out the roots of these weed trees, I’d treat the stump with glyphosate promptly after cutting to kill the root system. An alternative to using an herbicide is to keep cutting back the weed trees as they resprout.

Out, dead wood, out

Also, I recommend pruning dead wood out of trees and shrubs as needed. Most trees and shrubs are fully leafed out by now, so it’ll be easy to figure out what plants or sections of plants have extensive winter damage and need to be removed. For plants that are slowly leafing out, I’d wait and see if you’re unsure whether to prune it or remove it.

Pest management

To manage pests and diseases, consider using integrated pest management to help, rather than relying on pesticides. You can start by choosing the proper plant for your site and using good planting practices, such as amending the soil with compost and planting it at the proper depth.

When possible, select plants that are resistant to common diseases and give them the appropriate care to minimize problems. Monitor all plants carefully for insects and diseases. If trouble arises, identify the problem, and use the least toxic control measure when damage is not tolerable. Timing is also important — apply controls when pests and disease are the most susceptible.

Keep in mind that you shouldn’t start spraying just because you see insects; some of them might be beneficial to the environment or harmless. When you use an insecticide, you kill the good insects, along with the bad ones. Look for more pest- and disease-resistant plants to replace any plants that have had a pattern of problems in your garden.

When reviewing proposals for chemical treatments, ask questions about the target pests and timing. Make sure you really need the application and consider the harmful effects on the environment. Organic pest controls aren’t necessarily safe for you or your pets, so be sure you understand the products before using them in your garden.

Magnolia scale can kill a magnolia if not controlled — if you treated for magnolia scale last year (dormant oil treatments are very effective), then you should not need to repeat the treatments this year. Monitor the tree and treat when there are scale insects present.

• Tim Johnson is director of horticulture at Chicago Botanic Garden,

Article Comments
Guidelines: Keep it civil and on topic; no profanity, vulgarity, slurs or personal attacks. People who harass others or joke about tragedies will be blocked. If a comment violates these standards or our terms of service, click the "flag" link in the lower-right corner of the comment box. To find our more, read our FAQ.