Fall garden Q&A: Keeping out pests, pruning trees and lots of lawn care advice

Washington Post Gardening columnist Adrian Higgins answered questions recently in an online chat. Here is an edited excerpt.

Q: What can the home gardener do about clover taking over a lawn? Last year, I fought crabgrass, and this year, it’s clover. Crabgrass was easier to pick out by hand. Any easier, earth-friendly remedies?

A: Clover isn’t so much a weed as a state of mind. If you come to regard it as a desirable component of the lawn, you won’t have to keep fighting it. Yes, there are herbicides that work against it, but it actually feeds nitrogen into the soil, is an important nectar source for pollinators and only gets expansive when the lawn is allowed to thin. Live with it, but push it back by overseeding the lawn.

Q: What is the best time to prune trees (suckers from plum trees and extraneous branches from a Japanese maple in a pot)? And must the cuts be treated with anything after pruning?

A: Most pruning of deciduous plants is best done during winter dormancy, not least because you can see the structure of the tree or shrub much better then. Other good times to prune are after the flush of spring growth and also right after flowering, so that you don’t affect bud set for the following season. One of the worst times for pruning is over the next few weeks, when cutting back could induce fresh new growth that will be susceptible to frost damage. Wound treatments are no longer recommended.

Q: I have about 40 Knock Out roses. Some have branches that look stressed: lighter green leaves and rust-colored spots. What can I do to address this? And on a related note, would this be a good time to fertilize the roses?

A: I have reached a point where I can’t look at another Knock Out rose. If you enjoy this overplanted magenta flowering shrub, more power to you. You might lay a modest top dressing of rose feed to keep its floral cycles going through the fall. This variety is prone to rose rosette disease, spread by mites. Remove infected plants to curtail its spread.

Q: This August, crabgrass has taken over my lawn. What steps can I take now to minimize the problem next year?

A: Crabgrass is a direct result of lawns that are too thin. Thick, lush lawns are your best bet against weed infiltration. Crabgrass is an annual, so you can either spot-treat or simply hoe them now, but you will have to renovate the lawn to address the problem. Count on using a pre-emergent herbicide in early spring with follow-up applications.

Q: I have a 25-by-25-foot community garden plot that I have divided into quarters, and I rotate my beds each year for a four-year rotation. But for a garden that small, is rotation actually beneficial?

A: Rotation is desirable but almost impossible in such a small garden. I would move varieties around as best you can, but if you see

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Garden Mastery: Here’s how to identify and manage insect pests in your garden

Summer is the “time of the garden,” when flowers are riotously blooming and fruit and vegetables are ripening. However, you may find you’re not the only one enjoying the fruits of your labors.

In order to support their next generation, many nonvertebrate pests, such as aphids and snails, may be eating leaves, dining on fruit, and sucking juices out of your plants.

How can you manage these pests? First, you must ask yourself: How much are you willing to share your garden with wildlife?

While there is no wrong or right answer to this question, all gardeners need to draw a line at the amount of damage they are willing to endure. A garden is an ecosystem of plants and animals, with many interdependent parts. Eliminating one or more elements can affect the entire system.

Begin by identifying what is damaging your plants. While birds and other animals may be the cause, in this article we’ll focus on insect pests. This can be a challenge, given the hundreds of insect species in San Diego. Many insects are beneficial to your garden, as they pollinate your plants, eat or parasitize harmful insects, and add to the overall enjoyment of your efforts. But other insects are destructive, such as the tomato hornworm — just one can destroy an entire tomato plant very quickly.

There are many resources to help you identify what is damaging your plant. If you can actually see the culprit on its damaged host plant, you can ask other gardeners’ advice, visit local certified nurseries (bring a sample in a closed plastic bag), or contact the San Diego Master Gardeners’ Hotline (858) 822-6910 from 9 a.m. to 3 p.m. weekdays for assistance.

You can also check the University of California Integrated Pest Management (IPM) website Pest Notes or the Plant Problem Diagnostic tool (both found at http://ipm.ucanr.edu/PMG/menu.homegarden.html). If you can see the damage but not the perpetrator, you can research via garden books, and at the University of California Integrated Pest Management (IPM) website.

The eggs on these fiber stocks are Green Lacewing eggs. The larvae stage prey upon a large number of insect pests.

Friend or foe? The eggs on the fiber stocks are Green Lacewing eggs. The larvae stage of this insect prey upon a large number of insect pests, making them beneficial in your garden.

(Regents of the University of California)

After identification, your next step is to understand the life cycle of the pest and then weigh the benefits of controlling now against the benefits at a later life stage. For example, the aforementioned and dreaded tomato hornworm metamorphizes into the large sphinx moth, a nighttime pollinator important to pitahaya and other night-blooming plants. And many caterpillars are only present for a month or so before they become beautiful butterflies, so eliminating them after you have already picked most of your crop might not be worth your time and effort.

Like its name suggests, the IPM system uses an integrated method for managing pests of all types. Once you have chosen your source for pest management, monitor the effectiveness of the methods used.

Prevention is always

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Attracting Natural Insect Predators to Control Garden Pests

In the world of animals, there are carnivores (predators) and herbivores. The carnivores are meat eating, and feed on the herbivores. The same happens in the insect world, and we can use this strategy to naturally control pests in our vegetable gardens. Insect predators eat other insects.

What are Beneficial Insect Predators?

Examples of beneficial insect predators that feed on crop pests include ladybugs, lacewing bugs, spiders, wasps, certain mites, damsel bugs and many others. There are ways of attracting these insect predators to our gardens.

One of these is to create an insectary by using a diverse range of predator attracting plants.The garden insectary is a type of “companion planting”. By planting a wide range of plants you can provide alternative food sources (such as nectar and pollen, required by many predators as part of their diet) as well as habitat and shelter. For example, you can control aphids by attracting an aphid-specific predator such as Aphidius by planting lupins or sunflowers. Your insectary only needs to be big enough to hold six to seven varieties of plants that attract insects. Once these plants have matured, your beneficial insects will efficiently take over the insect pest control in your vegetable and fruit garden for you.

Tips for Setting up Your Insectary

  1. Members of the carrot family (wild carrot, dill, coriander, fennel and angelica) are all excellent insectary plants. They all produce tiny flowers which are required by parasitoid wasps. Large nectar-filled flowers can drown these tiny parasitoid wasps.
  2. Grow plants of various heights in your insectary: lace wings lay their eggs in protected, shady areas. Ground beetles like the cover from low growing plants such as mint, thyme or rosemary
  3. Flowers such as daisies and mint-like plants such as peppermint, spearmint etc will attract robber flies, hover flies and predatory wasps.
  4. Plant insectary annuals between your vegetable beds. This will lure beneficial insects as well as adding a touch of decoration to your garden.
  5. Let some of your vegetables grow to flower (carrots, broccoli, brussel sprouts, cabbage, bok choy etc).

Other Great Insectary Plants

Good insectary plants not already mentioned include the following:

  • Alyssum
  • Amaranthus
  • Convolvulus
  • Cosmos
  • Daucus carota (Queen Anne’s Lace)
  • Digitalis
  • Limonium (Statice)
  • Lemon balm
  • Parsley
  • Peonies
  • Verbascum thaspus

A garden insectary should be a permanent component of all gardens. The longer your insectary is in place, the more effective it will be as insects get to know a place that provides food, shelter and above all, a source of nearby food. Results are cumulative. As your plantings mature and resident populations of beneficial insects are established, the need for toxic chemical pesticides will diminish. Your garden will become a more natural and balanced environment for the production of healthy vegetables and flowers.…

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