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Landscaping News and Information

March 15, 2017

Emerald Ash Borer (EAB), detected in Boulder, CO, in September 2013, is a nonnative insect with no natural enemies to keep it in check. EAB attacks only ash trees, and the pest is responsible for the death and decline of tens of millions of ash trees in the United States. Colorado has many ash in the urban forest (it’s estimated about 15% of urban trees are ash). Ash trees are popular in Colorado with an estimated 98,000 in the city of Boulder alone; the Denver Metro area has an estimated 1.45 million ash trees. As of early 2014, the only confirmed EAB infestations in Colorado are in Boulder County.

The emerald ash borer is a small, green metallic beetle first detected in North America in 2002 in southeastern Michigan. The adult beetle is approximately one-half inch long with a metallic green head and back; the abdomen is coppery-purple in color. The larvae are up to one-half inch long, have prominent bell-shaped segments and are creamy-white in color.

The emerald ash borer attacks only ash trees, and all ash species – including green, white, black and blue – are at risk. It is possible that EAB could infest an ash tree for three or four years before signs of tree decline are visible. Infestation signs include:

Sparse leaves or branches in the upper part of the tree with D-shaped exit holes about 1/8 inch wide

New sprouts on the lower trunk or lower branches

Vertical splits in the bark

Winding S-shaped tunnels under the bark

Increased woodpecker activity

Note that drought and general urban stress of Colorado’s ash trees may mimic EAB symptoms. However, if an ash tree is experiencing die-back or looking unhealthy, residents are encouraged to have it examined by a professional tree company and contact the Colorado Department of Agriculture or their city or county forestry office.

Since November 2013, a quarantine has been in effect in Boulder County, the town of Erie, and three other small parcels of land adjacent to Boulder County in Colorado. The quarantine prohibits any ash products (including logs and green lumber, nursery stock, scion wood and bud wood, chips and mulch, stumps, roots and branches) and all hardwood firewood from leaving the quarantined area. Movement of ash products within the quarantine area is permitted.


Many gardeners like to think that all they need to do is put a perennial in the ground and forget about it. Alas, even such Methusalahs of the garden as peonies, which can go a human lifetime without needing to be cut back, can be swamped by neighboring plants or decline over time. Other perennials, such as columbine or non-Oriental poppy varieties, are really glorified biennials. If they last more than two years, consider yourself lucky.

Removing spent flowers and cutting back foliage is the only routine maintenance most perennials require. For example, cutting faded flowers dramatically prolongs the flowering season of daisies and salvias. Removing spent flowers is usually a matter of personal taste. Some people like their gardens to appear crisp and immaculate.

Many gardeners enjoy the beauty of seedheads and wait until plants begin to look tatty and unattractive before severely cutting them back. When cutting back plants, take care not to remove basal rosettes or growing points, because it may weaken or even kill plants.

Colorado winters can enhance the subtle beauty of a border if you leave stems and stalks in place until early spring before cutting them to the ground. A thorough cutback in February or March, with a good top dressing of compost or mellowed manure, is all most standard perennials need to add years of beauty to your garden.

Don’t hesitate to move plants that aren’t performing well where you originally planted them. A more appropriate site can do wonders for plants that aren’t performing up to your expectations.

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