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Gardening in Washington State

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Yellowjackets! Ouch!

Yellowjackets and paper wasps may become aroused and attack in defense of their nest when disturbed and can be pests when they build a nest on or near your house.  Nests of most species are placed underground in rodent burrows or other soil cavities and colonies attain maximum size in August and September. Worker yellowjackets, then at their peak, become pestiferous.


Common yellowjackets from trap
Photo by Dave Pehling, WSU Extension, Snohomish County

Yellowjackets may be attracted in large numbers to food at picnics, to honey bee colonies, and to garbage cans.

For additional information about yellowjacket wasps and paper wasps, see the WSU publication “Yellowjackets and Paperwasps” and “Managing yellowjackets” from WSU Pestsense,

Submitted by: Dave Pehling, Octobr 23, 2017.


Sick looking Cedars?

Have you noticed the western red cedars in your neighborhood showing lots of brown fronds lately?  In most cases, these trees are not really suffering from some horrible tree disease or pest but simply shedding their old foliage.  This annual phenomenon is called “cedar flagging” and is much more noticeable this fall due to our prolonged summer drought.

Cedar flagging. Photo by Dave Pehling.

Most of the dead “flags” will be blown off with our first good wind storm and the trees will look as healthy as ever.

For information on cedar flagging, see WSU Hortsense at

Submitted by: Dave Pehling, October 16, 2017


A mole lotta love

Our common Pacific and Townsend’s moles put aside their solitary ways at this time of year – and begin thinking about love.

Have you noticed a surge in mole hills in your yard? Male moles expand their tunnels to look for “girl friends”.  Particularly ambitious males could make as many as 302 mole hills in just 77 days!

Since passage of an anti-trapping bill in 2000, legally managing moles in home yards and gardens has become very difficult. However, you can read about your legal options in the WSU Fact Sheet, “Mole Management in Washington Backyards”.

Submitted by: Dave Pehling, February 14, 2017


Space Availability and Plant Selection for a New Hedge

It is important to plan the layout of a screen or hedge before installation. Once trees or shrubs are planted and begin growing, it can be difficult to make changes. Factors to consider include the available space on the property; whether it will be a formal or informal design; the need for deciduous or evergreen plants; the aesthetics of plant texture; and, in areas prone to wildfire, the need for defensible space. One of the biggest design mistakes made is planting species that are too large for the designated area.

Photo credit: Charles Brun, WSU Horticulture Specialist, emeritus

Photo credit: Charles Brun, WSU Horticulture Specialist, emeritus

The WSU publication Selecting Plants for Screens and Hedges EM089E  can help with the many questions regarding planning, design and plant selection of a new hedge

Submitted by: Paula Dinius, May 11, 2016


I didn’t get my spring bulbs planted yet. Is it too late?

Ideally, spring bulbs need to be planted in early November or before the first hard frost in your area. However, bulbs are also very forgiving and may still bloom even when put into the ground as late as early March.


Wikimedia commons, “2015-04-27 Tulip,White and Red in Sasayama, Hyogo Japan

Bulbs grow and bloom the best when planted in an area that receives direct sunlight and adequate moisture. They can be planted in groupings (3 or more) or in a straight line depending on available space in your planting location. It is a good idea to think about the height of the bulbs, not just the color, if you are planting several different types in the same area in order to create a pleasing display.

For more information, see the WSU publication PNW164 “Propagation of Plants from Specialized Structures.”

Submitted by: Sheila Gray, March 7, 2016


Horticultural Oils

It is fairly easy to accidentally damage your plants or nearby environments when applying horticultural oils. Here are some important points to consider before using these oils:

juniper_PetiteHorticultural oils are non-specific so if beneficial insects get sprayed, they will die along with the insect pest.

Only spray plants with confirmed pest problems in order to conserve the beneficial insects in your garden and landscape.

Be aware that junipers and spruce often lose their blue color when oil is applied.

Oil and water do not mix: horticultural oil will inhibit oxygen transfer, which can kill fish. Keep applications and their airborne oil drift out of waterways.


For information on how to use horticultural oils successfully, see the WSU Extension fact sheet Pesticide Ingredient: Horticultural Oil.

Submitted by: Catherine Daniels, Jan. 7 2016


Do cedar mulches kill other plants?

Many living, growing woody plants contain allelopathic chemicals, which can prevent seeds from germinating or kill young seedlings. Most compounds have no effect upon established plants. Cedars (Thuja spp.) have not been found to have this ability. Even Juglans nigra (black walnut), the best known allelopathic species, has not been shown to have negative effects when wood chips are used as a mulch.

Wood chip mulches are beneficial to established plants.

Wood chip mulches are beneficial to established plants.

For more information on wood chip mulches, see “Using Arborist Wood Chips As a Landscape Mulch” WSU Extension Fact Sheet FS160E.

Submitted by: Linda Chalker-Scott, November 2, 2015


Fall Garden Tips: Time to Plant Garlic

In the Northwest, garlic is planted as cloves in the fall. Garlic requires full sun (at least 6 hours per day). It is best started by direct sowing seed garlic that can be purchased through some garden centers, catalogs, and online websites. Certified seed garlic has been grown specifically for planting in the garden and is free of insects and diseases.

Plant garlic in early to mid-fall (September to October) in eastern Washington gardens and late fall (November) in western Washington gardens. To prepare the planting area, loosen the soil to improve drainage.


Plant large cloves that are clean and dry and plant them the same day the bulb is broken apart. Cloves showing any discoloration, stippling, or bruising should be discarded. Plant the cloves so that the tops are 2 inches below the soil line, and place the garlic clove flat-side down and pointed-side up in the hole. Garlic should be planted 4–6 inches apart in rows that are spaced 12–24 inches apart.

For more information on growing garlic, see Growing Garlic in Home Gardens.

Submitted by: Nicole Martini, October 26, 2015


Harvesting Winter Squash

Winter squashes are harvested fully mature when the skins feel hard and waxy. In autumn, there is no hurry to harvest winter squashes unless excessively cold or wet weather is approaching. Pick winter squashes with stems attached. Cure in a warm, dry place and store at room temperature. Under these conditions, winter squashes store between 3 to 5 months. After the final harvest, be sure to remove and destroy the leftover plant debris. Alternatively, turning under the remaining plant material into the garden soil can help replenish nutrients and contribute to the organic content of the soil.

Photo credit: Trevor Mattea, Wikimedia Commons

Photo credit: Trevor Mattea, Wikimedia Commons


For more information please see WSU publication Growing Squash in Home Gardens FS087E

Submitted by: Catherine Daniels, Oct. 21, 2015


Will woody mulch acidify my soils?

In field situations it is difficult to significantly alter soil pH without the addition of chemicals. Temporary changes in pH may be found in the decomposing mulch layer itself, but these have little effect on underlying soils. Significant changes in soil pH can only occur after decades or centuries of mulch use.

pine needles

For more information on wood chip mulches, see “Using Arborist Wood Chips As a Landscape Mulch” WSU Extension Fact Sheet FS160E .

Submitted by: Linda Chalker-Scott, October 12, 2015


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