WSU Extension Snohomish County Master Gardeners
SCMG Education Outreach
September GARDEN TIPS AND TASKS
SCMG Education Outreach
September GARDEN TIPS AND TASKS
SPOTLIGHTS IN THIS ISSUE
PEST MONITORING AND MANAGEMENT - Slugs, juniper twig blight, English ivy, protecting beneficial insects.
GENERAL OVERALL MAINTENANCE - Watering, drought, assessing plants, lighting.
EDIBLES - Powdery mildew, extending growing season, cover crops, garlic, harvesting late summer crops.
FLOWERS AND FOLIAGE - Staking, mulching, conifer flagging, hedges, dividing, propagating, planting spring bulbs.
LAWNS - Creating new lawns, rehabilitating existing lawns.
PLANT OF THE MONTH - Rudbeckia hirta, Black-eyed Susan/Gloriosa Daisy.
PEST MONITORING AND MANAGEMENT - Slugs, juniper twig blight, English ivy, protecting beneficial insects.
GENERAL OVERALL MAINTENANCE - Watering, drought, assessing plants, lighting.
EDIBLES - Powdery mildew, extending growing season, cover crops, garlic, harvesting late summer crops.
FLOWERS AND FOLIAGE - Staking, mulching, conifer flagging, hedges, dividing, propagating, planting spring bulbs.
LAWNS - Creating new lawns, rehabilitating existing lawns.
PLANT OF THE MONTH - Rudbeckia hirta, Black-eyed Susan/Gloriosa Daisy.
PEST MONITORING AND MANAGEMENT

Slugs
Watch for…
Watch for…
- Plants with shredded leaves or nearby slime trails.
- Western Washington is an ideal environment most of the year for slugs as it usually provides a wet climate that creates the moisture slugs need to survive and lots of plants to eat.
- Washington State University (WSU) Snohomish County Extension publication; Community Horticulture Fact Sheet # 92 Slugs.
- Western Washington is an ideal environment most of the year for slugs as it usually provides a wet climate that creates the moisture slugs need to survive and lots of plants to eat.
- Keep a sharp eye out for slug eggs. Destroy.
- For information on damage, slug control, and eggs, see:
- WSU Snohomish County Master Gardener Foundation publication; Tips and Tasks; March and August.
- For information on damage, slug control, and eggs, see:
- Bait, trap, or hand pick adults and destroy.
- Replenish slug bait during rainy periods or set it out under cover or in a trap to keep it dry.
- Be aware that some baits are toxic to humans and pets.
- Pacific Northwest (PNW) Insect Management Handbook; Slug Control.
- WSU website; Hortsense; Common Insects & Mites: Slugs.
- Be aware that some baits are toxic to humans and pets.
- Photo credit: Slug damage on iris; A.L. Antonelli; WSU.

Juniper twig blight
Watch for…
Watch for…
- Yellow to red, or dead foliage on branches.
- New growth is highly susceptible to the fungal growth that causes juniper twig blight.
- Carefully prune out and destroy affected twigs and branches.
- Pruning to shape should occur between February and April only.
- Grow resistant plants and space them for good air circulation.
- Avoid overhead watering, or water when plants will have time to quickly dry.
- Avoid over fertilizing.
- PNW Plant Disease Management Handbook publication; Juniper (Juniperus spp.) -Twig Blight.
- WSU Snohomish County Extension publication; Juniper Troubles.
- Photo credit: Phomopsis twig blight on juniper; R.S. Byther, WSU

English ivy
Once a desired groundcover, English ivy readily grows outside its bounds and is categorized as a noxious weed in Washington. It is a threat to native forest land. If allowed to climb trees, its weight can cause trees to topple in high winds. After heavy rains, slopes may fall away from beneath the ivy because it is a poor soil stabilizer.
If you still desire to have a controlled patch in your yard, now is a good time to establish your dominance!
Once a desired groundcover, English ivy readily grows outside its bounds and is categorized as a noxious weed in Washington. It is a threat to native forest land. If allowed to climb trees, its weight can cause trees to topple in high winds. After heavy rains, slopes may fall away from beneath the ivy because it is a poor soil stabilizer.
- WSU publication; The Hazards of English Ivy.
- Unwanted seedlings, ivy starting to climb or form seeds.
- Remove unwanted seedlings, root and all.
- Cut ivy stems at ground level and remove as much of the vertical growth as possible. Portions too high to reach will wither and die.
If you still desire to have a controlled patch in your yard, now is a good time to establish your dominance!
- Keep edges of garden ivy trimmed and contained.
- Cut off flower heads to avoid seed spread.
- Do not allow it to climb trees!
- WSU website; Hortsense; Weeds: English ivy: Hedera helix.
- Pfeiffer, Christina and Mary Robson, Month-by-Month Gardening Pacific Northwest, Cool Springs Press, 2017.
- Photo credit: English ivy vines climbing trees; B.M. Johnson; WSU.
- Learn to appreciate this mistakenly feared garden ally. As we move into fall, we encounter more spider webs. We also see more spiders, as males are out looking for potential mates.
- Spiders are beneficial predators and often the most important biological control of pests in and around the home and garden.
- WSU Extension publication; Beneficial Insects, Spiders, and Other Mini-Creatures in Your Garden: Who They Are and How to Get Them to Stay.
- WSU Extension publication; Spiders.
- Learn which spiders may be harmful to humans and where they are found. Western Washington is not home to any dangerous spiders.
- Washington State Department of Health publication; Spiders.
- Spiders are beneficial predators and often the most important biological control of pests in and around the home and garden.
- Accurately identify the pest or problem. For help you can contact the Master Gardener hotline at 425-357-6010 or send an e-mail and photo to: snocomg@gmail.com.
- The Snohomish County WSU Master Gardener Office Clinic is open from 10:00 AM to 4:00 PM Monday through Thursday. The clinic is located in the administration building at Willis D. Tucker Park, 6705 Puget Park Drive, Snohomish, WA 98296.
- To find other In-Person Plant Problem Clinic sites, use the link below.
- If you want to do the research on your own, here’s a helpful website:
- Thoroughly read pesticide labels to ensure safe handling. Choose the least-toxic options, and use them judiciously. Instead of pesticides/herbicides, consider cultural changes as well as physical or biological controls. Use chemical controls only when necessary.
- The label must state that the pesticide is for the problem you are addressing.
- Grow Smart Grow Safe website.
- The label must state that the pesticide is for the problem you are addressing.
- Be sure to take any unused pesticides to your local Household Hazardous Waste center for safe disposal.
- Washington State Department of Ecology website; Household Hazardous Waste & Moderate Risk Waste.

GENERAL OVERALL MAINTENANCE
Enjoy the warm and sun, the bounty,
and bug/slug squishing chores,
because soon enough will be gray days
chasing you back indoors!
Coping with Drought
Irrigation is a choice between saving on your water bill vs. saving your valuable plants.
For detailed advice, see below:
Consider enhancing the garden for evening strolls.
Enjoy the warm and sun, the bounty,
and bug/slug squishing chores,
because soon enough will be gray days
chasing you back indoors!
Coping with Drought
Irrigation is a choice between saving on your water bill vs. saving your valuable plants.
For detailed advice, see below:
- Washington State University (WSU) Extension publication; Drought Advisory: Water Conservation in Gardens and Landscapes.
- WSU Island County Extension publication; Xeriscaping: planning and executing a waterwise landscape.
- Increased insect and other wildlife damage. During droughts, these creatures will use your plants for their needs.
- Spider mite webs. Mites may hide on dust-covered leaves.
- Undersized and off-flavored fruit and vegetables.
- Branch dieback, diminished hardiness, increased disease susceptibility, root death, or plant death. All of these are long-term results of drought.
- Spray water to remove accumulated dust from foliage.
- Avoid adding fertilizers and pesticides which can burn plants.
- Keep turf 2 feet from tree trunks and add mulch if not already present. Removing ground covers from tree bases will reduce competition for water.
- Shade plants where possible to reduce evaporation. Floating row covers, latticed pergolas, or canopies may lower temperatures and reduce desiccation.
- For more information on row covers see the edibles section:
- WSU Snohomish County Master Gardener Foundation publication; Tips and Tasks; June.
- For more information on row covers see the edibles section:
- Avoid watering plants, especially annuals, that have passed their prime or are diseased. Remove them instead.
- Water deeply, but less frequently, as trees, shrubs, and perennials prepare for the colder months ahead.
- WSU Extension publication; Drought Tolerant Landscaping for Washington State EM087E(1).pdf
- WSU Extension publication; Washington’s Water; Drought, Conservation, and Irrigation.
- Add mulch where needed. It can reduce evaporation by as much as 50%.
- Do not use rocks, peat moss, or plastic. (Rocks can absorb, store, and radiate heat.) See:
- WSU Extension publication; Drought Advisory Water Conservation in Gardens and Landscapes EM4834.
- Do not use rocks, peat moss, or plastic. (Rocks can absorb, store, and radiate heat.) See:
- Assessing the garden
- Consider which chronically stressed plants to move when fall becomes cooler and the rains are more regular.
- Group plants according to their light and water needs. Hydrozoning will reduce water usage.
- WSU Island County Shore Stewards News; Xeriscaping: planning and executing a waterwise landscape.
- Tag, map or photograph the plants that had plant disease or insect attack and plan to remove their mulch and dropped leaves at autumn’s end. Add new mulch to those areas. Overwintering disease spores and insects are down there waiting to re-attack!
- Research your plant ailments for how and when to treat. For help, consult Master Gardener Office clinicians. For contact information, see the Pest Monitoring and Management section above.
Consider enhancing the garden for evening strolls.
- Safe landscape lighting (12 volt, LED, or solar) is a great way to illuminate your garden.
- Path lights add safety; up-lighting a shrub or an interesting tree trunk makes a beautiful statement. If you have a pond, shine a light on the water.
- However, too much light disturbs the sleep and migratory patterns of insects and birds.
- University of California Los Angeles (UCLA) Institute of the Environment & Sustainability publication; Study reveals which outdoor lighting minimizes harm to insects.
- U.S. Fish and Wildlife Service publication; Dim the Lights for Birds at Night!
- However, too much light disturbs the sleep and migratory patterns of insects and birds.
- Plants for night gardens:
- Night-scented flowers such as nicotiana, jasmine, evening-scented phlox (Zaluzianskya ovata), petunias, or angel’s trumpet (Brugmansia) will captivate your senses. These and others may still be available at local nurseries.
- For nightly glow, add white-flowered plants like hydrangea or silver-leaved plants such as Senecio that reflect moonlight.
- Photo Credit: Nicotiana and white jasmine; Sheryl Kelly; WSU Snohomish County Master Gardener.

EDIBLES
Maintenance / Clean-up
Maintenance / Clean-up
- Rain and damp weather in the fall may bring on diseases like powdery mildew. Such problems can often be tolerated until the end of the season. If the problem is overwhelming, simply pull out and destroy affected plants.
- Washington State University (WSU) Clark County Master Gardener publication; Garden Mastery Tips; Powdery Mildew.
- Clean-up now can prevent disease and pests from overwintering in your garden.
- Keep weeds from going to seed. It will save you time and effort next year.
- Many plants in the garden are ready to go into the compost bin after they are through producing.
- Do not put weed seeds into your compost.
- It’s ok to put them into commercial yard waste containers since it is heated enough to kill weed seeds
- Do not compost diseased plants.
- For a complete guide to composting, see:
- WSU publication; Backyard Composting.
- Swelling or galls near the base of raspberry canes may indicate crown borers are present. Remove infected canes and crowns and destroy.
- Pacific Northwest Pest Management Handbooks publication; Blackberry and Raspberry-Raspberry crown borer.
- WSU website; Hortsense; Raspberry: Raspberry crown borer.
- Photo credit: Raspberry crown borer larvae and damage; E.P. Breakey.
- September is a good month to assess what was successful and what was not. Keep notes for next year.
- If you have a greenhouse, hoop house, or just a raised bed with row cover, you may be able to extend your growing season past this month.
- WSU Snohomish County Extension publication; Plastic Culture to Extend Growing Season.
- If you haven’t ordered your garlic for October/November planting, check nurseries and catalogs for flavor descriptions and varieties successful in Washington. Garlic in grocery stores has often been treated not to sprout.
- WSU Extension publication: Vegetables: Growing Garlic in Home Gardens.
- WSU publication: The Joys of Garlic.
- If you have bare soil in your garden, you can plant a cover crop.
- It serves as a living mulch while growing.
- Legumes, like fava beans, crimson clover, hairy vetch, and peas fix nitrogen in the soil.
- Grasses and cereals, like annual ryegrass and barley, when tilled under also improve your soil.
- WSU Extension publication; Cover Crops for Home Gardens West of the Cascades.

Cover crops
- If you have bare soil in your garden, you can plant a cover crop.
- It serves as a living mulch while growing.
- Legumes, like fava beans, crimson clover, hairy vetch, and peas fix nitrogen in the soil.
- Grasses and cereals, like annual ryegrass and barley, when tilled under also improve your soil.
- WSU Extension publication; Cover Crops for Home Gardens West of the Cascades.
- https://s3.wp.wsu.edu/uploads/sites/2079/2015/06/Cover-Crops-for-Home-Gardens-West-of-the-Cascades-WSU.pdf
- Corn can be harvested when the silks turn brown and kernels are milky.
- Harvest potatoes when the tops die down. Store them in a dark location.
- Pick green tomatoes and ripen them indoors if frost or blight threatens.
- To avoid late blight, protect from rain and dew.
- WSU website; Hortsense; Tomato: Late blight.
- To avoid late blight, protect from rain and dew.
- Photo credit: Protection for tomatoes from rain and dew; Vicki Sorg; WSU Snohomish County Master Gardener
- Leave winter squash and pumpkins in the field to ripen.
- Harvest when they are fully mature and the skin is hard and waxy. Cut the stem a few inches away from the fruit to protect the area where it joins the squash.
- Do not leave them in the field if weather remains wet. These conditions encourage rot and mildew.
- Harvest dry beans, such as black beans or cranberry beans, which are grown to dry and store for later use.
- If the garden stays mostly dry, allow beans to hang on the vines until the pods are dry and open easily, then gather.
- Lay them in a single layer on porous material, such as cardboard or a screen, in a well ventilated area to finish drying.
- If the garden is wet before the beans are ready, mold can be a problem.
- Protecting the plants with a plastic ”roof” may prevent mold.
- Harvest the beans after the pods have stopped growing and are plump (and hopefully have started to dry).
- Lay these beans in a well ventilated area to finish drying.
- Dry beans can be left in the pods for weeks or months before shelling. If the beans are shelled before the pods dry, they will need extra drying time to store without mold or rotting.
- Get complete information on growing and harvesting dry beans at:
- WSU Extension publication; Vegetables: Growing Dry Beans in Home Gardens.
- Get complete information on growing and harvesting dry beans at:
- If the garden stays mostly dry, allow beans to hang on the vines until the pods are dry and open easily, then gather.
- Some late summer vegetables can be left in the garden to mature slowly as the weather cools. Watch crops like late cabbage to see that they remain healthy-looking and cut them while the heads are still solid.
- Pears should be harvested before they are mature.
- WSU publication; Western Washington Tree Fruit & Alternative Fruits.
- The best general source for vegetable gardening in Western Washington is:
- WSU Extension publication; Home Vegetable Gardening in Washington.
- If you have a super-abundance of any edibles, remember your local food bank. Check to see when they accept donations.
FLOWERS AND FOLIAGE
Maintenance/Clean-Up
This a good time to install new trees and shrubs.
- Stake tall flowers to keep them upright during autumn winds.
- Dig, clean, and store tuberous plants such as begonias if frost threatens.
- Oregon State University Extension publication; September Garden Calendar.
- Continue deadheading most plants to extend their flowering season. However, avoid deadheading roses in late summer, which could encourage growth that’s vulnerable to winter damage.
- Washington State University (WSU) Extension publication; Growing Roses in Washington, FS164E.
- If you cut back the spring blossoming perennials to get a second bloom, that second bloom may be spent. It’s time to cut back or shear them again. This time, shape the plant at the size and configuration you desire.
- On woody perennials, do not cut into the wood section when shaping.
- Lavender can be cut back to a few leaf clusters above the woody stems, but no farther. Shape as desired. If this is not done every year, the plant flops open.
- On woody perennials, do not cut into the wood section when shaping.
- Mulch: Resist the impulse to rake up all fallen leaves, twigs, and other plant debris from garden beds. This natural mulch provides a habitat for beneficial insects and fungi, and recycles organic matter back into the soil.
- However, if the plant had insect or disease issues this year, remove the fallen debris and mulch and replace with fresh mulch. You don’t want to assist overwintering spores or insects.
- Pfeiffer, Christina and Mary Robson, Month-By-Month Gardening in the Pacific Northwest, Cool Springs Press, 2017.
- Recycle disease-free plant material into compost.
- WSU Extension publication; Backyard Composting, EB1784E.
- However, if the plant had insect or disease issues this year, remove the fallen debris and mulch and replace with fresh mulch. You don’t want to assist overwintering spores or insects.
- Conifer flagging: Don’t despair if you see some discoloration and loss of foliage in certain conifers, particularly western redcedar and some pines. This is a natural process called “flagging,” where the tree is prioritizing its resources. This is a normal part of conifer growth.
- WSU Extension publication; Seasonal Foliage Discoloration and Loss in Pacific Northwest Evergreen Conifer Trees.
This a good time to install new trees and shrubs.
- For information on how to plant, stake, fertilize, and water newly planted trees and shrubs, see:
- WSU Extension publication; Planting Trees and Shrubs in the Landscape, FS07E.
- If your garden lacks privacy, consider adding a living screen or hedge to your landscape. A living screen will block an unsightly view, reduce noise and dust, provide a buffer against the wind, and give shelter to wildlife.
- How far apart should you space hedge plants? How tall should they be? Evergreen or deciduous? The following publication will answer your questions and give you a multitude of options.
- WSU Extension publication; Selecting Plants for Screens and Hedges, EM089E.
- How far apart should you space hedge plants? How tall should they be? Evergreen or deciduous? The following publication will answer your questions and give you a multitude of options.
- It’s also a good time to refresh those tired containers.
- Add colorful fall accents, such as violas, mums, asters, kale, and purple fountain grass.
- Consider planting a small evergreen tree or shrub surrounded with winter favorites such as pansies, sedums, or heathers.
- Divide spring-blooming perennials, such as daylilies, hardy geraniums, salvias (not woody), garden phlox, iris, peonies, bleeding heart, and Veronica.
- WSU Spokane County Extension publication; Dividing Perennials.
- When to divide various plants and how to propagate them to fill your empty spaces? See:
- WSU Spokane County Extension publication, Propagating Perennials.
- It’s the start of spring bulb planting time! Snowdrops, crocus, daffodils, tulips, hyacinth, etc. will reward you with fabulous color from late winter through the end of spring.
- Choose firm, plump bulbs free of disease and decay.
- Plant as soon as possible after purchase; or store bulbs in mesh or paper bags in a dark, dry place until ready to plant.
- Generally, plant to a depth of two to three times the height of the bulb.
- Bulbs have their own energy stores; there’s no need to fertilize when initially planted.
- Plant in well-draining soil in the garden or in pots. Bulbs can be staggered in layers in the soil, so they will blend together when emerging. For example, plant large bulbs such as hyacinth deeper, with daffodils above, and crocus above those.
- After placing bulbs, cover with soil and top with mulch. Water well if rain is not imminent.
- To protect your bulbs from squirrels and voles check out the link below.
- University of New Hampshire Extension publication; How Can I Keep Wildlife from Eating My New Bulbs?
- For simplified information on bulb planting, see:
- University of Minnesota Extension publication; Planting Bulbs, Tubers, and Rhizomes.
LAWNS
Maintenance/Clean-up/Planting
Now that temperatures are cooler and rain may be on the way, it could be time to reseed an existing lawn or even start a new one. It’s still warm enough for seeds to start growing before cool weather slows everything down, and the coming rains mean that you won’t have to worry so much about keeping up with watering.
Maintenance/Clean-up/Planting
Now that temperatures are cooler and rain may be on the way, it could be time to reseed an existing lawn or even start a new one. It’s still warm enough for seeds to start growing before cool weather slows everything down, and the coming rains mean that you won’t have to worry so much about keeping up with watering.
- Creating a new lawn:
- Prepare a new seedbed by tilling in 2-3 inches of compost before fertilizing, seeding, and watering.
- Use a lawn mix that is labeled as suitable for Western Washington.
- Once sown, sprinkle the lawn mix with a light dusting of compost to hold in moisture and protect seeds from birds.
- Water lightly but regularly. Newly planted or reseeded lawns must be kept moist.
- Washington State University (WSU) King County Master Gardener publication; Lawns – Tip Sheet #11.
- Explore options for ecolawns as an alternative to grass.
- Oregon State University (OSU) Extension Service publication; Ecolawn: Less work and water.
- Rehabilitating an existing lawn:
- First, control any broadleaf weeds. This can be done manually or by using an herbicide labeled for lawn use.
- WSU website; Hortsense; Weeds.
- OSU publication; Weeds in Lawns.
- Use an aerator to improve drainage. By removing small plugs of soil, aeration increases the flow of water and air into the root zone, improving root health. Leave the plugs on the lawn to naturally decompose, adding nutrients to the soil.
- Dethatching can be done at this time if needed. Thatch is a dense layer of stems and roots which can keep water and air from reaching roots.
- Apply fertilizers suitable for fall. It’s advisable to do a soil test before adding fertilizer.
- WSU Snohomish County Master Gardener Extension Program publication; Soil Testing Resources.
- Look for “slow-release” on the label. Slow-release fertilizers provide nutrients over an extended period of time and can prevent fertilizer runoff.
- First, control any broadleaf weeds. This can be done manually or by using an herbicide labeled for lawn use.
- Acidic soils typical of Western Washington may also benefit from an application of lime in the fall.
- Do not add lime to a stressed or dormant lawn. A soil test will tell you what your lawn actually needs.
- Snohomish County publication; Natural Lawn Care.
- Do not add lime to a stressed or dormant lawn. A soil test will tell you what your lawn actually needs.
- Top dress with 1/4 to 1/2 inch compost, gently raking it into the turf.
- Overseed with seed suitable for Western Washington. Water in well, then cover with compost.
- For more lawn care tips and advice:
- WSU Extension publication; Home Lawns.

PLANT OF THE MONTH - September
Black-eyed Susan, Gloriosa Daisy
Rudbeckia hirta
(rud BEK ee ah HER tah)
Black-eyed Susan, Gloriosa Daisy
Rudbeckia hirta
(rud BEK ee ah HER tah)
- Looking for a plant to brighten up your garden? Rudbeckia offers vibrant daisy-like flowers from early summer to frost. It may still be available at a garden center near you. Or perhaps a friend has starts or seeds to share; it is easy to start from seed either now or next spring.
- Native to the eastern United States, this prairie/meadow flower has become widespread throughout North America.
- Supported by a sturdy stem, the 2–3 inch wide bloom has a dark chocolate-brown dome (though it can also be green) surrounded by rays of gold, orange, or a combination of the two. Some varieties add burgundy to the mix!
- Deadheading will promote continued bloom. Cut flowers are long lasting in arrangements.
- The stems and 3-6 inch, oval leaves are green and have hairy bristles, making them distasteful to deer.
- This short-lived, deciduous perennial grows 2-4 feet tall, forming clumps 1-2 feet wide. Rudbeckia will readily self-sow or spread by underground rhizomes, re-establishing itself and gracing the garden for many years.
- Hardy in zones 3-9, this sun-loving plant also does well in partial shade. Its water and fertility needs are moderate, and it is tolerant of most soils, neglect, and some drought.
- Bees, butterflies, and other pollinators love this plant, but it is resistant to most insect pests and diseases. It is relatively problem free; it even tolerates salt.
- For more information:
- Washington State University (WSU) Clark County Extension PNW Plants website; Gloriosa Daisy.
- University of Texas at Austin, Lady Bird Johnson Wildflower Center.
- North Carolina State Extension; North Carolina Extension Plant Toolbox; Rudbeckia hirta.
- Photo credit: Rudbeckia hirta; Vicki Sorg; Snohomish County Master Gardener