Three Things You Can Do:
Reduce Seed Rain: Cut “survival rings” around infested trees. Ivy goes to seed (see photo: prior page) when it climbs vertically, so severing vines at the base of trees (or anywhere ivy is fruiting) will prolong the lives of trees and slow ivy’s rate of spread.
Do this for clematis vines, too (pictured right: Clematis vitalba, aka “old man’s beard). Don’t pull vines off; it could damage the tree and endanger you. Let ivy and clematis “wither on the vine” and come down on their own.
Girdle English holly and laurel (saw a ¼ inch “kerf” around the stem at breast-height), and keep hedges well-pruned so they don’t set seed. Holly and laurel will resprout, so break off new shoots to eventually starve the plant – this may take years. If you want faster results and have weighed the risks and benefits of herbicide (see below), and if you’re not in a wetland or slide-prone area (check Environmentally Critical Area status), you may apply glyphosate (active ingredient in Roundup) to a fresh cut (kerf or “frill”) into live bark on the stem – in dry conditions but not during summer dormancy (read the label and apply herbicide on your property only). Leave holly and laurel upright as dead snags for wildlife perches or until tops die to prevent branches from re-rooting. If invasive holly or laurel are holding the soil and preventing landslides, seek professional geotechnical advice. Often, such advice suggests you supplant invasive root structure with native trees and shrubs while pruning (not immediately killing) invasive plants at a rate that native plants can establish (5-plus years).
Other Western Washington invasive seed rain sources include: Portuguese laurel, pyracantha, cotoneaster, English hawthorn, sweet cherry, wild plums, European mountain ash, and Japanese honeysuckle. Knotweed is an invasive threat that spreads primarily by root/plant fragments, neglect of existing stands, or yard waste dumpings. Knotweed can severely degrade salmon habitat and is almost impossible to eradicate without careful applications of herbicide by licensed professionals.
Please note that glyphosate is a wetland-safe herbicide that is four times safer than aspirin (acute toxicity), is considered “practically non-toxic” by the EPA, and is reportedly the safest herbicide available for humans, pets, fish and wildlife – safer than alcohol, most household products, and many pollutants we pour into our bodies, homes, cars, and atmosphere daily. The inert ingredients (surfactants – oils or detergents that help the herbicide penetrate leaves in foliar sprays) of some over-the-counter herbicides are more toxic to fish and amphibians than the active ingredient. For bureaucratic reasons, wetland-safe glyphosate formulations may only be available to licensed professionals. To weigh the risks of herbicides, go to National Pesticide Information Center or search for academic reviews on “glyphosate” at Extension Toxicology Network.
We agree that it’s preferable to reduce the quantity of herbicide used in farming and lawn care, and that this could be accomplished by establishing healthy native plant habitat that offers natural checks and balances – the goal of organic methods. But, the amount of toxins that will get into our waterways, Puget Sound, and the food chain (meaning us) may be far worse if we reject herbicide tools that help preserve forest canopy and topsoil (stormwater’s natural sponge and filter) that are critical to filtering environmental pollutants.
Increase Evergreen Tree Cover: Plant native conifers (Douglas fir, Western Red Cedar, Western Hemlock, Sitka Spruce, Grand fir, Shore Pine) in appropriate properties (avoiding overhead and underground utilities), or join an organized volunteer group doing the same in public parklands. Cut circles in ivy patches and periodically “knock back” blackberry (cut down to approximately two feet) enough to plant, leaving most soil undisturbed. Planting trees in November next to rotting logs/woody debris – or mulching with arborists wood chips – will reduce watering needs, but monitor plants their first two summers and water accordingly (approx. 2 gallons / week July-Sept). After conifer establishment, plant native shrubs and groundcovers (in some cases, staking 2 ft-long, 1 in-diameter willow branches years prior to conifer planting can help tree establishment). Also, consider replacing invasive hedges with native plants such as: evergreen huckleberry, California myrtle, silk tassel, tall Oregon grape, and others. Inexpensive bareroot plants can be ordered (every January) through King Conservation District.
Enhance forest “sponge” capabilities to preserve the health of Puget Sound: The potential loss of Seattle forests will exacerbate stormwater pollution (rain run-off from roads and lawns), the #1 source of toxins fouling Puget Sound. Consider replacing your lawn with a raingrarden to capture and absorb rainfall from your roof. You may also increase the “sponge” of healthy soil by leaving appropriate organic matter (tree trimmings, grass clipping) on site, or ask local tree services for arborist’s woodchips to mulch trees and perennial beds (keep woodchips 4 inches away from plant stems). To avoid causing slides, don’t pile yard waste on slopes or dispose of it in parks (it may introduce invasive weed seeds into our natural areas). An excellent summary of “green infrastructure” to reduce stormwater can be found at Tox-Ick.org.