Below are many links to information about mulch, including several from Pacific Northwest government agencies. Explore these sites for lots of other useful information about gardening!

ABOUT MULCH, types, and uses--Cornell Cooperative Extension (NY)

Union of Concerned Scientists

King County (Washington) Solid Waste Division mulch info
Make the mulch of it!

WSU's King County (Washington) Extension Fact Sheets

INFORMATION FROM THE PACIFIC NORTHWEST (generally useful)
-- Saving Water Partnership (Seattle)
--Marty Wingate article from the SeattlePost-Intelligencer (11-15-2001)
--King Conservation District (Washington), manure share program

COMPOSTING COUNCIL OF CANADA:
Compost.org
MulchingPR

MULCHING TREES
--St. Lawrence County, NY:
Mulching Trees

Season All Season
Date 2008-01-03
Link to this record only (permalink)

Native Plants in the Coastal Garden (by A. Pettinger, 2002, p. 27), says the following about mulching Pacfic Northwest native plants:

...When an established native plant garden requires maintenance, it is usually minimal: mulching is probably the most important---and often the only---maintenance required. In any garden, mulching is arguably the most beneficial care you can give your soil and your plants. There are many advantages to using mulch. It suppresses weeds, conserves moisture by minimizing evaporation, and releases nutrients to the soil...Good mulch materials are compost, decaying leaves, well-rotted manures, sea kelp, mushroom compost, seedless hay or straw, shredded prunings, natural wood chips, grass clippings and evergreen needles and cones. Commercially available screened bark---usually referred to as bark mulch---has little to offer other than its ability to conserve water; it has no nutritional value and in fact depletes the nitrogen in the soil. When spreading mulch, don't pile it too close to stems of plants. If you are using compost as mulch, spread it about 2 to 4 inches deep. Other materials may be applied to a depth of 3 to 7 inches...

Season All Season
Date 2006-03-20
Link to this record only (permalink)

Both of these herbicides are registered pesticides, and the law requires that they be used in strict accordance with the directions (and only on the weeds/pests for which they are registered). It is safer for you and the environment if you manage weed problems without the use of pesticides.

You may wish to know more about these particular pesticides. Both Casoron and Preen are pre-emergents, meaning that they work to kill seedlings before they sprout. This means they will not eliminate weeds that have already broken through the soil surface and are growing above ground.

Casoron is persistent in both soil and water (i.e., it hangs around). Its active ingredient is dichlobenil. There are numerous environmental and health concerns associated with this chemical. Dichlobenil will kill any plants which are exposed to it, and will harm beneficial soil microorganisms. Below is a fact sheet about dichlobenil from Northwest Coalition for Alternatives to Pesticides

The active ingredient in Preen is trifluralin. It is a suspected carcinogen, and is toxic to fish and aquatic life, and earthworms. Here is more information from Cornell University and Pesticide Action Network UK.

The links below provide information about alternatives to chemicals for weed control. Northwest Coalition for Alternatives to Pesticides has a page of factsheets about specific weeds and ways to manage them. Here is their page on managing weeds in garden beds.

Washington Toxics Coalition also has information on ways to handle weeds in the garden. Here is more information in a PDF file.

Before reaching for chemical weed control, it makes sense to adopt gardening practices which will help keep the weed population low. Mulch is an excellent way to control garden weeds. After you manually remove weeds from an area of your garden, apply a layer of mulch. This should suppress weed growth and help retain soil moisture. Here is what garden expert Cass Turnbull says about mulch:

Not only does mulch retain water, smother tiny weeds and weed seeds, and make it easy to pull new weeds, it is also harder for new wind-borne weed seeds to get a foothold.

Mulch can be spread anywhere from 1 inch to 4 inches thick. The thicker it is, the more effective and longer lasting. Spread it thick in big empty spaces. Spread it thin around the root zones of shrubs to allow for sufficient air exchange, especially around shallow-rooted plants like azaleas and rhododendrons. And never let mulch stay mounded up in the base or the "crown" of a plant. It can cause crown rot on some shrubs and can kill them, even a year or more later.

Source: The Complete Guide to Landscape Design, Renovation, and Maintenance, Betterway Publications,1991.

Season All Season
Date 2008-01-12
Link to this record only (permalink)

Here is what Stu Campbell's book, Mulch It! (Storey Books, 2001) says about cottonseed hulls as mulch:

These hulls can be used most effectively around plants such as beans, which are suited to wide-row planting. Apply a 1- to 2-inch layer. Or you can wait until the plants have grown 3 or 4 inches high, then sift the mulch down through the leaves... Cottonseed hulls have a fertilizer value similar to, though not as rich as, cottonseed meal. Because they are so light, the hulls blow around in the wind.

Campbell discusses mulching asparagus with a choice of hay, leaves, straw, old manure, and compost for winter protection. You can leave these mulches in the spring, and the tips will emerge through the mulch. If you wish to extend your growing season, he recommends dividing your bed in 2 parts in spring. Mulch one half heavily with fine material like cocoa hulls, leaf mold, or ground corncobs. Leave the other half unmulched until shoots break through the mulched side. Then mulch the unmulched side. The half which was mulched earlier will bear a few weeks later than the other half.

The National Sustainable Agriculure Information Service has a web page on organic growing of asparagus crops which mentions other types of mulch (such as winter rye as a dying mulch and perennial ryegrass and Dutch white clover as living mulches) for this crop, applied at different times.

It sounds to me as if the main drawback with cottonseed hulls is their light weight. Otherwise, they should be acceptable as a spring mulch.

Season All Season
Date 2007-08-15
Link to this record only (permalink)

Spruce chips should be fine for mulching roses. Avoid letting mulch touch the main stem; the goal is to pile it on the root system away from the stem. You can remove it in the spring, or at least be sure that it's not too deep. While mulch protects from cold in the winter and drought in the summer, if it's too deep, water cannot get to the root zone of the plant.

I can't recommend Preen, as I have never used it. I avoid chemicals, as I find that you have to pay more attention when you use them than if you just wander through the garden now and then and pull all the weeds you see.

Pre-emergent weed controls like Preen never provide complete weed control. The most important thing to do is weed the area first, as pre-emergents only control weeds that have NOT sprouted. And if you have lots of seeds in the soil, don't expect the Preen to kill them all. If water is required, beware of too much water (i.e., rain) that can wash away the herbicide. Read the directions carefully if you try it!

Rather than use a chemical, I would weed the area now and then apply mulch. In addition to protecting the roots and soil, the mulch will suppress weeds, possibly until spring. You will have to watch for weeds that do sprout and be sure that you don't let them go to seed. Otherwise, you will set yourself up for lots of future weeding. Chemicals don't really help in situations like that, as you have to time their application perfectly. Hand weeding and mulching--well timed--can work better than an herbicide. Mulching, of course, has additional benefits.

Season All Season
Date 2007-09-07
Link to this record only (permalink)

Your mulch is unlikely to harm your bearded (rhizomatous) irises, as long as it is less than one inch thick over the rhizome tops and allows air through. Here is some information from The Gardener's Iris Book by William Shear: "How deep should the rhizome be set? That depends. In light-textured soils, it can be covered by as much as one inch of soil, but for average to heavier soils, the top of the rhizome is best left exposed to the healthful influences of sun and air. Remember that the rhizome is a stem, not a root, and needs to breathe!...If you do apply a mulch, it must be loose and airy, so it won't pack down and get soggy--a sure ticket to rotting rhizomes in the spring." Shear suggests pulling back the mulch in spring (since it is for freeze protection in his mind), but it seems to me that would defeat your purpose. You might meet both goals (moist soil and dry rhizome tops) by mulching around the irises but not right on them.

Season All Season
Date 2009-03-12
Link to this record only (permalink)