The Magic of Mulch

When I do consultations, I get a lot of questions about mulch. First of all, what IS mulch? Is it compost, bark, what?

The answer is that mulch is a blanket - it is any material that you use to cover the bare soil in your garden beds. It could be compost, bark, fallen leaves, pine needles, a composted combination of sawdust and manure, even rocks or crushed glass (I do not recommend the last choice in particular, but I have seen it done) - anything that covers the soil while allowing water and air to penetrate.

Mulch is usually applied in a layer 1-1/2 to 2" deep. This depth will help hold moisture in the soil so you won't have to water as often. It will also do a good job of keeping weeds under control. I believe that weeding without mulching is a waste of your time. When you have weeded and loosened the soil, you've created a perfect place for weed seed blowing by on a spring breeze to land and germinate. A thick layer of mulch is not as "germination friendly" as your freshly worked soil, so it keeps new weeds from getting established. If there is already weed seed in the ground, which is often the case in areas that have been weedy for a long time, it has trouble germinating if it is smothered by a good layer of mulch.

Heather bed before weeding

When people tell me that they used a mulch "but the weeds came right back," it's because one of two things happened.
1) They didn't put down enough mulch. A mere half inch is not enough.

Heather bed after weeding and mulching with Steerco

2) They failed to weed thoroughly. If the roots are still in the ground, the weeds will regrow quickly. Pulling the tops off isn't weeding. You have to use a hand cultivator or soil knife and grub out those roots. In areas that have long been home to weeds, a couple of seasons of diligent weeding will be necessary to get things under control. Each year will be easier and by season 3, you'll be pleased to see how quickly you can get your beds weeded and looking good.

OK, now you know why you should use a mulch. So the question is: which one? A lot of people use bark, but I don't recommend it. Bark is not composted. After you spread it out over your garden beds, it will start to break down and as it composts itself it takes nitrogen from the soil to complete that process. That means there is less nitrogen available for your plants to use and they end up stressed. Notice the leaf color on plants sitting in a sea of bark. The leaves are often yellowish instead of deep green - and that's because they lack nitrogen. To keep that from happening, use a mulch that has already been composted.

(That said, I do like bark as a place holder. If you have a spot overrun by weeds that you plan sometime in the future to turn into garden space, weed it well and put down a thick layer of bark. It will keep the weeds down and when you are ready to use the space, you can plow the composted bark into the soil. Thick layers of coarsely chopped bark also make fine garden paths between raised beds.)

That narrows the choice down to compost (homemade or commercial) or products like Steerco and Gro-co. Steerco is a combination of composted sawdust and steer manure. Gro-co is composted sawdust and municipal sludge (in other words treated and composted sewage). Some people have no problem with Gro-co, others are creeped out by it. It is completely safe. The only possible objection I might have is that there might be a higher (but still very small) concentration of heavy metals in it.

My preference is Steerco, sold in Seattle by Sawdust Supply, the company that provides all the soil and mulch for the Northwest Flower and Garden Show. I've used countless yards of this material in the past 20 years and have always been happy with the result. It is already composted and contains microorganisms that perk up tired garden beds. It helps add structure to sandy soils and loosens clay soils - provided that you make it part of your annual bed clean up and maintenance. It does all the things you want a mulch to do, plus it has no odor and it looks great. It makes the humblest garden look professionally done.

On top of all that, Steerco is a bargain. A bag weighs somewhere in the neighborhood of 75 lbs. and costs about $5, including tax. Steerco is also available by the yard. You can pick it up yourself or have it delivered.

If you need to figure out how much mulch, bark or topsoil you need for a project, here's a handy chart.

5 Things To Do In The Garden In Fall

Fall color in the Arboretum at South Seattle
Community College

It is raining in Seattle today - a slow, soaking rain. After this kind of rain, the weeds are easier to pull and the wet leaves rake nicely into a pile that stays put until you get them into the compost or yard waste bin. 


I love gardening in the fall. The temperatures are cool so I don't get overheated when I work.  Fall is a long season in Seattle with three full months of color, and being outside, watching the landscape change is good for the soul. 

Here are 5 things to do in the garden now:

1 - Tidy up. Start by clearing away dead foliage on perennials. Rake leaves. You may have to do this a couple of times before fall is over because don't plants go dormant here all at once. Do a thorough weeding job - you will thank yourself next spring. 

2 - Mulch beds. Most horticulturalists will agree that mulching in fall is a good idea. But we don't all agree on the best way to do it. Some people rake piles of leaves into their planting borders and call it good. I prefer to use a composted product like Steerco  (available from Sawdust Supply in Georgetown). I've tried the leaf method and found that after a lot of rain, the leaves stick together, forming a solid mat that smothers ground covers. If the leaves aren't raked off of the crowns of perennials early enough in spring, the new shoots go off in strange directions and the plants fail to do well. Steerco, on the other hand, provides a blanket that protects plant roots from the cold while allowing air circulation. It also looks a lot better. 

3 - Winterize sprinkler systems. It seems obvious that sprinklers should be shut off in the fall, so I am surprised by how many people overlook this necessary chore. Sprinkler lines are shallow and often burst in cold weather. This creates a big problem, and not just for the homeowner, as this mudslide story on the West Seattle Blog from last December shows. 

4 - Plant trees and shrubs. This gives plants a head start on next year. Root systems will start getting established well before the busy growth season in spring. As an added plus, local nurseries have terrific plant sales going on right now.

5 - Plant spring blooming bulbs. If you want daffodils, crocus, tulips and hyacinths next year, you have to plant them now. 

Here's the Dirt: on Soil, Compost and Mulch - Introduction

When you go to a garden center, you'll find lots of bagged goods with names like potting soil, planting soil, top soil, bark, fine bark, play chips, compost, mushroom compost, planting compost, etc. There's chicken manure and steer manure and bat guano (more manure). Some companies sell three-way and five-way mixes of various ingredients that claim to be excellent growing media.

With so much available, how do you choose which, if any, of these products are right for your garden? The first step is to understand what these materials really are. There's a lot to say about some of them, so I'm going to do a series of posts to tell you about soil, soil amendments, compost and mulch.

First up - soil. 
Soil, also called dirt, is the foundation of your garden. The health of your soil determines the health of the plants you grow. If you are at all serious about gardening, particularly if you plan to grow some of your own food, you owe it to yourself to learn about the soil you have and how best to maintain its tilth or health.

Technically, soil is a combination of sand, silt and clay particles with some amount of organic matter mixed into it. There is no precise recipe for soil. The soil you have is the product of the wind, weather and geology of your area.

Thanks to the action of glaciers long ago, soils in the Seattle area are varied. Some of you are gardening in sandboxes. Some of you are trying to break up clay. If you are gardening in an area along a river, you might have silt. Many of you are finding rocks the size of your fist nearly everywhere you dig. All of these scenarios are the gifts of what is called "glacial till."

The combination of sand, silt and clay particles you find in your garden is what makes up the structure of your particular batch of soil. Organic material comes and goes over the seasons. Nutrients and water are taken up by plants. Depending on the health of your soil, microscopic organisms thrive or struggle. Through it all however, year after year, those sand, silt and clay particles remain, providing the stage where all the rest is played out.

There are many things you can do to improve your soil, but there is nothing you can do that will change the type of soil you have. A clay soil, for example, cannot be changed into sandy loam, no matter what you add to it. (In fact, as I'll explain in a later post, adding sand to clay is a bad idea.) Your best bet is to know what type of soil you have, what its characteristics are and how to make the most of what you have.

In Part 2 of "Here's the Dirt," I explain more about soil types.

Wondering how much mulch, soil or compost you should buy for your gardening project? Check out this handy table.