Mulch Matters

Brunnera 'Jack Frost'

The organic mulch around this moisture-loving Jack Frost Brunnera will keep me from having to water it as often in the summer time and will cut down on my weed pulling duties.

First, the basics: a mulch is anything that is placed over soil generally for the purposes of inhibiting weed growth, insulating the soil, conserving moisture, and contributing to the aesthetic value of a garden.  The most common mulches are organic ones, that come from dead, or dying, plant materials, but there are also inorganic mulches, such as rock and plastic, that also can be useful in certain situations.  A mulch can also provide the added benefits of reducing the spread of pathogens, preventing erosion, and reducing heaving – when freezing and thawing of the soil pushes up unestablished plants.

With that said, there’s a whole lot more to mulching than meets the eye.  There’s much to mulch, if you will.  Different gardening conditions may call for different types of mulches, or possibly no mulch at all, and deciding how to mulch will also depend on your gardening goals and possibly the availability of the mulch, budget and more.  Don’t worry, this is not meant to be an exhaustive writing on mulch, but I thought I would share some things that I think are the most important and relevant rules of (green) thumb for mulching.

Anytime is an acceptable time to apply mulch, but it may make most sense to do so in the spring or fall when most weeds are sprouting.  You may also want to bear in mind the effect the addition of mulch will have on the soil temperature as well.  When added in spring, the soil will take longer to warm up.  When added in the fall, the soil will remain warm for longer.  When applying mulch, generally a thickness of 2 to 3 inches of the mulch is desirable.  The needed thickness can vary depending on the density and weight of the particular mulch used, but generally this is thick enough to keep weeds down, insulate the soil, and conserve moisture, but not so thick that it will stress plant roots, or prevent the lighter rain showers from reaching the soil below.  You should only need to reapply mulch when the mulch has decomposed a bit into the soil and is no longer fulfilling its mulch duties.  Depending on what material is used, people that add mulch every year may end up adding too much mulch and stress surrounding plants.  Another benefit of mulching around trees or woody plants is that it will keep grass and weeds away from the trunk, keeping you and your mower/weed wacker also away, which are common causes of injury to trees.  However, it’s very important that you keep the mulch about 6 inches or so away from the trunk.  You do not want to pile any organic mulch right up around a plant’s trunk, as it is an invitation to disease and rodents, among other potential problems.

One of the most common organic mulches available is shredded bark or the larger bark chips.  WSU has a great article on wood chip mulch here.  Avoid using mulches with dyed bark or that are exclusively the large bark chips (chunky style).  The large chips will take a very long time to decompose and also don’t suppress weeds as well as a finer-textured mulch would.  The best mulch is one that is able to improve your soil over time.  A fine-textured organic mulch will help improve your soil texture as earthworms and helpful microorganisms and fungi break it down and incorporate it into your soil.  This protective layer of mulch will also help prevent the pounding rains from compacting the soil, and keep the soil from developing a hard, outer “crust”, which can lessen water absorption and create more runoff.  Bear in mind though that as an organic mulch breaks down it will deplete some of the nitrogen from the top part of the soil, so this could have an effect on shallow-rooted plants, such as groundcovers, annuals or vegetables.  Amending or fertilizing your soil properly beforehand will help, or simply keep the mulch further away from plants that are shallow-rooted or not yet established. Grass clippings can also be used as a mulch, although many people may not like the look of grass clippings as such, and it would require continual replenishment.  You would not want to use this as a mulch if there are grass or weed seeds in the clippings.  I’ve heard from some gardeners that grass clippings are great for their vegetable gardens.  A leafy vegetable, such as lettuce or kale, would benefit the most from a nitrogen-rich topdressing in which your main goal is to get the plants to produce lots of foliage and quickly.  However, when the weather is dry and you’re not cutting off more than a third of the grass blades at a time, I’d recommend just leaving the clippings on the lawn to keep that fed organically.

One of the best mulches you can use is compost.  A good compost will add macro and micro nutrients to your soil, as well as beneficial organisms, and will incorporate rather quickly into the soil.  Regular topdressings of compost is one of the best things you could do for your soil.  A happy soil makes for happy plants.  And, as Bob Ross has attested, our landscapes will all benefit from having happy trees.  The downside to using compost, however, is that it is not the best mulch option for preventing weed growth for a long period of time, so it may need to be applied somewhat regularly to keep them down.

Groundcovers can also be used as a mulch and may be one of the better options at improving the aesthetic value of a garden.  The ones referred to as cover crops or green manures can do wonders to help improve soil quality.  Legume cover crops, such as vetch or crimson clover, have the ability to fix nitrogen into the soil, feeding nearby plants.  Cover crops are usually tilled into the soil to create a fertile tilth, which should be done a couple weeks prior to planting your vegetable or fruit garden, wildflower meadow, laying of sod, etc.  Cover crops can work great as a temporary mulch.

Hosta 'June'

This beautiful Hosta was completely eaten this last winter from the bottom up.

One of the only downsides to using an organic mulch is that it can attract slugs, snails, rodents and other pests, depending on the material used.  Since we’ve moved into our home in 2009, I’ve been busy adding beds/borders to our yard and amending them with organic matter.  Of course the moles love to dig in this earthworm-rich, friable soil, as opposed to the hard clay we have elsewhere, and we now have a pretty large network of mole tunnels throughout our yard.  In hindsight, I really should have been much more diligent about chasing them off the property.  At the time they were starting to become more noticeable, I had just read an article on moles from a local gardening source about how they often got a bad rap.  Yes, they loved to eat worms, but for the most part they would leave your plants alone and help with soil aeration, so it said.  Well, apparently I also needed a lesson from the school of life, as I later discovered that voles and mice will take advantage of a mole’s hard work and travel through these underground “highways,” and they may not be as kind to your plants, as they stop for nearby snacks along their route.  Unfortunately, an organic mulch layer also provides opportunity for the voles and mice to more easily dig their shallow holes to get closer to plants to eat them.  This last winter I lost seven Hostas and an ornamental grass, ‘All Gold’ Japanese forest grass, to voles or mice.  These plants were mostly eaten from the bottom up and were in areas that were well-mulched and that had nearby mole tunnels.  Some gardeners have had more luck when they’ve removed the mulch layer, which I plant to do in the winter time around the Hostas.  It may also be helpful to enclose the root ball with hardware cloth when planting Hostas, or any other plants that you are concerned may be eaten by these critters.  With that said, certain mulch materials will actually help repel some pests.  For instance, cockroaches, ants and termites, among others, do not like cedar chips because of the chemical Thujone that they contain.

I generally would not recommend using an inorganic mulch, but there are some circumstances when they might be appropriate.  Black sheets of plastic work very well to warm the ground up, and I’ve seen this method used in lavender farming.  Rocks or boulders seem to be essential to a landscape.  Rocks may be useful as a mulch as they too can help warm the soil, and small rocks could provide for better drainage around a plant’s root crown, an area susceptible to rot.  I would never recommend using the rubber mulches that are shredded/ground up and meant to look like organic ones.  Think of your mulch as a soil enhancer and as potential worm food and this will steer you clear of the ones that are not so garden worthy.

You may also need to take into consideration the effect a particular mulch may have on your soil’s pH, however, it seems the importance of this caution may be exaggerated by many.  New studies are showing that even though a mulch substance can have an extreme pH level, such as oak leaves and pine needles/straw, which have a very acidic or low pH level, they do not have a substantial effect on the soil’s pH, at least not at the root level of most established plants. I hope this information is helpful to you.  I’d love to hear any tips that you might have on mulching.


A Million Leaves a Leavin’

These native Cottonwood and Red-Twig Dogwood trees will soon be putting me to work…

It’s that time of year again when my hopes start to rise thinking the more mundane chores of gardening will soon diminish.  And then the sky starts to fall.  With many of us having yards blanketed by leafy litter this time of year, what’s the best way to deal with it all?   Do you leave it?  Bag and trash it?  Move it to your borders and garden beds?  Add it to the compost pile?

Successful gardening is a lot of trial and error as you discover what works best in your yard, region and for your purposes.  I learned that you should not assume all gardening and landscaping advice is widely applicable, even for the seemingly innocuous.  In certain areas of the country one method may be useful and in other areas it may deliver much different results or come with additional unwanted consequences.  Seek local advice.

Quite a few years back I was reading an article in a national gardening magazine about a California gardener who took a more natural approach to gardening.   She recommended just moving any fallen leaves to the nearby garden beds and borders so they could decompose back into the soil, feeding the nearby plants and temporarily acting as a mulch, keeping plants warmer over the winter time and also reducing weeds and heaving.  Yes, fuel the soil web, reduce weeding, less work…  I’m sold!  I didn’t mind so much that my borders weren’t that “clean” or clutter-free.  When spring came though I soon discovered why this may have worked better in California than here in the Pacific Northwest.  Slugs were in a surprising abundance that next year.  It turns out those leafy layers acted as great slug habitat, for cover and for laying their eggs in (which look like small pearls).  My young, evergreen Solomon’s Seal clumps (Disporopsis pernyi) did not stand a chance.  Even putting slug controls around these plants once I noticed was not enough to stop their onslaught, and the plants met their demise.  My hostas and false lily of the valley (Maianthemum dilatatum) also suffered a bit, among some others.  If you happen to have a more slug-proof garden and want to go this route just be sure to rake away any leaves over your perennials before they sprout in spring to avoid any chance of disease being spread.

However, even with the unwanted company of all those goopy gastropods, this is still a method I use, I’ve just restricted this practice to one portion of our yard now, because for that particular area the pros seem to outweigh the cons.  It’s the area behind our house near the forest edge, which in spots is a seasonal wetland.  I’ve pulled out many of the invasive blackberries that were back there, but without new plants to replace them, and not enough money for mulching the whole area just yet, I’ve decided it would be best to leave the soil covered from fall ’til spring so the leaves can act as a mulch, protecting the integrity of the soil texture from the pounding rains.  Another big deciding factor for this was the birds.  There are lots of birds, including the American Robin, Varied Thrush, and Northern Flicker, that love to rummage through the leaves on the ground looking for insects or other goodies, even slugs, to eat.

Japanese Maple leaves and Lysimachia paridiformis

One leaf containment method I would recommend avoiding altogether is bagging the leaves up and throwing them in the trash can.  That’s removing them from the life cycle at the time when they are ready to give back.  I think we should garden more responsibly than that.  If you don’t yet have one, check with your local waste management company about getting a yard debris bin so they can compost the leaves for you, or compost them yourself, which is what I would recommend.  Being in a large pile the leaves will decompose faster than when they are spread throughout your garden beds anyways, then you can use the leaf mold, or compost, wherever needed.  Yes, you will most likely still attract slugs, but with more vertical piling the affected area will be less (Just remember, they’ll appreciate any moist, protected area, such as under wood or stones).  To make things easy I try to fit in one last mowing for the year after a lot of the leaves have fallen so I can add them and the grass clippings to the compost pile at the same time, if the weather is dry enough for my mower to handle this.  More on composting in a future post.

If you’re wanting to kill some sod to make room for new garden beds, piling the leaves where you want them should kill the grass in time for next spring (so don’t leave them on the lawn for long if you are not going for this same result).  If this is in a windy location though it may be a little tricky keeping them right where you want them.  If you have any bird netting from your berry bushes or fruit trees you can roll that over the leaves and secure the corners.

Also, keep in mind that certain plants can be killed, or poorly affected, if they are covered by leaves for too long (primarily low-growing evergreen or semi-evergreen plants), such as the common Scotch or Irish Moss, and, as happened in my own yard, some of our native sedges.

Whichever method you choose, be sure to make a gigantic leaf pile first for the kids or grandkids (or yourself) to play in.  Getting the kids involved in these chores is a win-win.