Dr. Linda Chalker-Scott is an Extension Urban Horticulturist at Puyallup Research and Extension Center and Associate Professor and Horticulture and Landscape Architecture at Washington State University.
She is also a member of the highly acclaimed Garden Professors.
Here are some of the highlights…
Dr. Linda Chalker-Scott (L CS) “Mulch is anything that covers the soil – some are good, some not so good for lots of reasons. And lots of myths about them!”
Many people get confused about amendments and mulch. For the record, what is the difference between them?
A mulch is simply a topdressing. An amendment is worked into the soil. So compost can be either one.
And what are the benefits of mulching?
So many benefits! Moderates soil temperature, reduces erosion and evaporation, and organic mulches have more.
Organic mulches also increase soil nutrients and soil biodiversity. Love them!
And I like to consider wood chip mulches as “slow food” for soil. Much better than the fertilizer fast food.
Deep, coarse organic mulches are the BEST weed control mechanism out there.
One of the most frustrating myths is that wood chip mulches rob your soil of nitrogen. Absolutely not true!
The microbes do use nitrogen right there at the soil surface – but not underneath where roots are.
And how what about the depth of mulch?
For chunky, woody mulches, the more the better in terms of weed control – up to 18″ have been used!
The tipping point: organic mulches of 3” or less will promote weed growth, while 4” or more will suppress it.
[p.s. compost used as a mulch will grow weeds, no matter the depth…coarse organic mulch is the best weed control]
And just to continue this thread, fine textured mulches can be damaging if they’re too deep.
Wood chips are the best! We try to avoid having them touch the trunks, although new research may change that.
But many gardeners worry about using wood chip mulch because of termites and mice. Do wood chips attract termites and mice?
Termites hate wood chips – in experimental taste tests they only eat them if nothing else is available!
Termites like nitrogen and phosphate-rich mulch. Wood chips have neither.
Given a choice, termites would rather eat nutrient-rich mulches; they’ll settle for cardboard but they avoid wood chips.
Mice don’t really care for chips either. They collapse into burrows. Rodents love tunneling under sheet mulch
And she tackled the garden media darling “lasagna layering” of mulch
Be careful of the “lasagna mulch” approach. Layers of paper restrict water and air movement to the soil.
Lasagna mulching may appeal to your emotions, but it doesn’t do much for the air and water content of your soil.
And I’d also caution people not to use too rich a mulch. It can contribute to nutrient pollution.
And addressed the issue of mulch transferring disease!
Research has shown that disease isn’t transferred from mulch to healthy trees. Unless there’s a splash issue
In choosing the right mulch…
In drier areas inorganic mulches are often a better choice. Rubber, not so much. I’ll elaborate.
If the EPA defines discarded tires as pollution, then why isn’t recycled rubber mulch in the same category?
Leaves are great [mulch], as long as you shred the big ones. Layers of big wet leaves restrict air movement to the soil.
And using mulch to change pH, much to everyone’s chagrin the answer was…
Wood chips, bark and pine needles will not acidify the soil.
Unless you’re working with container plants, mulch will not change the soil pH. The soil profile is HUGE outside
There’s been quite a bit of research looking at this. pH is determined by a lot of climatic factors.
Rainfall is very important in determining pH, because microbes need water for decomposition, which changes pH.
To wrap it up, I am giving you an opportunity to win two of Dr. Linda Chalker-Scott’s books. Great Xmas gifts!
To enter the competition, write a comment below and let me know what kind of mulch you use. One lucky gardener will win The Informed Gardener and The Informed Gardener Blooms Again, courtesy of THE REAL GARDENER.
Draw on November 30.
The lucky winner of the draw is Chris Sabbarese. Congratulations, Chris!