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Good Growing

Mulching and Wood Chips

There are many times people will call with questions about what they can do to help their trees grow better (cultural practices) or what they can use to help keep weeds out of the garden. One of my suggestions always is mulch. Now it should be stated that mulch is just one component of good cultural practices in landscaping and gardening, especially with trees, but mulching is definitely an important one.

What benefits does mulch provide plants?

  • Helps to moderate soil temperatures
  • Helps to maintain even soil moisture
  • Helps to minimize soil erosion and runoff
  • Reduces weeds by minimizing weed seed germination
  • Keeps lawn mowers and weed whips away from trunks of trees and other woody ornamentals preventing mechanical damage
  • Overtime adds organic matter back in to the soil as mulches break down

In that last bullet point – see where I mentioned organic matter? Almost all of these major benefits of mulch are only provided by organic based mulches. I never recommend using mulches such as rock or rubber mulches around plants or in the landscape as they don't assist in moderating soil temperature or soil moisture and don't add organic matter to the soil over time.

So if you shouldn't use rock or rubber mulches what can you use? Shredded hardwood, shredded cypress, arborist chips/wood chips are all good choices. You can find chips from local tree care companies, municipalities, or electrical companies. Wood chips may be a better option as landscape mulch for a variety of reasons including variety of size of the chips and rate of decomposition to name a few.

According to Linda Chalker-Scott from Washington State University "wood chips supply nutrients slowly to the system; at the same time they absorb significant amounts of water that is slowly released to the soil. It is not surprising that wood chips have been cited as superior mulches for enhanced plant productivity." She further states that wood chips have been found beneficial in establishing woody plants in urban and disturbed planting areas.

When applying mulch, apply mulch 2-4" deep for hardwood shredded and cypress and chips can be mulched 4-6" deep but which ever mulch you use, keep a small space between the mulch and base of the plant. For best weed seed germination control – apply mulch before weeds germinate, if you missed that window, mowing the weeds extremely low and then applying mulch can be an effective way of smothering weeds that have germinated. It should be noted that just because you mulch it does not mean that you will never have to weed again – it will be easier if incoming weed seeds germinate in the mulch making pulling them much easier than having to pull them up from bare soil. If mulches are applied too thin, then weed control becomes ineffective. Reapply mulches as needed as they begin to breakdown to maintain recommended mulching depths.

So if you've been wondering whether or not to mulch around trees or shrubs or in landscape beds – the answer is a resounding yes.