(Ed. Note: Wallyhood welcomes Jeanie Taylor as our new contributing writer, focusing on gardening. Jeanie owns Taylor Gardens, a gardening coaching service and Wallyhood sponsor, holds a B.S. in Botany, an M.S. in Conservation Biology , and teaches workshops for home gardeners on propagation and sustainable gardening. If you have questions on gardening, please e-mail her at firstname.lastname@example.org and she’ll try to answer them here. Welcome, Jeanie!)
Welcome to the inaugural Wallyhood Garden Questions column. I am pleased to be taking questions that will enrich the lives of Wallingford gardeners – or at least bring up some interesting ideas to discuss.
Mike and Linda ask, “We want to know about moss in the garden. What causes it and what are suggestions for dealing with and preventing it? For now we scrape the moss off the topsoil and then work up the soil.”
Although your choice of words – “cause” and “preventing” – seems to indicate a distaste for moss, I hope to win you over to another view! I find that a lot of problems in the garden, as in life, are the result of expectations. We expect to have a garden that looks a certain way, and when we observe things we don’t expect, we get uncomfortable. Moss shows up unbidden; it seems out of place – it’s not part of the plan.
A few moss facts:
Any particular moss species doesn’t grow just anywhere. Different species have preferences: bare soil, wood, concrete, rocks, surfaces that are acidic or alkaline. Thus, moss can be used as an indicator of your environmental conditions. On the plus side, it thrives where others cannot – cool, moist, shady spots where some plants (notably lawns), suffer.
This garden (ok – it’s Mike and Linda’s actual garden) has one species on bare soil that has flat, ferny stems and another on the concrete along the bed with spikey tree-like whorls.
The shrub bed below contains an old concrete or asphalt curb colonized by moss, but the woodchips in the bed are moss-free – they don’t support the masonry-loving moss.
Mosses have no vessels for conducting water and nutrients, and no true roots like trees or flowering plants. They’re in a group called bryophytes that absorb all their water and nutrients through their leaf and stem surfaces, and pass them along cell to cell. This requires a constantly moist environment, which is why they like shady, moist areas. In summer heat, mosses just go dormant and wait for the fall rains to begin growing again.
Moss is not harming the surface it occupies; it just uses it as a place to exist. On roofs and structures, moss can be a problem because of its moisture-holding abilities, and because of the other things that tend to live with the moss. For that reason it may facilitate rot.
Mosses are valuable for biodiversity and healthy ecosystems. They are a pioneer plant on bare, disturbed, or burned over ground, rocks and wood. They facilitate soil formation, covering bare soil like a band-aid to protect it and prevent nutrient loss, and allow beneficial organisms to reside there.
Beneath this moss I have peeled back, you can see a couple of tiny holes, that indicate soil dwellers are using the moss as protection.
If you have bare soil, something will want to move onto the empty real estate – why not moss? It is actually trying to help you out, and it’s free!
Now I will descend from my soapbox and get down to specific ways to deal with moss, either as a problem or an asset.
Two approaches to banishing moss are 1) to repeatedly remove it, or 2) to permanently change conditions so it is not favored. If you want to permanently get rid of it, investigate:
1) drainage 2) shade 3) pH 4) nutrients, high or low and 5) possible soil compaction (which leads back to #1).
You may be successful with these strategies:
- correct water flow to a low spot where water collects
- reduce shade by thinning trees appropriately
- add organic matter to boost nutrients to poor soil, or stop adding too much nitrogen or other fertilizer to soil that doesn’t need it
- and use organic matter or reroute foot traffic from an area to correct compaction. Wood chips or leaf mulch will cover the soil and may take the place of moss, at least for awhile.
Every situation requires site-specific remedies. Any effort to change in pH will likely be temporary in our climate, with our soils. On roofs or sidewalks you may be able to improve air circulation and let in more light in by thinning trees appropriately, but some areas will need regular cleaning.
A word about chemicals: be extremely careful with chemical remedies. Zinc and copper are sometimes recommended, but copper has been shown to be highly toxic to salmon in tiny amounts, and zinc is also toxic in aquatic systems. I don’t know any way to prevent some of the residue from eventually finding its way to the street and storm drain, which leads to Lake Union or Puget Sound.
There are some products that are less problematic: insecticidal soaps labeled as moss killers that are the same formulas that organic gardeners use on insects. Even if you kill the moss, it will need to be removed after it dies, so it might be less labor-intensive to just have it scraped or washed off your roof a couple of times a year if you can’t change the environment that encourages it.
A creative way to deal with moss is to work with the conditions you have: plant a shade garden or rain garden that incorporates moss, using plants that require the same conditions, and be the envy of those who don’t have the right conditions for your special garden!
Moss gardens are in a special horticultural category. You can visit one locally at the Japanese Garden in the Washington Park Arboretum (or check out these lush photos taken by a visiting gardener. If you want to create your own, George Schenk’s book is the place to start.
For ALL things moss, check out this link http://bryophytes.science.oregonstate.edu/mosses.htm