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Mulching Clay Soil
I have butterfly garden w/all native MN plants in my back yard.
It is along the north side of a south fence, so it gets about 4-6 hours of sun a day. I have plants that are suited for wet mesic soil.
What I am wondering is, I would like to mulch to keep weeds under control but am nerveous because the soil is clay like and is always somewhat damp and moist.
Should I mulch? If so what kind of mulch, shredded bark, bark chips, etc? I would like to keep it natural looking and enviromently friendly. If I shouldn't mulch, what should I do to keep weeds under control?
Doug says
Well, mulch on wet soils will keep the water in.
I wouldn't be putting it over top of the crowns of most plants but rather holding it back from them by 6 inches or more.
Watch For Snails
It will also encourage snails and these can be a major problem under a well-mulched damp clay soil. If you chose to mulch, you'll have to get some E-scargot or other iron-phosphate based solution to control this pest.
Compost and compost-tea (particularly compost tea) has an interesting side effect in that weeds tend not to like soils that have high bacterial and fungal counts.
There's increasing research that suggests weed problems slow down as the compost tea applications increase.
Kind of Mulch
The kind of mulch you use depends on what you like the look of and what you can afford. It is mostly an aesthetic thing rather than a functional thing. I do find that larger chunks of mulch tend to be easier for tender or small plants to push through. Cedar can have a growth reduction habit if you are using western red cedar mulch or have worked it into the soil due to chemicals the cedar contains. And no, mulch does not reduce the nitrogen content of the soil unless you work it in.
Mulch will also reduce the self-seeding of plants. The mulch effectively suppresses these as well as the weeds. So, if you have aquilegia or other short-lived plants that require self sowing to survive, you can say goodbye to them after a few years. The only mulch that actually encouraged these types of plants is a stone mulch - something on the size of pea-gravel (approx 1/2 inch) and you'll find self-sowers can become weeds.
In The Old Days
In the old farm gardens, I moved all those plants into a rock garden area and pea graveled the rock garden. They thrived up there (so did the weeds) and the regular perennials did well under the straw mulch I used (straw being cheap and locally available). Our formal front yard gardens were under a larger pine chunk bark that effectively reduced weeds.
And finally, I guess if I was in your shoes, I’d tend to experiment a little bit with the mulch. I’d mulch those plants that were herbaceous and didn’t require self sowing as an experiment. I’d keep the mulch to one to two inches deep (on sandy soils, I’d go three to four inches deep) and I’d see if the plants liked it.
Mulch Decomposes
You will find that as the mulch decomposes (particularly if you use a straw based or other rapidly decomposing mulch) the top layer of soil will also change to a more organic soil rather than a clay soil. One of the reasons I used straw on sandy soils was to increase the organic matter and increase the fertility of those soils. You’ll find the same thing will happen on your clay based soil.
And if you don’t mulch. Well let me paraphrase Santa Claus. “ho-ho-ho”
Doug
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