Not as Much from Mulch as I was hoping….

(Question)

I’ve recently attempted to mulch over some parts of a back garden which I don’t wish to use this year. I turned the soil, then placed newspaper down and mulch on top. I still see weeds popping through. This amazes me in the clay-like soil which hasn’t been used in decades in west-end Toronto, near a pathway in this garden, to the laneway. It’s not as bad as a neighbour who decided to uproot his front lawn, and has bunches of grass growing all throughout the faded orange mulch of last year.
Am I just not digging deep enough to get the roots out? Or should I just tolerate some of these weeds, enjoy the parts of the garden which are planted and will soon spring peonies, roses, irises, phlox and mums? It’s just trickier to pull these up now, but I guess this can be done.
I’m about to give up and just let some “professional” use landscape fabric and mulch, since it doesn’t seem to be working.
Advice please?

(Answer)

Mulch can be either organic (wood chips, bark) or inorganic (stones, gravel, pebbles).  Presumably you are using some form of organic mulch.  One of the many benefits of applying mulch to the garden is preventing weed growth.  However, it is not likely to be 100% effective.  At best you may be able to control the number of weeds but not completely eliminate them.  Many weeds reproduce by seed while others reproduce by underground tubers or rhizomes.  With weed seeds, the concept is to block them from any sun and moisture so they will be unable to germinate.  Unfortunately, seeds blown in from neighbouring weedy areas may have reached your mulch and have taken hold.  Weeds that reproduce by underground parts can be even more difficult to eradicate.

Note: weeds are tenacious and determined to grow, whatever the conditions.

By turning the soil, you’ve attempted to remove existing weeds from the area to be mulched and by adding the newspaper you added another barrier, which is very good.  If weeds are re-growing it could be that some were left in the soil and the turning was not deep or thorough enough.  While turning the soil, it is best to remove any weed roots at that time.  Another point to consider is the depth of the mulch and the number of layers of paper applied.  The thicker the newspaper layers, the better – it has been suggested that 5-10 sheets of newspaper suppresses sprouting weed seeds and makes life more difficult for underground roots to re-sprout.  Mulch should be at least 2 inches deep and remember that organic mulch needs to be replaced from time to time, because it will decompose.   Maybe you didn’t put down enough paper layers or your mulch isn’t deep enough.

It really isn’t realistic to redo the work that’s already been done.  If weeds appear in the mulch, cut off any top growth before the plants have a chance to set seed or pull them completelty up.  Unfortunately, cutting off the top growth of non-seeding weeds, may encourage more shoots to grow so you may have to be vigilant.  You have to repeatedly cut and/or pull up the weeds until the carbohydrate reserves stored in the underground runners & roots is depleted, and the plant finally dies.  I’m sure you know about dandelions – if you don’t pull out the whole tap root, the plant will grow back!

Hopefully, you can just pull out the few offending weeds and as you suggested enjoy the planted part of your garden.

For further reading on mulch go to:

https://pubs.ext.vt.edu/426/426-724/426-724.html

https://www.nrcs.usda.gov/wps/portal/nrcs/detail/az/home/?cid=nrcs143_023585