weedy compost

[Janet Macunovich 32]

Recently we were approached regarding compost as a weed source. L.S. wrote:

I have not been pleased with the compost we have been gifted at my community garden plot. Last season after working the new compost into my plot, it rained for two days... went to the garden and my plot was covered in weeds. It took four hours to pull them out! Can I buy 100% organic compost at the nursery and have better luck? I have been gardening for three years and really enjoy it but I am not an expert! I also added worm casings to the mix.

 

We replied:

The trouble may not be with the compost but that you worked it in. Your own plot's soil, any soil, has a prodigious seed bank in it, much of it suppressed by seed depth. (As we keep a bed clean over years and more organic matter builds on top, the original weed seeds may be buried deeper, but they don't die for many years.)

 

If the compost you got was new and clean ("new" = not old/stockpiled for weeks in a place that doesn't move much compost and where weed seeds could blow onto it; and "clean" = well made, as from a large composting facility where the heat of the decomposition process is great enough to kill weed seeds) then used as a top/mulch layer, it won't create a weed problem. But if you mix it in your original soil ends up at least partially on top and those bits are surrounded by moist compost. It's a perfect seed bed.

 

Try just adding it as a mulch, then moving aside just enough of it to plant each seed or pot. Let the worms and grubs, your weeding, and fall clean-up mix it in gradually.

 

If you must mix it in, perhaps because you're employing it to keep broken-up compacted soil from falling back into its former dense shape, then fork in the compost and afterward cover the area with clean mulch.

 

To others: Any more ideas out there?