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Have You Heard the One About Sour Mulch?

May 30, 2012

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I rely on a lovely composted wood mulch made here on Long Island. It’s a rich natural dark brown that looks & smells perfectly earthy. And it bestows all its mulchy goodness — retaining water, keeping weeds at bay, and breaking down over time, contributing welcome organics that improve the soil.

About 10 days ago I planted a brand new curvy shaped bed that I’d started prepping last year by digging in some compost in the fall.

It’s a sunny spot, so I put in 3 showy echinacea, 4 green leafed lambs ear, and 3 geranium Roxanne. I planted them using a mix of more compost and a little left over standard potting soil, the later being a non traditional ingredient in garden beds, but one which I’ve added to beds for years with excellent results.

They settled in nicely, and were sprouting beautiful buds. Then yesterday, I checked in on them and they’d been struck by SOMETHING. They were near death.

I gave them lots of water having no clue if it would help. But I only had a few minutes free before I needed to catch a bus to the city so a quick shot in the dark something — like water — would have to do.

Once I settled in for the bus ride I googled and discovered the likely culprit: sour mulch.

Aside from its slightly more pungent but still mulchy aroma, nothing seemed off about the batch. That’s what’s tricky — it can be hard to detect until its too late.

Put simply, sour mulch occurs when insufficient rotation of the mulch material leads to pockets of excessive decomposition, which in turn create compounds that are toxic to plants. Even if the material is later rotated and normal decomposition resumes, the toxins may still be present.

In this case, I’d applied the apparently sour mulch less than 24 hours before I discovered the unintended consequences. Not very long in gardening terms, but clearly long enough.

Once plant die back is observed, they say the best thing to do is heavily water the area to dilute the offending toxins and hopefully allow the plants to refresh and recover.

So that’s what I’ll continue to do, along with hoping for the best.

And of course, I’ll be tossing what’s left over from that toxic bag of what I’d thought was mulchy goodness.

UPDATE 6/2/12:
Excessive watering seems to have worked! The plants are reviving!

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From → Gardening, Mulch

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