Of Oak Leaves and the Timing of Mulch

Q. Stan in Brookline Station Missouri writes: "Are shredded oak leaves suitable for mulching raised bed veggie plots? The mulch I laid in the Fall contains oak leaves as part of a mixed leaf mulch. Should I remove the mulch before Spring planting? (I shredded them with my lawn mower.) If oak leaves are unhelpful, can I do anything to remedy any damage once the mulch is removed?"

A. I have been answering this 'oak leaf question' off the cuff for close to thirty years. One of my most popular talks is about making compost from shredded fall leaves, and during the Q & A afterwards someone will invariably ask if shredded oak leaves are OK to use in composting and/or as a leaf mulch. My response has always been "why shouldn't they be?" and then I'll explain that black walnut leaves contain a substance called juglone that can be deadly to other plants, especially tomatoes, even after being turned into compost; but that oak leaves are well...just oak leaves.

But still the question persists; and I can't remember ever actually looking it up. (That would be like reading the manual before you assembled the gas grill; then you wouldn't have all those nifty parts left over!) So I went online and read a LOT of articles by people and professionals also wondering why oak leaves get such a bad rap. The consensus: Yes, they are often the last leaves to fall--especially from 'live oaks', who wait until the spring--and yes, they are a little tougher and harder to shred than say, maple leaves. But there's nothing wrong with them.

A web site called "The Spruce" summed it up perfectly. And I quote: "Oak leaves seem to be surrounded by myth and misinformation when it comes to their role in mulch. While it is true that they seem to take forever to fall from the tree, and the leaves themselves are rigid and tough to mulch, the mulched oak leaf is not acidic. A Michigan State study indicates that there was no change in soil pH after six seasons of mulching oak leaves into a lawn."

So there.

No--seriously. If anything, you should tell your neighbors that oak leaves are acidic, toxic and bad for your digestive system and fingernails, but that you--as a good Christian person with the correct equipment--will take their oak leaves and dispose of them properly and responsibly. Then shred them into your compost bins and bring me any leftovers. Heck, even black walnut 'leaves'--if you can call those feathery little pieces of nothing "leaves"--are okay if they make up only a small portion of the mix.

Now: Shredded leaves as a garden mulch and the timing thereof.

Shred your leaves when they fall and as soon as you can. I was able to shred a good number of my leaves last Fall, because, luckily, I started as soon as they began hitting the ground. Then we got ice, snow, freezing rain, sleet, boils and frogs and the shredders had to come inside. (I spent the last couple of weeks making sure the leaves we didn't get up last year were gently raked or pulled off the tops of the areas where Spring bulbs emerge.)

Side note: (Actually the most important note): Yes, the leaves must be shredded for mulching and compost making. Just because you don't feel like doing it will not change the physical reality that shredded leaves become compost quickly and make a great mulch, while whole leaves mat down like a tarp, take years to compost and make as good a mulch as parking a '57 Chevy overtop of your tomatoes.

All electric leaf blowers come with a reverse setting and a collection bag. So instead of blowing your leaves back and forth onto the neighbor's driveway until one of you finally gives up and rakes them, you suck them up and shred them while standing. No bending.

Garden rule #1: Bending is for chumps! If you are bending, you are doing it wrong.

And now back to our regularly scheduled program.

Shredded leaves make a great protection for the soil in raised beds over the winter. They prevent weed seeds from settling in and limit the amount of soil heaving from repeated cycles of freezing and thawing. You got lots of leaves? Mulch all your beds with shredded leaves and then empty all the rest into the biggest wire bin you can fill. Add nothing else. Come Spring, the bottom of the pile will be finished compost of exceptional quality and the top and sides will still be shredded leaves, which I just read somewhere make an exceptional mulch.

When Spring does arrive, however, it would behoove you to temporarily rake or hoe that mulch offa your raised beds a week or two before you intend to plant anything in them. This will allow the sun to strike your soil directly and warm it up much faster.

Then plant and re-mulch. Tomatoes should only be mulched with finished, yard-waste shredded-leaf compost to help prevent the diseases to which these gateway drugs to gardening are so prone. Same with roses. Actually double with roses.

Pretty much everything else in your garden and landscape can be mulched--and should be mulched--with shredded leaves. A two inch mulch of shredded leaves prevents weeds; and earthworms will move in underneath the leaf litter and turn your lousy clay into something closer to soil.