Ask a Question forum: Leaves under pine straw mulch?

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Eastern Massachusetts (Zone 5b)
Apr 29, 2017 11:42 AM CST
Any wisdom on whether leaves under pine straw is a decent mulch?
I already did a big area that way this morning, but I'm worried it might keep too much air and rain from reaching the soil. Leaves sometimes mat into a surprisingly effective barrier.

I like the look of pine straw as a mulch. But I'm not going to buy it, and I did a worse than typical job of gathering it last fall and my bags of dry pine straw saved in the porch over the winter are nearly one third leaves.

This morning for about a quarter of my hostas, I pulled out all the organic debris (that insulated them all winter and they just sprouted through), then I weeded. There weren't many weeds in that section yet, but will be if I don't mulch aggressively. Then (the silly slow part) I sorted both the debris I just pulled out and a couple cubic feet of the dry stuff from last fall to get pine straw separate from leaves. I put leaves on the bare ground between hosta clumps, average 5 leaves thick. Then I put full depth pine straw between Hostas shoots in each clump and a thin layer of pine straw hiding the leaves in the rest of the area.

I expect it will block weeds better than the same total depth of just pine straw, hopefully enough that I don't need to weed that area again this year. At least so far, it looks as good as using just pine straw (a bit uneven because of the mix of pine straw that was there and wet all winter vs. pine straw from elsewhere that was dry, but that is an OK look). I think it is sheltered enough the wind won't pull off the top layer of pine straw.

What else should I be worried about, and how much should I worry about the leaves matting and forming too much barrier to air and water?
[Last edited by jsf67 - Apr 29, 2017 4:06 PM (+)]
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Name: Cindy
Hobart, IN zone 5
aka CindyMzone5
Celebrating Gardening: 2015 Plant Identifier
Apr 29, 2017 3:39 PM CST
What type of leaves? Are they shredded? I use shredded oak leaves here year-round but I don't put anything else on top. Shredding helps prevent matting.
Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize that we can't eat money. Cree proverb
Eastern Massachusetts (Zone 5b)
Apr 29, 2017 4:06 PM CST
Mixed leaves, including Oak, Maple and others.
Not shredded.
I do understand that shredding would eliminate the matting problem. But as it was, I was already putting too much labor per sq foot into the project.
Applying the leaves and pine straw while separating was at least a bit less handling than separating first. If I was going to shred, I would need to separate first.
I'm not really sure matting would be harmful here (in addition to not being sure they will mat). Rain water doesn't have too much chance to escape that area. Moderate sections of ground may stay dry due to matting, but most of the total water will get into the ground somewhere close. I think Hostas have deep enough roots that uneven wetting of the ground around them might not hurt much. Matting increases the anti-weed effectiveness.

I do appreciate your feedback anyway.

BTW, unshredded leaves both look ugly as a mulch and move more in the wind. I shredded leaves last year for the first time. After reading bad reviews of various leaf shredders, I ran over piles of leaves many times with a lawn mower. I had one good and one bad surprise in the way shredded leaves behave. In an open section of my back yard I used shredded leaves to start raising the ground level immediately down slope from a big Oak tree. Using dirt to change the grade would cut off oxygen to the critical surface roots and injure the tree. I hope shredded leaves won't do that (and worms will mix the leaves with the underlying soil raising the level without blocking oxygen). I don't know whether that all works, but the positive surprise was that shredded leaves sit there in the wind while full size leaves blow around. In my front lawn, I left a small amount (not enough to badly block sun from the grass whenever the snow didn't) of shredded leaves on top of the grass all winter, expecting that the actions of snow and rain and wind and worms would gradually pull the shredded leaves under the blades of grass. No such luck. I finally raked it all up recently so it isn't choking the grass. But the major issue is making shredded leaves is too much work.
Name: Cindy
Hobart, IN zone 5
aka CindyMzone5
Celebrating Gardening: 2015 Plant Identifier
Apr 29, 2017 5:14 PM CST
Ah. Sometimes shredding leaves requires pre-planning. We don't leave shredded leaves on the lawn. DH uses the grass catcher attachment in the fall when he's shredding leaves for the garden. The shredded leaves go into big lawn bags over winter and then are used as fresh mulch in the spring. Sometimes I cleanup last year's shredded leaves from the beds during spring cleanup and sometimes I don't. I get a lot of falling leaves on top of the mulch anyway since my yard is shaded by oaks. I used to go through 40+ bags of wood mulch a year but not anymore.
Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize that we can't eat money. Cree proverb
Eastern Massachusetts (Zone 5b)
May 5, 2017 6:32 AM CST
I rushed through other parts, just pulling the weeds that poked up though leaves and last year's mulch, rather than removing the old mulch, weeding and reorganizing the mulch to have the pine straw on top.
It looks like this now. The nearer parts are where I did the full job. So many other tasks to attack, so I guess I'll just leave it all and see whether doing it the harder way makes anything better or worse as the Hostas grow.

Thumb of 2017-05-05/jsf67/837b3d

This is also one of two photo angles I wanted to get, that are so difficult to get a decent photo, that I'm thinking of going up on the roof to get the photos. I go on the roof moderately often, for tasks like removing the clumps of wet pine needles that accumulate there. But I haven't decided whether getting better photos would be worth it (and won't know till I try whether I actually could get better photos from there).

[Last edited by jsf67 - May 5, 2017 6:38 AM (+)]
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Minnesota (Zone 3b)
May 5, 2017 11:32 AM CST
Unless you have an odd bio-climate those leaves will break down.

I put up to sixteen inches of leaves, removed from roses as winter cover, onto my potato planting area and by fall over ninety percent has broken down leaving from zero to at most an inch or so of cover.
I used to always use oak leaves which break down the slowest but even they do break down during the summer.
I have never had a problem with leaves not letting water through.
Eastern Massachusetts (Zone 5b)
May 5, 2017 12:15 PM CST
I have seen leaves act both ways and I still have no clue how to predict which way they will behave:

At one extreme, I put several inches of firmly packed wet leaves in the fall onto super hard packed dirt intertwined with tree roots and rocks, so you couldn't have dug down an inch with a shovel. After a winter under the snow, the leaves had been so mixed into the dirt below by the action of worms, you couldn't tell where the dirt/leaf boundary had originally been and after pulling some off the top (to use elsewhere) the ground around tree roots was so soft you could push under the roots with your fingers.

At the opposite extreme, I put similar piles of leaves elsewhere and the top matted into a water tight layer that shed the rain, while the wet material underneath had its moisture sucked out by the roots underneath. Several years later, removing the barely decomposed top layer of leaves revealed bone dry leaves underneath that had been permanently flattened by drying under the weight from above, but otherwise were unchanged from when they first fell.

Unfortunately, most of my leaf piles are closer to the latter behavior.

I wonder whether not buying a leaf shredder (because of reading the consistently bad reviews) was a mistake. I expect I would have used whole leaves anyway (less labor and likely better weed suppression) for the project described in this thread. But I expect shredded leaves would be a good answer for another project now: I dug a deep pit to cut a big stump away from its roots to pull it out whole. Using water a few times in the process, I was amazed at how water tight the dirt is there. Water simply won't sink in. I will be trying to plant some rooted branches of rhododendron above there after filling the hole and really want the hole filled with dirt that will absorb a lot of water, rather than keep it from ever sinking in. If I had a lot more pine straw, mixing that with dirt makes an absorbent soil. But I really like pine straw as mulch and barely have enough. Whole leaves mixed with dirt does not make an absorbent soil. I think shredded leaves mixed with dirt would. But shredding that much with a lawn mower would be too big a task.
Minnesota (Zone 3b)
May 5, 2017 12:54 PM CST
Packed leaves can act like cardboard.
The only time I find this is when I put leaves in a bin and walk on them to pack them down.
Sometimes then I will have to take a fork and turn over the top six to eight inches as they have become water shedding and as the leaf pile seems to drops on the outside leaving a high middle, the water mostly just rolls off, leaving the center fairly dry.
I always rough up my leaves now to that does not happen and I found out the leaves that wet easily like Maple and Mulberry will form a hard pack barrier if left to do so, whereas Oak will not.

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