Using conifers as mulch?

We live in a suburban lot, and the increasingly dry summers has motivated us to get mulching.

We've used straw so far, and even though we've only got a sprinkling we can see how the plants that have been mulched have done so much better than those that haven't.

We've got a number of conifers (leylandi for example) that died over the past few years - foliage has turned brown, and almost all of it has dropped off.

We've got someone coming tomorrow to cut them down and shred them up, and I'm wondering if there would be any problems with using what's going to be left as mulch.

I guess my concern is the sap, but maybe one of the more knowledgeable Permies community could give me some guidance.

Thanks in advance!

Martin

Conifers are known to acidify the soil as they break down. They often do so to the extent that it is difficult for other plants to survive - the understorey of a coniferous woodland is much less diverse than that of a broadleaf woodland, particularly when the conifers are non-natives such as the sitka spruce plantations here in the UK.

Leylandii also has a very bad reputation as it takes an incredibly long time to break down. There is also concern that it is allelopathic - it releases compounds into the soil to kill off other plants. There is a study here about using it for mulch and how detrimental it was to seedling germination. This might be a benefit if you are mulching established plants and want to prevent weed growth but I suspect, in most circumstances, it will do more harm than good. You could consider mulching with a non allelopathic material, such as woodchip, then topdressing the mulch with leylandii to prevent weed seeds from germinating. I wouldn't try this with a favourite plant though.

My folks have a long, tall leylandii hedge and getting rid of the trimmings is always a bit of a battle for them. They have a separate compost heap for it and I think, sadly, some of it is burnt. It does, interestingly, have a beautiful wood.

what’s getting mulched? there’s likely a brief period where using conifer will slightly acidify the soil that it’s on, but that’s fine for many things.

Given the concerns addressed by the commenters above, I'd suggest piling them out of the way if you have the space, and inoculating with compatible mushrooms. This will accelerate the breakdown of the allelopathic factors, and possibly mitigate some of the acidification tendency as well.

I've used mulch made from various Cupressus species and so far haven't had any ill effects. But it's been in combination with other materials and that probably had something to do with it. If you're growing blueberries or other woodland plants, then that would be an obvious place to put some.

I think the assertion that conifer foliage acidifies soil has been debunked.
As to the allopathic properties of  this particular plant, unless you are mulching  seeds or seedlings it might prove to be useful by preventing uninvited plants from growing.

I had just read a paper on the alleopathic properties of some plants reducing the need for chemical herbicides. I agree with William the use of brown conifer needles increasing acidity appears to have been disproved.

We have been using pine and fir wood/bark/needle mulch for 5 years and I have seen no issues with resulting growth unless it's so deep that no sun gets to the soil. We used lots of wood chips building our garden beds. We had good growth the same year we put wood chips in the hugel beds with pine and fir logs. Now the chips have broken down into soil. So I haven't seen any sign that douglas fir, ponderosa pine, and lodgepole pine are an issue. Not sure about your particular type of conifer.

I read a great deal about using conifers for mulch and after doing so I "took a chance" and used them for mulch in a large portion of my garden.  It worked out so well I did it year after year.  My home soil testing didn't detect a change in acidity.  My vegetables loved the mulch to the degree that I made it a habit in my garden.  I've always been one to test and experiment with regard to what I read about in gardening forums.  So often I've been rewarded with results that challenge what's being repeated on various forums.  I'm just chiming in to let you know about my experience but by all means make your own decisions independent of my response.  

Good luck with whatever you decide.

Earlier this year we cut down a juniper tree that was a host for cedar apple rust.  I had some of the same concerns so used it to mulch the garden paths.  It was very aromatic and the crab apples are looking pretty healthy so think we've eliminated the fungal spread and I have a pretty weed-free path in my garden.  In a year or so I'll scoop the broken down mulch from the paths into my beds and start the process over.

Interesting to learn that the acidification is a myth. The soil beneath conifer plantations here is certainly very acidic but perhaps there is a different method of action at work.

Edit: I've just looked this up and apparently this might also be a myth. My head is being blown.

I'm loving the collective realization. I was guilty of thinking conifer = acid as well. Last year I got 20 yards of pine mulch delivered and I thought I had screwed up. I bit the bullet, said it was now or never, and I spread it thick EVERYWHERE. I tell you what, I was amazed at the results and now an arborist friend of mine will deliver all I need. Maybe we shouldn't let everyone in on the secret or our endless supply of chips might be taken away... ohh well!

I have a fantasy of a parcel planted with Christmas trees with a Chickshaw of chickens roaming the place.
The combination of needles and bird poop could be amazing.
Combined with the "stump culture" style of harvest, plus some nitrogen fixing understory plants and you'd have a pretty regenative   setup.

Conifers are indeed quite rot-resistant overall, especially when dealing with the heartwood of the species. If the main goal is the decomposition of your mulch for organic material and soil enrichment you may want to choose a different species. However, many people choose cedar, hemlock or, other conifer mulches specifically because they are resistant to decay and, often, aromatic as a secondary means to prevent certain pests. That being said, these are often wood chips from the heartwood and it is used in an ornamental capacity.

I have no personal experience using Leyland Cypress as a mulch, but as far as I am aware it is not a known allelopath according to the USDA Plants Database. Coniferous needle litter does differ in properties as opposed to broadleaf litter but I don't believe this poses a problem. If you are worried about it, you could always dilute the conifer mulch with the straw you mentioned and observe the effects on your land/plants first.

That being said, I have also observed the relative sparsity of the understory of a coniferous forest. I had always assumed it was the allelopathic tendencies of certain conifers that caused this but I have begun to believe the primary cause is the density of the forest. Specifically, the dense forest cover provided by the canopies. Combined with most conifers' preference for acidic soil and year-round coverage, it may be too difficult for many plants to survive. I'm sure there is also an interplay of moisture as well.

I hope it goes well for your plants, mulching is a great choice!
Hope this helps,

Eric S.

Thanks for all the input - so much to consider for a newbie like myself.

So, the trees are down and what we could shred has been.

We decided to use what we have (significantly less than we expected) to mulch an area that is currently overrun with weeds where we want to plant blueberries in the future but time (and finances) mean we can't do anything just yet.

Hopefully, it'll keep the area clear and we'll rake it up and reuse what's left elsewhere in the garden later on.

Thanks again - such an amazing community.

Martin

Seems like there’s a lot of competition for sunlight even in a deciduous forest. With evergreens, fuhgeddaboudit, the forest floor is even darker and there’s a thick, opaque canopy year-round. Maybe evergreens take over in succession because they grow very tall, skinny and closely-spaced, and the year-round foliage gathers light even in the shoulder-seasons.  Also if leaves are shed every second year instead of every year, nutrient cycling may be half. That would be my guess as to why there’s less plant diversity.

Was gonna suggest using it around blueberries but you already intuited that, well done! According to Michael Phillips’ The Holistic Orchard, they need only a very narrow band of acidic soil to access adequate nitrogen in the form they need it. If it has any acidifying effect, conifer mulch would only do so in a small surface strip of the soil.  However I think from observation and reading that the conifer mulch concern is vastly overstated, with the exception of redwood and cedar (cypress might be up there too). These woods are not just acidic but also contain far more complex tannins (which are antimicrobial and preservative) than pine and fir. Still, blueberries thrive adjacent to these trees, which do most of their acidifying of the soil through root exudates not needle drop. Rhodies and Azaleas also thrive there.

I don't know if it really works, but I toss dumpster citrus into my blueberry barrels to contribute nutrients and push down ph.
They also seem to like pee, so don't hold back ! 😏

I exclusively use confiers (juniper, jeffrey, lodgepole, etc) for my mulch because I'm in a forest so that's the bulk of what I have.

I'm glad the "acidification" myth was blown because it's really just now true. What I have *have* found to be true though is that pine-oil, or whatever that strong pine smell is from fresh cut things is really anti-microbial. So you should let the mulch sit for a bit (6 - 12 months) before you use it, if it's going to be really close to plans. Maybe toss some coffee grounds and other nitrogen sources into it as well to help break it down a bit. There's a lot of gray area between old mulch and compost.