6 Good Reasons to Use Pine Straw Mulch in the Garden
Mulch serves a lot of purposes in the garden, especially if you’re trying to grow more sustainably. A good organic mulch layer conserves moisture to keep the soil from drying out too quickly, meaning less need for watering. It keeps roots cool on hot days and provides a buffer between your plants and common soil-borne diseases. Natural mulches also feed the soil, adding nutrients as they break down over time.
Some of the more popular options are straw, shredded leaves, bark chips, and arborist’s wood chips (raw, untreaded chips). It’s a thumbs up, on any natural material that isn’t treated with dyes or rot inhibitors (you want your mulch to rot!).
Of all the mulches folks like to use, pine straw often gets left out of the discussion, or sometimes even warned against. But it’s kind of a hidden gem! Once you break down the facts, pine straw has the edge on some of the other mulch materials. It’s largely safer, when it comes to potential mulch issues, and it actually has a lot of benefits for the garden.
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Will pine straw make your soil too acidic?
The main reason gardeners are wary of using pine straw for mulch is the belief they’ll lower soil pH and affect plant health. Most vegetables need a neutral to slightly acidic pH to absorb nutrients properly. Super acidic soil can cause nutrient lockout and sad plants. Thankfully, though, the pine needles = acidic soil myth has been thoroughly debunked.
Pine trees enjoy acidic soil, and the needles themselves are indeed quite acidic, after they first drop from the tree: somewhere around 3.2 – 3.8 on the pH scale. Once they’re on the ground, though, soil microbes gradually neutralize the pH during the decomposition process. By the time those decayed remnants become part of your soil, they’re no longer acidic.
Why won’t anything grow underneath a pine tree, then? If you know, you know. Folks often assume this is due to soil acidity caused by the pine needles. The real reason: pine trees are greedy things with shallow roots (hence their tendency to topple over during storms). Most things you try to plant near or beneath them will struggle to thrive because they simply get outcompeted for water and nutrients.
In the woods, understory plants and saplings have trouble sprouting or taking root near pine trees because of that dense layer of needles blocking the light, not because of soil acidity.
Now that we’ve got that out of the way, let’s talk about six reasons you should absolutely put some pine straw on your garden.
1. It’s inexpensive (or free!) and widely available.
Pine straw is a popular budget option for landscape mulch, so it’s not hard to get your hands on in most areas. You can buy pine straw by the bale from landscaping places and home improvement stores, generally for less than $10 a bale. Locally owned businesses usually have the best price. Here, a full bale runs me $4 at our local landscaping supply place. I can mulch one of my 4 x 12 garden beds with about 2/3 a bale!
Got a pine tree, or several hundred, on your property? Then you’ve got free pine straw. Pine trees drop a lot of needles in the fall, even though they’re evergreen. We have about 3.5 acres of pine woods at our place, and we gather most of our pine straw mulch from there.
Since we have a pretty big garden, we sometimes need to supplement with purchased pine straw at certain times of the year. You don’t want to take too much at one time from forested areas, since stripping the natural mulch layer down to the dirt can cause erosion and other issues for the ecosystem there. We go through and gather the top layer from areas where the needles are thick, taking care not to expose the ground.
2. Pine straw doesn’t pose an herbicide risk.
Regular wheat straw, though one of the most popular mulches for organic and natural gardens, comes with a considerable risk. It’s one of the most common ways gardeners unknowingly introduce destructive herbicide residue into their soil.
Straw is a byproduct of grain production, usually sourced from grain farms. Once the grain is harvested, the stalks are cut, baled, and sold as straw for animal bedding and garden use. Unless you can get your straw from a certified organic farm, it’s quite likely those fields were sprayed with herbicides to control broadleaf weeds at some point during the season.
Some of the herbicides commercial farmers use dissipate soon after they’ve done their job, so they don’t pose any threat to gardens. But others, such as aminopyralid and clopyralid, have long half-lives. These can remain active and destructive in the straw long after it’s baled and sold.
Unfortunately, “persistent” herbicides are becoming more widely used in commercial farming, and way too many unsuspecting gardeners have found out about them the hard way. Once they leach into your soil from contaminated mulch, most vegetables and flowers won’t grow normally in that area for months to years.
Pine straw is harvest from woodland areas, not farmland or grain fields, so the chances of it containing herbicide residue of any kind are almost zero. It tops the list for being one of the safest mulch options you can use.
Read this post for more about how to keep persistent herbicides from finding their way into your soil: How to Protect Your Garden From Persistent Herbicides.
3. Pine straw isn’t full of weed seeds.
Another less dire problem with wheat straw mulch is the alarming number of grass seeds it may be harboring. And let me tell you, that stuff can take over a garden plot in no time.
For an example:
Last winter was a really cold one for us here in the north Georgia mountains. We had several nights with temperatures around 3 or 4 degrees Fahrenheit, with daytime highs barely breaking the teens. That doesn’t happen too often here, and when it does, it usually doesn’t end well (you’ll see folks out digging up their busted waterlines once the temps rise).
I have a frost-free spigot for my garden’s irrigation system, but I wasn’t sure how deep the ground might freeze with that level of cold. So, I plopped a few straw bales around the spigot for extra insulation so the pipe wouldn’t freeze where it runs down to our main water line. Fast forward to spring, and the forgotten bales were sprouting grass like one of those Chia pets.
Just think, all those little weeds would be in my garden if I’d used that straw for mulch. Since pine straw comes from forest floors, it contains few if any weed seeds. Sure, there might be a couple maple or oak seeds in there somewhere, but teensy trees are non-spreading and easy to pull if they happen to pop up.
4. It’s less prone to matting.
Mulch mats are a common problem with natural mulches, especially if you’re using no-till gardening methods involving heavy mulch layers. Straw pieces and leaves tend to soften and stick together as they age and get repeatedly saturated with rain. When layered thickly, they’ll sometimes fuse into a thick, impenetrable mat that can suffocate your soil and prevent water from reaching it. Obviously, that isn’t great.
Pine straw, because of its unique consistency, is a lot less prone to matting. It becomes brittle and crumbles as it ages, which means your mulch layer will remain breathable as it breaks down.
5. It lasts longer than other natural mulches.
It’s crazy how fast mulch will just…disappear, after a few months of exposure to the elements. I can put down a four-inch layer of shredded leaf litter on my garden beds in the fall, and by spring, I’ll already see bare spots poking through. Mulch needs to be at least thick enough to cover the ground completely to provide its benefits for the garden. Once it starts to wear down, you have to shore it up and add more.
We’ve found that pine straw holds up a whole lot longer than leaves and straw. We put down a fresh layer in the fall, and we don’t have to do a lot of supplemental mulching for the rest of the year. That’s because pine needles naturally decompose a lot more slowly than leaves and straw.
Pine needles are also harder for the wind to pick up, which means you don’t lose bits of mulch on blustery days. That makes them perfect for gardeners who practice no-till methods and prefer to keep their garden mulched year-round.
6. Pests don’t seem to favor pine straw mulch.
I won’t sugarcoat this, y’all. Despite its benefits for your soil and your plants, keeping your garden heavily mulched provides hiding places for pests. You may notice an increase in certain pests, such as slugs and cutworms, especially when you first begin using deep mulch layers.
Aside from squash vine borers, which are an equally huge problem with or without mulch, slugs are by far the biggest pest we deal with in our garden. They hide under the mulch during the day, then come out and feast on plants at night or whenever it rains.
Now, it’s a complete myth that slugs won’t cross pine needles. They definitely will (see below). However, when we first started mulching some of our beds with pine straw, we noticed considerably less slug damage in those beds compared to those mulched only with shredded leaves.
It appears that, at least in our garden, the slugs don’t like to nest underneath the pine straw. They’ll definitely slime across it to get to my cabbage, but I’ve seen no evidence of them hanging out and laying eggs underneath it like they do beneath leaves and straw.
Also, I can say I’ve never had cutworm damage in beds exclusively mulched with pine straw. Like slugs, cutworms also hide under mulch during the day and feed at night. This might not be the case for everybody everywhere. But it’s worth mentioning, since pine straw mulch did noticeably reduced pest activity for us.
Tips For Using Pine Straw Mulch
Here are several tricks we’ve learned for mulching with pine straw:
Put the mulch down before you plant.
I know I’ve been singing the praises of pine straw this whole time, but truthfully, it can be a little bit of a pain in the butt to work with. Because it tangles easily and doesn’t like to lay down flat at first, it’s difficult to get fresh pine straw situated around plants that are already in the ground.
Getting the mulch laid down a few weeks ahead of putting out transplants allows the pine straw to chill out and settle down some. It’ll help even more, if you’ve got a few rains in the forecast between mulching and planting. Once the pine straw has lost some of its stiffness, you can easily pull open a little hole for each plant to go in.
What about direct sowing?
Some things, like garlic, can push through the pine straw when they sprout without trouble. For most crops you want to direct sow, though, you’ll need to pull the mulch aside, sow the seeds, and wait until the plants are up a little ways to push it back in place.
Use pine straw as a buffer to secure other natural mulches.
While it’s a boon that pine straw takes forever to rot, it’s also a slight drawback, when you’re mulching to build soil nutrients. For example, if you’re using the Back to Eden no-till method.
Since pine needles take longer to decompose, they add organic matter to the soil a lot more slowly than other mulches. For that reason, I like to put down a layer of leaf litter, followed by pine straw. The pine straw holds those leaves in place as they break down and feed my soil, preventing them from blowing around in the wind. Keep in mind this might cancel out any anti-pest benefits pine needles have, since those pests like the leaf layer!
Keep a finer mulch on hand for small seedlings.
If you’re planting smaller transplants, especially short and stocky ones like cucumbers or cabbages, it can be hard to get the mulch close enough without kind of…burying the seedling in pine needles. Ideally, the mulch should come within an inch or two of the stem, in order to keep the soil insulated and moist. I remedy this problem by having some shredded leaves on hand to fill in the gaps, until the seedlings get big enough for a heavier mulch layer.
At the end of the day, the best mulch to use for your garden is whatever natural material is cheapest and easiest for you to get. It’s good to know pine straw is a top choice, since it’s low-cost and likely available even in areas where other mulches are harder to come by. If you’ve had trouble finding a good mulch source, it might be just the thing.
