MULCH// Should You Use Hay as a Garden Mulch?

MULCH// Should You Use Hay as a Garden Mulch?

Two MULCH articles in one week? We’re laying it on thick. It’s almost Spring planting season ‘round here, which means it’s time to be thinking about mulch, if you are a mulch kind of farmer.

In continuation of our MULCH series, we are talking about each and every mulch option—at least the ones we’re aware of—where to get them, when/if to use them, the pros and cons, our personal experiences (we’d love to know yours), all the things.

And as far as mulches go, hay is a confounding one—it is prone to contain weed seeds, may have harmful residues, but—of course—a wealth of potential benefits, as well. So, does hay have a place in the garden? Some things to consider…

What is Hay?

Hay and straw are different things. Straw is simply the stalk of grains, so after wheat (or rice or rye or whatever) is harvested, farmers will often cut and bale the remaining stalks as straw. It is low in nutrients as straw is basically just carbon. But if the farmer is good, it can also be fairly low in weed seed. There is also another option, haylage, which is a specific grass grown for hay. This is expensive—but nutrient dense—stuff, usually reserved for dairy cattle fodder and hard to find. Also silage, but this is essentially the straw of corn—corn ears are harvested, then the stalks are mowed down and then treated like hay. More on straw and straw-like things at a later date, but in contrast hay is just grass that is mowed, dried in the field, raked to decrease chances of rot, piled into windrows, and balled. However, unlike straw, the “grain” of hay is not harvested so some amount of weed seed is all but guaranteed.

Chemical Residue

I once heard a (now defunct) garden supply in Nashville tell someone that all hay is organic. This, to be sure, isn’t even kind of true. Haymaking can include broadleaf herbicides or chemical fertilizers or, ahem, the one-two punch of both (get it? One-two punch? Haymaking?). The broadleaf herbicides are used for thistle, plantain, etc., while the fertilizers are used to simply replenish the soil after years of not adding any above ground carbon. Obviously, this may be a concern for growers who are hoping to remain organic, but even if that’s not your concern, hay with herbicide residue up against broadleaf plants like tomatoes ain’t good. These chemicals will kill or significantly stunt your crop. It is imperative to know and trust your hay source. Make sure they understand it’s going in a garden, especially if it’s your livelihood, so they will be honest.

Weed Seed

Weed seed can be a serious problem with hay. A very serious one. There are zero guarantees that there is not weed seed in your hay. Consider it a given. Worse than just random weed seed, it could easily be from Johnsongrass or Bermuda or something equally invasive (though the farmer should know what’s in it). Imagine having a clean, weed-free garden only to expose it to something like bindweed and never be able to get it back under control. Actually, don’t imagine that. It’s terrifying.

There are some ways for dealing with the weed seed if hay is abundant for you and you want the benefits—some reasonable, some perhaps less so:

  • Some growers will leave the hay out for one full year to be fully saturated and partially decomposed. This will help germinate or eliminate some or all of the weed seed. Note that the seeds may not all be fully dealt with this way and that dealing with the hay afterwards is basically the stickiest, heaviest, most obnoxious task imaginable… it makes me want to put this in the unreasonable category.

  • Tarping is an option. I am experimenting with this on my farm, video below, but essentially you lay your hay out, allow it to get fully saturated, spray it with a compost tea (optional) and cover it with a tarp for no less than one good hot month. More would be better.

  • One could also run the hay through a chipper/shredder and have a fan “winnow” out the seed. This would take forever, but it may be effective and perhaps—with a big enough shredder and a big ass fan—could be efficient. Please take video if you try this and send it to me at notillgrowers at gmail dot com. I would love to see it in action.

  • I came across one idea, solarizing the bales. Essentially, you wrap the bales in clean plastic and set them in the sun for a few days. Where you would get that much plastics (besides a used high-tunnel/greenhouse) I have no idea—individual garbage bags would be a mess. But, there is potential here. Perhaps, instead of tarping, solarize the hay while it’s down on a hot few days. Of course, this idea would need some testing. I would also probe the bales to make sure they get up to 120 Fahrenheit.

  • Last, mulch and mulch and mulch some more. The approach has been used successfully before (check out this NOFA talk with Liz Josep, and if you know Liz, tell her we’d love to talk with her). It may help prevent a grass takeover, though—arguably—the advantages could be outweighed by the labor and sheer amount of mulch. I might also argue that I’ve been wrong before, someone do the math.

Price advantage?

Compared to compost as a mulch, hay can be pretty cheap, especially if it’s not feed quality. We have received square bales for as low as $1 and as high as $4. You get the better price if you pick it up in the summer when it is abundant. Winter hay is always more expensive. I find it takes about 7 to 10 bales to cover one 100 ft bed enough for one season (though it may be fully broken down by the Fall in long growing seasons, which can be good for fall seeding). In contrast, I feel it takes at least 1 to 1.5 yards of compost to cover the same bed. So, even at full price hay would be $40 a bed versus compost which can run $30 a yard at $45 per bed. And $15 more per bed really adds up when you’re talking 100 beds or so.

Labor Advantage?

Assuming you’re not using some sort of fancy (and kinda dangerous looking) hay-spreading implement, fresh hay is relatively easy to spread—relative, that is, to filling up wheel barrows of compost, wheeling them out to the beds, dumping them, and spreading it with a rake. That said, you cannot seed directly into hay so you would have to pull it back and expose those weed seeds you’re attempting to mulch, or let it break down fully first. That is absolutely something to consider—no direct-seeding into fresh hay mulch. Also consider there is no harm in hybridizing mulch systems.

Nutrient Advantage?

Remember, the goal of hay is to cut the grass while it is still high in nutrients to give later to livestock when the grass is dormant. I can’t site a good study study on it, but at least versus straw, which is mostly just carbon, good hay is full of protein and would arguably make a better food for the garden. If you know of a good study, or reference in a book, I’d love to read it.

So, Should You Use it?

It is hard to pass up a great resource like hay, and for that reason we are experimenting with it on our farm to see if we can’t work it into the system. However, you have to have a plan in place for managing the weed seeds. That is going to be your biggest obstacle. Your second obstacle is going to be direct-seeding. Seeding is borderline impossible in hay unless you pull it aside.

Oh, Soil Temperature & Moisture

Hay keeps your soil cooler and wetter. If it’s the middle of the summer? Great. Spring? Maybe not so much… unless you are living somewhere that is perpetually hot and dry (Southwest-ish, in the US). The moisture and temperature element is something to consider, and also why we usually recommend a hybrid system, maybe even a sort of lasagna option Jared Smith described in his episode—some mulch, some compost, all good soil things.

Is it worth it?

I think hay can work for certain growers or certain crops on a commercial scale under the right management. I do not think hay is a great option for all growers in all areas. Have a plan in place for dealing with potential weeds before you put it down. Maybe even a back-up plan, as well.

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