Storing Hay So It NEVER Gets Moldy


We’ve all heard about the different ways you can cover your hay stack with a tarp so it doesn’t get wet or moldy.

But have you ever heard about using commercial-size dessicant pouches to absorb moisture under your hay tarp? Thought not. Neither had I, until I met an innovative horse-owning couple, Sandy and Roger, who also owned a packaging business!

If you’re wondering what dessicant pouches are – they are the absorbent little packets manufacturers put into supplement bottles, electronics, certain packaged foods, and anything else that can be degraded by moisture. They are often made of substances like silica gel, activated charcoal, and bentonite clay. What does this have to do with keeping hay dry and non-moldy? Well, these dessicant pouches also come in large bags, that are used inside containers shipped to Asia.

cargo-dry1The dessicant bags that Sandy and Roger hang in their barn are 1500 gm Cargo Dry Paks. They come in boxes of 10 and you’ll need to use 5 paks or bags per year. If you want to buy from them in Canada at Buyer’s Packaging in Delta, BC, be sure and mention that you want to use the dessicant paks to protect your hay – they give horse people a substantial discount over regular customers!

If you want to buy from the States, you can purchase the same 1500 g Cargo Dry Paks on Amazon. The great thing about this brand (Cargo Dry Paks) is they can just be thrown in the garbage when they’re used up (natural ingredients), and they come with the tie-strings attached (so you can easily tie them to the poles – see below). Note: When price shopping for these dessicant bags, be sure to check the shipping charges – the cost of shipping is often equal to the cost of the bags, because they’re so heavy.

How To Set Up Super Dry Hay Storage

If you need to store your hay in an open field, or under a pole barn, or some other structure that is not completely enclosed, follow these instructions to create a completely enclosed, dry, protected hay storage area; using only tarps, wooden pallets, commercial-sized dessicant bags, and a few poles.

NOTE: This method works best for hay that is going to be stored for a while – not for your active hay stack that you’re pulling bales from every day. For active/temporary hay storage, see the section further down.

Step 1: Cover the area you are going to place your hay on with wooden pallets. Then cover the wooden pallets with a basic blue poly tarp that extends at least 3 feet beyond the perimeter of your hay stack, on every side (you’ll need this extra length in Step 3). The ground tarp prevents moisture from coming up from the ground and into your hay.

Step 2: Stack your bales in a pyramid/cone shape so that any water runs easily down and off. Here’s a trick my Dad figured out: Take a bunch of rectangular Lego pieces – designate 1 piece of Lego for each bale. Figure out the ground area you have and set up your lego/bales to cover the total area. Then experiment with how to build your stack of hay bales. Bring your finished Lego stack model with you when your hay arrives and show it to the guy unloading the hay – a visual is MUCH easier to understand and will save you 10 minutes of explaining!

Step 3: After your hay is stacked properly, you bring the sides of the bottom tarp up and tuck them into the lower bales, or, tie the tarp so it stays wrapped up the sides of the bales. Now you know why you need at least 3′ of extra tarp extending beyond your hay stack on all sides. If you left the bottom tarp flat on the pallets, water would eventually run from the edges of the tarp into your hay stack. I don’t have a picture of what this looks like on a big hay stack, but here’s what it looks like on a smaller stack – you can see how I’ve used bungee cords to secure the sides of the tarp up around the bales:


Step 4: Now it’s time to create a tent using a UV resistant, 100% waterproof hay tarp (see below for specs and purchasing details). You need to use a hay tarp that is large enough to cover your entire stack, loosely (you need to leave room to hang the dessicant bags – see Step 5), all the way to the ground, and then tuck in underneath your bottom layer of bales, at least a 6″ flap tucked in. The goal is to create a completely enclosed, water tight storage tent.
NOTE: You can only completely enclose a hay stack if the hay has already been off the field and left to dry out completely (usually 1 month from cutting). Otherwise, the heat still in the hay will condense, resulting in moisture trapped in your hay tarp tent, which can then cause moldy hay. If your hay is not completely dry, then only cover the top and part-way down the side of the stack, until your hay is dry.

Step 5: Set up your commercial-sized dessicant bags (1500 grams, approx. 6″x12″) inside your hay tarp tent. Sandy and Roger (mentioned above) told me they have experimented with numerous different placements and the best way is to hang each bag from a pole, spaced evenly around the stack. They use 5 bags, which last the whole year. You can see when the dessicant bags are used up, because the water starts to drip out of them. You cannot dry them out (they’ve tried!), you just need to throw them away when they’ve hit their moisture capacity.

You can erect 5 poles that come up from the ground around your hay stack, then tie the bags to the top of each pole. But that is too difficult for me (I’m no Bob the Builder), so instead I placed poles horizontally across my hay stack, 2 rows from the top. The bales on top held the poles in place with their weight. I jutted the poles out about 14″ from the side of the closest bale and tied my dessicant sacks to the end of the poles with the tie-strings. Voila! I found it easiest to buy 4′ long metal poles from Home Depot.

When I want to remove a bunch of hay from my tarped stack, I simply open up one side – by pulling the cover tarp out from where it is tucked underneath the bales, and releasing the ground tarp on that side. I remove the bales, then bring the ground tarp up over the sides again, and tuck the cover tarp back underneath the bottom bales again.

Storing Hay In An Enclosed Barn or Shed

Of course, if you have an enclosed barn or shed to store hay in, you don’t need to tarp at all – then you can just hang the dessicant bags on poles around your hay stack, or hang them from the ceiling.

If your barn is open for airflow, you can stack lower-priced “sacrifice bales” against the opening to block most of the wind/rain, but still allow for some airflow. This is what Sandy and Roger do in their barn – combined with the hanging dessicant bags, they have not had ONE moldy bale since they discovered this system of hay storage 12 years ago. And yes, they live in the super wet, super rainy Pacific Northwest (Langley, BC).

Purchasing Cheap but Good Quality Hay Tarps

In my search for the best deal on a large hay tarp that would fully cover 65 bales and tuck in underneath them, all the way round, I compared both price and quality from 4 different tarp supply companies. This is no small task as you need to write down the weight per square yard, the denier, the weave count, and the material for every tarp you compare pricing on. You also need to make sure the tarp is 100% Waterproof (not just water-resistant), UV resistant, and it is nice if it is acid resistant, tear resistant, and has arctic flexibility (although this last one is a must if you get cold winters).

It really pays to do your research as prices for exactly the same tarp could be anywhere from 30% – 50% higher, depending on which supplier’s site I was on.

And then I discovered another trick – you’re going to love this one! I was on (which had the cheapest tarps) and I discovered that tarp companies can list pretty much the same tarp, but in a different category, and charge completely different prices for it!

So I’m in the Hay Tarp section and ONE 25’x33′ foot hay tarp costs $189. Then I click over to the Gym Floor Cover section (because my daughter’s a gymnast and I got curious) and lo and behold, I can buy TWO 20’x30′ tarps for only $192. And the specs are very similar – so similar, I’ll bet I couldn’t tell the difference between them if they were lying side by side! The main difference is the hay tarp is 8.5 oz per square yard, and the gym tarp is 8 oz per square yard. Crazy hey? BUT, if you’re willing to drop to 6 oz per square yard, you can get those same TWO 20’x30′ tarps in the Poly Tarps section for only $168! And yes, you can buy them singly as well.

What SIZE Tarp Do I Need To Cover My Hay Bales?

Oh, here’s where things get difficult! Especially if you’re not a math whiz.

The easiest way to figure out what size tarp you need to get is to call your hay farmer and ask, “If I’m going to stack X bales from you, in a pyramid shape (so the rain runs off), what size tarp do I need to cover the entire stack down to the ground, with about 6″ free to tuck in all around the sides of the stack?” This is because hay farmers are usually pretty familiar with tarping hay stacks and can probably guesstimate better than you can. Then just add 2′-3′ on to each side to allow for the hanging dessicant bags (see Step 5 above).

The harder, but possibly more accurate way to determine what size tarp you need, is to get the width, depth and height measurements of your hay bales. Build your Lego model (see Step 2 above) and then use the real hay bale measurements to figure out the real size your hay stack will be. You can delegate this task to any math whiz you know and she/he will be able to figure it out.  Again, then add 2′-3′ on to each side to allow for the hanging dessicant bags (see Step 4 above). Don’t have any Lego? Oy vey, well now you’re going to have to draw your hay stack model – easiest if you print off some graph paper and make 1′ = 1 square on the paper. You may have to tape a few sheets of graph paper together, depending on how many bales you have.

Storing Hay In Use For Daily Feeding

For a hay stack you are in and out of daily to feed your horses, you do not need to use the dessicant pouches.

If your hay is in a field, or pole barn (roof only) you are going to have a hassle getting in and out of your hay stack every day, since you need to wrap it up really well to prevent rain being blown into your hay stack. You can reduce the hassle a bit by just opening one corner of the stack at a time. So when your storage does not have walls or a roof, you need to lay down pallets, then place a ground tarp over the pallets and pull it up on the sides of your bales:


Then you place another tarp over top of the bales and tie it (and weight it down if needed) to prevent the wind blowing it off:


However, if your hay is in a more enclosed barn (with some walls and a roof) then I found it works fine to put a thick tarp (like those used to cover RV/campers) right on the ground, then lay pallets on top of the tarp, then cover the pallets with another tarp, then stack your hay, and then put a third tarp to cover your hay stack:


You can either tie the top tarp firmly around the stack (to prevent the wind blowing it off) or, you can lean extra pallets against the sides – which I find easier. If you don’t want to cover your pallets with a second tarp, then you are going to have a lot of hay wastage. If you live in a damp climate, the hay that drops into the pallets will get moldy in a few months time and you will have to clean out your entire storage (and the pallets!) and start again. If your horses are eating through your hay stack within 3-4 months, this method works great.

In my research, I read many reports from people who were buying an entire winter’s worth of hay for several horses all at once – so storing a huge volume. The consensus in that case seemed to be that you put the tarp on the ground, then the pallets. But you don’t put another tarp on top of the pallets, because that will block the airflow. They said it worked better to put a bottom layer of cheap hay or straw (as the bottom layer will always get some mold), and then your good hay. And of course, cover the whole stack with another tarp over the top and sides.

One last tip: When you are stacking your hay for long-term storage, Dwain Meyer from North Dakota State University recommends this method:

“Stack bales for air circulation. Large square bales should have a 4-6” gap between bales to increase air circulation for both indoor and outdoor storage and allows for the natural hay sweating process. Place the bottom layer of small square bales on their sides so the uneven, non-stringed surface rests on the floor (if pallets are not used) to aid air circulation throughout the stack. Leave space between the bales in each row and alternate the orientation of successive layers so bales are at right angles with layers above and below. This pattern “ties” the stack together, while also keeping bales from packing together too tightly. Rows of large round bales should be separated by 3-4’ to aid air circulation.”




Storing Hay So It NEVER Gets Moldy

9 thoughts on “Storing Hay So It NEVER Gets Moldy

  • September 22, 2017 at 11:54 am

    I thought it was nice that you specifically mentioned how this advice was meant long storage. My aunt needs to invest in some hay and hasn’t been sure how to prevent it from getting moldy. I think this suggestion to use wooden pallets and tarps will work out quite nicely for her.

    • October 5, 2017 at 11:30 am

      Let us know how it goes Becca!

  • October 5, 2017 at 3:23 am

    I put up a hay stack,just to see if I remember,can you put a tarp over the tarp?will it sweat or get moldy?here it is oct hopefully it wont get hot?please reply !thanks..

    here it is:  

    • October 5, 2017 at 11:30 am

      Hi Randy, From what I know, if the hay is completely dry, then you can tarp it. BUT – what have you got in place to stop moisture coming up from the ground? If your stack is right on the earth and it freezes, that may be okay. But if you get rain/damp, then it’s going to mold from the bottom up.

      • January 28, 2020 at 1:05 am

        We live in the PNW South west Washington. Trying to store a years worth of hay has been a challenge. The only thing suggested for daily use if hay we have not done is leave space between bales. Not sure how that would work with stacking 100 bales 12 ft high. I get the idea though. I am wondering about salting the bales. Would horses be ok with that?

        • January 28, 2020 at 1:21 am

          In my experience, salt attracts water. You also couldn’t control salt intake, so if they get too much you’d have to balance the electrolytes… Well if you try it, please let us know how it goes!

  • June 8, 2018 at 1:02 pm

    I store 4×4 round bales in 24×24 3 sided pole building. I cover bottom with plastic. I then put down pallets. This year the bottom bales have shown signs of mold. I can’t figure out why. I did put 6” of limestone on bottom to allow for drainage. I also put spouting on building. Why is it molding? I thought about putting plastic on top of pallets. I would appreciate any suggestions. Thank you

    • June 8, 2018 at 5:05 pm

      Funny you should post this as I’ve just been talking to a whole bunch of people about storing round bales! The consensus seems to be that unless you are in a VERY DRY climate (like Alberta or Arizona), it’s a total crapshoot whether your bales will have mold, or not. The round bales themselves turn into ‘cookers’ with the internal temperature at the core escalating quickly if there’s any microbial activity – which is then insulated/incubated by the dense surrounding layers.

      If I were you, I would try putting plastic on top of the pallets too. And if possible, I would make your bottom layer a platform of straw (sacrifice) bales – just the normal 65 lb bales. Please let us know how it works out – the more knowledge/info we can share, the better!

  • October 13, 2020 at 9:51 pm

    It’s interesting to learn that simply using tarps can help storing hay effectively. I’m currently helping my uncle find a hay bale supplier because he has been thinking about taking care of livestock soon. I hope he would allow me to ride one of his horses someday since I’ve always been curious about what that would have been like.


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