Hay Under Tarp = Mold

Lesson learned!  I couldn’t fit all the hay bales inside last Spring so I stored some under a lean-to last Spring, and covered it with a tarp to keep it “dry” as the wind blows rain sideways at times. I did not realize the tarp would “sweat” and thus mold the hay.

Anyway, lesson learned, and I have a million uses for moldy hay, and I have plenty of good hay, but thought this might save someone an expensive lesson with hay they were counting on to feed.

Anyone have experience with storing hay outside without it molding?  Should I have used a different type of tarp?

How deep does the mold go?

It does not look that bad to me.

I store my round bales outside, so I just peel off the first layer or two and the hay is fine down underneath. That is the great thing about round bales, they shed water so they do not have to be kept under cover.

Hey Artie is looks like your hay is sitting on pallets. Do you have any more pallets that could be placed on top of a stack of bales for an air gap and then drape the tarp over the pallets?

Hi James, yes, it is sitting on pallets, and yes, I had the exact same thought when I pulled the tarp off! Do you think that would keep the tarp from sweating, or just create some airflow so it would dry in between sweats?  I was surprised the tarps sweat that much, although given the heat and humidity over 1.5 summers I guess I should have foreseen that and used that hay first.

Travis, if it were for cattle or sheep I wouldn’t worry too much, and peel off the black stuff. But, it is square bales for horses, and while some say they won’t eat bad hay, the risk of colic is high enough that I don’t want to take chances. I will spread it over some bare ground to get some roots in the dirt.

Artie Scott wrote:Hi James, yes, it is sitting on pallets, and yes, I had the exact same thought when I pulled the tarp off! Do you think that would keep the tarp from sweating, or just create some airflow so it would dry in between sweats?  

I don't necessarily think it will keep the tarp from sweating, but I think the air gap will allow things to dry out and prevent mold growing conditions from forming if one end of the pallets on top can be left open to vent and breathe.

If you put the top pallets at a slight angle, then tarp, the sweat will run down the slope and drip off one area. Kind of an inverse roof! :)

Good idea, thanks Pearl!

The stuff they wrap houses in (like Tyvek) is a breathable membrane. Not sure how well it stands up to wind stress and abrasion, but it's a possible alternative to building a temporary structure over your hay using wire mesh and poly.

I've been around hay yards where stacks get tarped for winter storage. Water can get through sometimes if allowed to pool. Some kind of tenting on top, usually a single row of bales, and having a tightly roped tarp does the job. But even with ideal tarping there can be mold spots in a stack from the hay itself or pockets where humidity gets trapped.
It seems that mold needs edge. A very tight stack of dry bales in a dry barn can last 5-10 years. Air gaps and any amount of moisture invite mold, but if you know it won't stay dry, air gaps like pallets on top or below an outdoor stack do help it dry out and not go bad.

I don't think tyvek would work given how breathable it is for rained on half constructed buildings, but I haven't seen what it would do on a hay pile.

Oh no! it's not just me.
I just built a small "hay closet" for the rabbit hay to protect it from rain a few weeks ago as an alternative to just putting the bales in trash bags. I just pulled out the first flake to use (after a few weeks of rainy weather) and my bale is all moldy. Sigh. I have two rabbits and can only get a whole bale of alfalfa at a time (and I pay $2.50 per kg. so it's a tragedy when I have to use a 22 kg bale as mulch), and I'm having a heck of a time storing it without mold.
I may have to try putting the bale in a trash bag (or a tarp) inside the closet. It seems like the moisture seeped through the wood into the back of the closet structure.

Alfalfa hay has a higher moisture content than grass hay. The best method I've found for storing alfalfa hay is to break the bale and use "stickers" (2" x2" sticks) to keep some air separation between the restacked flakes.

When I was riding horses in California, the stables I used had fans in the hay loft part of the barn and that was where they stored the alfalfa hay bales, these were also stickered but they used pieces of 4x4 (left overs from a barn construction).

Redhawk

Hi, I have that issue this year.. but did not have it last year. Lucky I just caught it and am peeling the wet, drying the tarp before the next rain in a couple of days. Trying to figure out what to place on hay under the tarp to breath it better.
A note people may be interested in. I stopped using pallets (as they disintegrate and can hurt your equipment wheels and are a mess to clean up with splinters and nails.. I have been collecting big truck tires and smaller ones for roll support and placing the rounds on them. It has been awesome.. easy to move and reposition and last forever. except now the tarped top ones are molding. Against the tarp.