Straw vs. Hay

How to Tell the Difference between Straw and Hay and Why It Matters

People often ask about the differences between straw and hay and which is better for mulching a vegetable garden. Here’s a simple explanation of their differences and why one is better than the other for mulching vegetable gardens.

Straw

Straw is the hollow stalks left over after threshing grain from the heads of cereal grasses. It can come from oats, wheat, rye, sorghum, or any other cereal grass. Several decades ago, oat straw was more common because many farmers grew oats for their workhorses. Today, wheat straw is far more common and is typically what one finds at stores selling straw. To give an idea of how much more common wheat straw is today in the United States, in 2022, oats were planted on 2,581,000 acres, while wheat was planted on 45,738,000 acres.

The way grain crops are produced makes their straw much different than hay. To allow the grain to naturally get to a lower, ideal moisture content (or as close as possible), grain crops are left in the field until they naturally die and dry before they are harvested. As the plants die and dry, they lose their green color and become the varying shades of yellow and khaki we associate with “amber waves of grain.” When the grain is dry enough, a combine cuts the stalks close to the ground before pulling them inside to thresh the grain off the heads. The remaining straw is spat out the back—along with some remaining parts of the head—and is baled for use as bedding, mulch, etc. This “dried before cutting” quality of straw is one of the three key differences between it and hay. Because the stalks are dry when they’re cut, they’ve lost most of their nutritional quality and so have much, much less forage value for livestock, if any at all.

Hay

Hay is herbaceous plant material cut green, dried, and stored for later use as animal feed. In the northern half of the United States, alfalfa is the main crop used to make hay. In the southern half of the U.S., various grasses and mixtures of grasses and legumes other than alfalfa are common.

In contrast to straw, because the crops used to make hay are mowed when the plants are still alive and green, they retain a much higher nutritional quality as feed for livestock. Crops like alfalfa are even mowed at specific times in their growth cycle to attain the highest nutritional quality. After mowing, the crop is left to dry in the field for several days—and is raked after a day or two to flip and fluff it to aid in this process. Once it’s dry enough to be stored in bales without rotting (and possibly bursting into flames) in storage (true story), the hay is baled and stored for later use as feed for livestock. Even after it’s dried and baled, because it was cut while the plants were still alive and green, the hay retains a faded green tone, just like mowed lawn grass maintains a light greenish cast for some time after it’s cut. For this reason, a person can often tell the difference between straw and hay just by their color.

The Key Differences and Why They Matter

Other than their relative quality as animal feed, hay and straw have several other key differences that set them apart when one is deciding which to use as mulch.

Hollow Stalks Equal Excellent Insulation

Having hollow stalks—just like the drinking straws that take their name from it—gives straw another advantage: It’s a great insulator. Just like superbly insulating, hollow polar bear fur, straw traps insulating air not just between its stalks but also within them, making it a wonderful soil insulator.

Easier to Customize for Small Seeds and Seedlings

These hollow, straight, rigid stalks also make it easier to crumble and break straw into shorter pieces that make great light mulch for smaller seeds and seedlings.

Fluffy vs. Matted

Straw allows for fluffier and less matted mulch long-term. Both straw and hay are compacted when they come as bales, but, because it’s made of straight stalks, straw allows for much greater looseness and fluffiness, especially over time, which is much better for your garden soil and plants.

While they may be somewhat decent at smothering persistent perennial weeds, mulches that tend to matt together, like leaves and hay, have several downsides. They impede air movement into and out of pores in the soil—movement that is imperative for plant and soil health. This lack of breathing can also keep too much moisture on the soil’s surface, making the soil too soggy for optimal plant health. Finally, matted mulches are terrible options for garden plants that need to grow through them. They tend to smother these garden plants even more thoroughly than they smother persistent perennial weeds. Gardeners are, therefore, better served by curing persistent weed problems in another way (pulling, digging, etc.) and using less matted mulches in their gardens.

As you shake and loosen straw or hay while applying it as a mulch, the stems and pieces catch on each other and hold each other up allowing for the fluffiness you want in a garden mulch. Over time, however, both hay and straw will settle somewhat. Hay, unfortunately, is more likely to settle into a denser mat. As wind and rain push it down over time, the tiny stems and leaves, that originally caught each other while shaking the hay onto the bed as mulch, give way, and the thin, bent stems and presence of leaves allow it to settle into a fairly dense mat. Because straw is mostly straight stems, in contrast, its fluffiness comes mostly from that its stems fall on top of each other in cross-hatched patterns, and the the rigidity in straw’s straight stalks allows it to hold this loft much longer.

Number of Weed Seeds

Finally, straw contains fewer weed seeds. Both hayfields and grain fields can suffer from annual weed problems. However, cereal grain fields are replanted each year. Plus, the fields only grow grain crops for a few months. Both of these attributes make it much easier to deal with biennial and perennial weeds before and after the growing season (and in the old days, during) with cultivation and/or cover crops. By their very nature as perennial fields, hayfields, in contrast, can’t be regularly cultivated and/or planted with another crop that would smother the weeds, making it much more difficult to control the perennial weeds that can invade them. Additionally, since the prices farmers get for their grain can be significantly reduced if the grain contains too many weed seeds, grain farmers tend to be careful about minimizing the number of weeds in their fields. In contrast, while one can get certified weed-free hay, it’s much more expensive, and most local hay is understood to contain a certain amount of weed seeds.

That being said, recently, wheat straw has been filled with a greater amount of unthreshed grain (which makes one wonder about the attendant lost productivity and profits). These seeds (i.e. wheat berries) will sprout and grow wheat. Some gardeners detest straw mulch for this reason. I use it as an advantage, for example, weeding the wheat plants out and using them as more mulch or planning for the sprouted wheat as an advantageous additional mix in my cover crops. Plus, if mulched thickly, as one does for garlic and shallots and can do on large brassicas, very few wheat seeds actually sprout. Even on moderately thick mulches, for example, on peppers, the number of wheat sprouts is actually quite minimal and easy to quickly weed out, especially if you catch them early and do a little here and there. And if I ever don’t want wheat “weeds” growing in a certain spot in my garden, I just break the bale and leave the straw out to “season” (i.e. pre-sprout its seeds) on a path or a spare, bare spot in a garden bed before I spread it where I don’t want wheat sprouts.