What’s the Best Mulch?

If done correctly, most fruit and vegetable plants are their own best mulch during the growing season—spaced perfectly for plants to not only have plenty of room to meet their full potential but also shade and protect the soil with their barely-touching foilage. As an additional early help to nascent foliage or for widely spaced or sparser-leaved plants, straw is the best applied mulch for several reasons. Other mulches have their places, but leaves and hay tend to mat and smother; grass clippings are best left on the lawn; and wood chips make a great mulch for paths but pull too much nitrogen from a planting bed. For more on the pros and cons of each of these, check out “What’s the Best Mulch?”.

Straw versus Hay

The terms straw and hay are often used interchangeably by those unfamiliar with their vastly different vegetation sources and ultimate uses on a farm. Still, it’s helpful for gardeners to know the difference because straw is (usually) the much better choice for mulching garden beds for several reasons.

But what’s the actual difference between straw and hay? Why does it matter? Why is straw the best mulch for vegetable garden plants? And how do you know if you’re getting straw instead of hay?

What is Straw?

Straw—the hollow stalks of cereal grasses like oats, wheat, barley, rye, and sorghum—is a byproduct of grain production. It (and some chaff) is what’s left over after the grain is threshed from the cut plants during harvest. Because many farmers grew oats for their livestock, especially their horses, oat straw was much more common in decades past. It’s somewhat regional, but, as tractors first replaced horses and, more recently, as more and more farms grow crops only and have no livestock, oats straw is now hard to find in most places. Wheat straw is now the most common straw throughout most of the U.S. To show how dominant wheat is in comparison, in 2022, oats were planted on 2,581,000 acres in the United States compared to 45,738,000 acres planted in wheat.

What is 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. Red Clover is another common hay crop in many areas.

Why It Matters

Straw and hay are produced for very different reasons and in very different ways.

Making Straw

The grain crops that give us straw are left in the field until they fully mature and naturally die and dry before they are harvested. This allows the grain to be closer to its ideal moisture content for storage, saving money on massive drying equipment. As the plants complete their lifecycle and start to dry, they lose their green color and become the varying shades of rusty 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 stalks. The remaining stalks (the straw) and chaff (the remaining parts of the seed head) are spat out the back and then baled for use as bedding, mulch, etc.

Making Hay

Making hay is vastly different. The timothy and other grasses and alfalfa, red clover, and other legumes are mowed several times a season—whenever they reach the proper height and stage of development—when the plants are still alive and green. After mowing, the crop is left to dry in the field for several days and is tedded as needed to flip and fluff it so it dries evenly. 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.

Why It Matters on a Farm: Ultimate Uses

Because hay crops are mowed when they’re green and at their nutritional peak, they retain a much higher nutritional quality as feed for livestock. Alfalfa, for example, is mowed at very specific times in its growth cycle to attain very different nutritional qualities depending on its specific uses as forage.

Straw is the opposite. Not only is it from grains—and not crops specifically grown for nutritional quality as forage—but, because the straw stalks are dry when they’re cut, they’ve lost most of what little nutritional quality they would have had and so have very little forage value for livestock, if any at all. Instead, straw makes great bedding for animals for the same reason it makes great mulch. But why does it make a better mulch?

Why Straw Is a Superior Mulch

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.

1. 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.

2. 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.

3. 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 mat together, like leaves and hay, have several downsides. First, they impede air movement into and out of pores in the soil—movement that is imperative for plant and soil health. Further, 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 our precious young seedlings for the same reasons they smother persistent perennial weeds but even more thoroughly than they smother the weeds. Therefore, gardeners with persistent perennial weed problems are better served solving them in other ways (e.g. pulling, digging, etc.) and using less matted mulches in their gardens that discourage weeds without smothering garden plants. Straw is excellent at this.

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 rigidity in straw’s straight stalks allows it to hold this loft much longer.

4. 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 planted with a cover crop in the offseason to keep weeds from taking over and can’t be regularly cultivated to kill emerging weeds, making it much more difficult to control the annual and perennial weeds that 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.

If hay weren’t usually full of weed seeds, it’d make an excellent, highly nutritious, soil-building mulch on older plants.

One Big Caveat

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.

And an Easy Solution

I use it as an advantage. I weed the tiny wheat plants out, using them as a minor but helpful addition to the mulch, and I plan for the sprouted wheat as an advantageous additional mix in my cover crops.

Plus, if mulch thickly, as one does for garlic and shallots and can do on large brassicas, very few wheat seeds actually sprout through the mulch, and those that sprout in it are easily “massaged” (and killed) back into the mulch. 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. Easy-peasy.

How to Tell the Difference between Straw and Hay

1. Color

A person can usually tell straw and hay apart by their color.

Because it was cut while the plants were still alive and green, hay retains a faded green tone even after it’s dried and baled, just like mowed lawn grass maintains a light greenish cast for some time after it has dried. Therefore, unless it’s quite old and has been left out in the elements for so long that it’s turned almost white and then various shades of gray and brown as it decomposes, one can tell hay by its light greenish cast.

Similarly, because the stalks were dry before they were cut, straw retains its “amber waves of grain” color long after it’s baled. Therefore, unless it’s been treated with something strange (It’s crazy, but I’ve seen it.), one can tell straw by its rusty, yellowish, or khaki color.

2. Leaves

Straw doesn’t have little leaves on the stems. Some hay does.

Since it’s mostly the seed stalks and chaff, straw usually doesn’t have leaves on it. The few that remain at harvest are usually broken off during harvest. If there are some, they won’t be little broad leaves on the stems. They’ll be long, thin grass leaves.

Alfalfa, clover, and other legume hay will have little (dried up) leaves on the stems. Pure grass hay won’t have little leaves on the stems, but it should have a high percentage of flat grass leaves in it instead of mostly stalks.

3. Shape and Size

While some will have gotten bent when they were baled, straw stalks are straight and bigger.

Alfalfa and clover hay stalks are crooked, with many nodes and branches and are much thinner.

4. Hollow or Not

If all else fails, look at the end of the stalks. If they’re clearly hollow, they’re straw. If they look kind of maybe a little like they might sort of be hollow but you’re not sure, they’re hay.

More About Mulch

If you’re ready to learn more about how to use mulch in your vegetable garden, check out “The Power of Mulch,”, “What’s the Best Mulch?”, “Mulching Cool- and Warm-Season Plants”, “Mulching to Create ‘Perfect’ Soil Microclimates”, and “Speaking of Mulch: Contrasting Alliums”.