What is the difference between straw and hay? I am always surprised at all of the misinformation that is spread whenever discussions start about using straw or hay in the garden. Which one has more weeds? Do they improve soil? Are lingering herbicides a problem? Should either be used in the garden?
The answers to these questions are quite simple if you first eliminate the myths and that is what I’m going to do in this post.
What Is Hay?
Hay is the harvested part of one or more plants and can include grasses and legumes. In some cases the crop is cut several times in a season in which case it usually does not include the seeds. The crop can also be allowed to mature before harvesting and then it probably includes seeds from both the crop and weeds.
Since hay is harvested from fresh green plants it is usually more nutritious than straw which is why its main use is feeding animals. Its higher nutritional level also makes it more expensive unless it is spoiled, in which case it might be free.
Hay is made from green plant material and the actual species in it will match the intended use, the local soil conditions and the local environment. Hay is site specific.
The above picture is actually hay. It tends to look like straw once it is dry.
What Is Straw?
Straw is very useful in the garden but it is really an agricultural waste product. The farmer grows some type of grain which is harvested at maturity. The remaining stem is then cut and baled to make straw. The plants are quite dry by the time the grain is harvested and at this stage of growth the plant has used up most of its nutrients to form the grain (the seeds) resulting in a low nutrient stem.
Myth #1: Straw Is Made From Wheat
Straw can be made from any plant where the top part, usually the seeds, is harvested. Wheat is a common source but it can also be made from barley, rye, rice, and oats. Even pea stems are used to make “pea straw”.
Straw is usually used as animal bedding, but it can be used as feed. It’s called straw because the stems are hollow.
Myth #2: Hay Is Made From Legumes
Many people think that hay is made from alfalfa and clover, both of which are legumes. Others think it is made from grass. The truth is that hay is a harvested green plant and can be made from a wide variety of plants including alfalfa, clover, Bermuda, fescue, Timothy and oats. Some people even make it from green wheat plants.
Which type of hay is best for the garden? Grass hay or pasture hay has 10.3 percent crude protein, which compares to a legume hay like early bloom alfalfa with 17.3 percent. More protein means more nitrogen, which is better for the garden. The best hay for you is the one you can get easily at a low price.
Myth #3: Straw Has More Weed Seeds Than Hay
I see his a lot but it’s usually not true. Some grains like wheat are available in Roundup ready form where the herbicide can be used to keep weeds very low. Even when Roundup is not used, fields are normally weed free before planting and the grains shade out many of the weeds. I think that most of the so-called weeds gardeners report from straw is actually sprouted wheat seed.
Hay on the other hand is not usually sprayed with a herbicide and weeds may even be encouraged. When hay is harvested several times during a season the first couple of cuts are usually free of weed seed because it is early in the season, but the last cut might have more weed seeds. If the hay is made from grasses, it can also include grass seed which gardeners see as weeds.
Both straw and hay can be free of weed seed, or they can have lots of weed seeds depending, on how they were grown. One does not necessarily have fewer weeds than the other.
If you find too many weed seeds when using either one as a mulch, you are not mulching thick enough. With enough mulch, the seeds don’t germinate.
Myth #4: Roundup On Straw Will Contaminate Soil
It is a common practice in colder climates to treat wheat, oats and edible beans with Roundup (glyphosate) about two weeks before harvest, a technique called dry-down or desiccation. This kills the plants, speeds up the drying process and makes the harvest more uniform. The procedure allows for an earlier harvest in cold, wet climates.
The unfounded fear of glyphosate has people concerned about contaminating their soil but that is not going to happen. Glyphosate has a relatively short half-life in soil and becomes deactivated when it comes in contact with soil. For more on this see my post, The Truth About Roundup.
What happens when you plant seeds the day after spraying with Roundup? Watch this and see: https://youtu.be/Vn43AeoPqxs
In North America, several major food producers are in the process of eliminating pre-harvest treatment with glyphosate, not for health reasons, but because of public pressure and the fact that treatment affects the quality of the grain.
A comment dealing with straw and hay on Facebook starts with, “So much misinformation and misunderstanding in this thread” and the goes on to say “Roundup causes gluten intolerance”!, No it doesn’t, nor does it cause celiac disease – another common myth.
Straw treated with Roundup does exist, but it poses no concern for the gardener.
Myth #5: Straw Is Always A Good Mulch
I love straw as a mulch in vegetable gardens but it is not always a good choice. The problem is that some straw is contaminated with persistent herbicides.
The first point you need to understand is that not all herbicides are a problem. Roundup is not a problem, but growth regulator (PGR) herbicides are. You have to understand every chemical based on its own properties – you can’t paint them all with one brush.
The problem herbicides are the so-called plant growth regulators (PGR) that belong to the pyridine group of compounds and include clopyralid, aminopyralid, aminocyclopyrachlor and picloram. These persistent herbicides remain on the straw and in the soil for several years and can affect plants grown in soil mulched with such straw.
These herbicides can also affect manure as explained in my post Herbicide Contaminated Compost, Straw and Organic Fertilizer.
PGR herbicides tend to affect broadleaf plants so they might be used on grass hay, but not on other types of hay.
It is incorrect to think that these herbicides will contaminate soil forever! The half-life of aminopyralid is about 35 days, which is short, but it will affect plants at very low concentrations (1 ppb), so it can be a problem for a few years.
Myth #6: Hay Is Free Of Herbicides
Hay is less likely to be sprayed with herbicides but it can be. Hay growers may spray to kill broadleaf weeds, but only if it is grass hay.
Myth #7: Straw Contains No Nutrients
This seems to be a common sentiment, but it’s not true. Any plant material contains some nutrients.
An analysis of straw found 3.1% crude protein, 0.1% P and 1.2% K. The same lab found that alfalfa hay contained 18.4% crude protein, 0.2% P and 1.8% K. Hay is generally more nutritious than straw, but straw is nutritious enough for feeding to animals especially in winter when hay is in short supply.
Myth #8: Straw Bale Gardening Works Great
You can make straw bale gardening work, particularly in longer seasons. It can be a good place to garden if you have no useable ground soil, but in any other situation it has few advantages and several disadvantages. For a full review see Straw Bale Garden vs Traditional In-ground Garden – A Critical Comparison.
Hay Can Combust Spontaneously
There is some truth here but this is rarely an issue for gardeners.
Hay that is baled too wet will start decomposing and generate heat for the same reason a compost pile gets hot. If enough heat is created, the hay can spontaneously catch on fire. This is a concern when hay is stacked into larger piles and even the large round bales can get hot enough inside to burn. It is unlikely that one or two small bales, even if stacked, will generate enough heat to combust. Once hay is spread out as a mulch layer it won’t generate much heat.
Straw contains less nitrogen which results in slower decomposition and less generated heat. Large wet straw piles found in a barn can be a problem but the small bales of straw used by gardeners are unlikely to self combust. A bale that measures less than 120 F (50 C) is in no danger. They generally need to get over 160 F (70 C) before they spontaneously combust.
Myth #7: Hay Rides Are Fun
They are fun but rare. They are usually straw rides!
Straw Or Hay – Which Is Better?
Straw is a good choice for mulching the vegetable garden provided it does not contain one of the persistent herbicides. Hay will add more nutrients, but is generally more expensive. If you can get spoiled hay for a good price, grab it – there is probably nothing better for mulch.
If weeds are a problem, stack the mulch higher.