Straw doesn’t come from a single plant. It is what’s left of grain crops like wheat, barley, oats, rye and rice once the grain has been harvested.1Wikipedia. Straw The leftovers are bulky, roughly half of a crop’s harvested weight.2Wikipedia. Straw So every field of grain produces a second harvest, one that ends up as bedding, garden mulch, mushroom beds and even house walls.
Which Plants Straw Comes From
Straw is the dry stalk of a cereal plant after both the grain and the chaff, the papery husks around the grain, have been removed.3Wikipedia. Straw Straw names a part and a stage of a plant, not a species. The main straw crops are wheat, barley, oats, rye and rice.4Wikipedia. Straw Farmers grow several kinds of each, such as common and durum wheat, winter and spring barley, and triticale, a wheat–rye cross.5FCA Fertilisants. Straw Cereals: for a Sustainable Cultivation
You can often tell them apart by hand. Wheat straw is golden, fairly stiff and shiny. Oat straw tends to be softer and more pliable, and barley straw is usually softer than wheat with fewer stiff tubes. Rice straw is thinner and leafier, and it is common wherever rice is grown.
Cereal stems make good straw because they are hollow tubes divided by solid joints, which keeps them light yet stiff. Stiffer wheat stems contain more bundles of tough, fibrous tissue that hold the plant upright.6PubMed Central. Effect of stem structural characteristics and cell wall components related to stem lodging resistance in a newly identified mutant of hexaploid wheat (Triticum aestivum L.) That same fibrous wall is what makes dried straw springy and slow to break down.
Even well-cleaned straw is never pure stem. It holds some leaf blades and sheaths wrapped around the stalk, plus the occasional broken grain head. Combines never separate everything perfectly, so a few stray kernels may remain, which is why a straw bale in a garden sometimes sprouts a little green.
Straw from the same crop also varies with the variety grown, the weather that season, and how the crop was harvested, so two wheat straw bales can feel noticeably different. A wet season or late harvest can leave stalks darker and weaker, while a dry ripening season usually gives bright, stiff straw. If you are buying for a specific job such as crafts or thatch-style work, ask the seller which crop and variety it came from.
How Straw Is Made at Harvest
The crop ripens and dries while still standing in the field. Today most grain is then harvested by a combine harvester, a machine named for combining cutting, threshing and cleaning in one pass.7Computers and Electronics in Agriculture. Simulation of grain–straw separation by Discrete Element Modeling with bendable straw particles Threshing, knocking the grain loose from the heads, and sorting grain from straw both happen inside the machine.8Computers and Electronics in Agriculture. Simulation of grain–straw separation by Discrete Element Modeling with bendable straw particles Before combines, crops were cut, tied in sheaves and threshed later, first by hand flails and then by horse-powered threshing machines.
Inside, the cutting header slices the stalks and feeds the whole plant in, where a spinning drum beats the heads against a curved grate so the grain falls through. The remaining straw is carried along and shaken out toward the back, while the grain drops through sieves where moving air blows off the light chaff. Clean grain is lifted into the grain tank. The operator adjusts drum speed and airflow for each crop, because wet or tough crops thresh differently from dry ones. The combine keeps the grain and drops the stalks behind it in a long row, or chops them.
Stalks left in rows on the field are allowed to dry before baling.9TRANSACTIONS of the ASAE. Performance of Large Balers for Collecting Rice Straw For rice, the stalks are often cut close to the ground in a separate pass so more straw can be collected and dried.10TRANSACTIONS of the ASAE. Performance of Large Balers for Collecting Rice Straw After some dry days, a baler pulled by a tractor picks up the rows and presses them into small square, large square or round bales tied with twine. Good straw is baled at around 15 to 20% moisture.11Farm Advisory Service. Alternative Bedding Materials Finished bales are stacked and carted to a barn.
Farmers judge dryness by feel and sound. Dry straw rustles and snaps cleanly when bent, while damp straw bends limply and feels cool. Many also push a handheld moisture meter into a sample bale to check the reading. Morning dew and evening humidity can wet the rows, so baling usually happens in the afternoon after the sun has dried them.
A thick row dries unevenly, with damp stalks underneath, so farmers may rake or turn it to expose the bottom layer to sun and air. Rain on cut straw can darken and weaken it, which is why farmers watch the forecast and try to bale in a dry window.
Not all straw is baled. Many farmers chop it and leave it on the field, which returns material to the soil.
Straw Versus Hay
Hay is grass, clover or alfalfa cut while still green and leafy, then dried for feed. Straw is cut only after the grain has ripened and the plant has died back. Hay therefore keeps most of the plant’s nutrients, while straw’s goodness has gone into the grain. Straw can also be hard for animals to digest: rice straw, with its thick coat of silica on the stems, breaks down more slowly in cattle’s stomachs.12The Journal of Agricultural Science. Effect of silica content on rice straw ruminal degradation
In a bale, hay is greener, leafier and sweet-smelling. Straw is pale gold, hollow-stemmed and nearly scentless. Hay may contain seed heads and flowers, while straw rarely holds grain.
Buy hay to feed rabbits, horses or goats. Buy straw for bedding, mulch or crafts, and note that straw mulch usually carries fewer weed seeds than hay.
Straw works only as a small fibre filler, not a main feed. Cattle and sheep, which ferment fibre in a large stomach, cope with some straw far better than horses or rabbits do. Rabbits and guinea pigs need hay to keep their digestion and ever-growing teeth working properly, so for them straw is only bedding.
Feed stores often sell both in similar-looking bales side by side, and labels like “bedding” or “feed” are the quickest clue. Old, weathered hay can fade to a pale colour and pass for straw, so pull a handful apart and smell it rather than going by colour alone.
What Straw Is Used For
Plowing straw back in each year tends to slowly add carbon and nitrogen to soil, though in most long-term trials the gain was under 10%.13Agronomy Journal. Implications for Soil Properties of Removing Cereal Straw: Results from Long‐Term Studies Straw worked in right before the next planting can even lower that crop’s yield, because soil microbes tie up nitrogen while breaking it down.14Soil Science Society of America Journal. Effects of Residue Decomposition on Productivity and Soil Fertility in Rice–Wheat Rotation Results can swing the other way: in one rice–wheat field, full straw incorporation raised soil carbon by 22% and wheat yield by 58%.15Agronomy. Effects of Full Straw Incorporation on Soil Fertility and Crop Yield in Rice-Wheat Rotation for Silty Clay Loamy Cropland
A plant sown straight into fresh straw can look yellow and stunted. Gardeners can offset this by adding compost or a nitrogen fertiliser when working straw in. Leaving straw on the surface as mulch largely avoids the problem, because the breakdown happens at the contact layer rather than in the root zone. On a farm, chopping straw finely and spreading it evenly helps it break down faster after harvest.
In the garden, spread a few inches of straw as mulch around vegetables. It holds moisture and suppresses weeds.
Whole bales can also become raised beds once conditioned. That means keeping a bale wet and adding nitrogen for about two weeks, so the inside begins to decompose and warms up. When the heat fades, plant seedlings into pockets of compost or potting mix opened in the top. Place the bales cut side up with the strings along the sides, so the strings don’t rot through early. A bale bed lasts roughly one season before it slumps, and then it can be broken up for compost or mulch.
Straw is a classic animal bedding because it soaks up moisture, and oat straw absorbs more than barley or wheat straw.16Farm Advisory Service. Alternative Bedding Materials It gives chickens, horses and pigs a warm, springy nest that traps air in cold weather. The hollow stems keep floors drier, though soiled straw needs regular replacing. Used bedding mixed with manure then becomes a good compost ingredient.
Oyster mushrooms can be grown on plain rice or wheat straw without added nutrients.17PubMed. Oyster mushroom cultivation with rice and wheat straw Growers usually pasteurise the straw by soaking it in hot water to kill competing organisms before adding spawn. The fungus feeds on the straw’s fibres and fruits from it, and the spent straw can go to a compost pile or into garden beds.
Plastered straw bale walls are strong enough to carry the load of one- and two-storey homes.18Construction and Building Materials. Structural Characteristics of Load Bearing Straw Bale Walls They also insulate very well, and properly designed buildings use little energy.19Energy and Buildings. Hygrothermal performance, energy use and embodied emissions in straw bale buildings Plaster finishes without outer cladding, however, showed high mould risk.20Energy and Buildings. Hygrothermal performance, energy use and embodied emissions in straw bale buildings The bales are dense and coated in plaster, so keeping them dry is the key design job, and cladding protects walls from driving rain. Wheat straw can be pressed with glue into particleboard,21Industrial Crops and Products. Physical properties of medium-density wheat straw particleboard using different adhesives or turned into sugars and then ethanol fuel.22PubMed. Production of bioethanol from wheat straw: An overview on pretreatment, hydrolysis and fermentation23Heritage Crafts. Straw hat making – Heritage Crafts24Wikipedia. Drinking straw
Storing Straw Safely
Once moisture climbs above 15%, heat-loving bacteria start to thrive in a bale.25HAYTECH. Hay bales spontaneous combustion Bales packed above 20% moisture can warm to 130–140°F and stay warm for up to 40 days.26Ohio State University Extension. Hay and Straw Barn Fires a Real Danger If heat-loving bacteria take over, temperatures can pass 175°F, risking a barn fire.27Ohio State University Extension. Hay and Straw Barn Fires a Real Danger Bales that feel warm or smell sour should be checked and separated from the rest.
The centre of a large stack holds heat the most, so a stack can feel cool outside while it is warm inside. The first weeks after baling carry the greatest risk, as the straw settles and trapped moisture works its way out.
Start by buying bales that feel dry and light. Stack them off the ground on pallets, or on a layer of gravel, so the bottom bales don’t soak up ground moisture. A roof or tarp with the sides left open keeps rain off while letting air move through, and gaps between bales help airflow. Keep the stack away from buildings and fuel stores so a problem in one bale can’t easily spread, and probe large stacks for heat during the first weeks.
A bad bale shows grey or white dusty mould, a musty smell, or a dark, heavy, damp core. Such straw is poor bedding and can harm breathing.
If you find a warm bale, pull it away from the stack and spread it somewhere open, so the heat can escape and you can see what is happening inside. Don’t keep stacking straw against it, because that traps heat. If a bale smokes or smells burnt, treat it as a possible fire and call the fire service rather than tearing it apart yourself, since fresh air can make a smouldering core flare up.