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Spring oats go in as early as the ground can be worked to a crumb without smearing. Earlier is better with oats in a way that is not true of most garden crops, because the grain fills best in cool weather and every week of delay pushes flowering closer to summer heat. Oats germinate down to about 40F (4C) and will sit quite happily in cold wet soil that would rot a bean, so the risk of sowing too early is small and the cost of sowing too late is a thin, pinched harvest.
Autumn oats sown as a winter killed cover need six to eight weeks of growing weather before hard frost, which usually means going in around the time you are pulling the last of the summer crops. Sown that early they build a knee high mass of leaf and a dense root plate before the cold shuts them down. Sown late, they make a thin fuzz that frost flattens into nothing and gives you no weed suppression at all through winter.
In a mild winter region an oat sown in autumn behaves like a winter grain: it stays green, tillers through the cold months and heads the following early summer. This gives a longer season and usually a heavier crop than spring sowing, but only if your winter minima stay above roughly 15F (-9C). Below that, plan on losing the stand.
| Sowing | Timing | What it is for | Sowing to harvest |
|---|---|---|---|
| Spring grain | As soon as soil is workable, soil above 40F (4C) | Grain to eat or store | Four to five months |
| Autumn cover | Six to eight weeks before first hard frost | Winter killed weed mat and soil cover | No harvest, turn in at spring planting |
| Autumn grain, mild winter only | Six to eight weeks before first frost | Overwintered grain crop | Eight to nine months |
| Late summer forage | Eight weeks before frost | Green cut for fodder or compost | Cut at eight to ten weeks |
Depth, spacing and rate
Oat seed is sown about one inch (2.5 cm) deep, a little shallower than wheat and a good deal deeper than most vegetable seed. In a light sandy bed or in a dry spring go to an inch and a half (4 cm) so the seed sits in moisture; in a heavy wet soil stay at three quarters of an inch (2 cm) so it can push through. What you are aiming at is the crown, the point just below the surface where the tillers and the crown roots come from, and burying that too deep costs the plant a week of energy it spends pushing the shoot up rather than making leaf.
Rate is where garden growers get it wrong, and they always get it wrong in the same direction. Oats are grown as a stand, not as individuals. Each plant makes only two to four productive panicles, so the yield comes from having a great many plants standing shoulder to shoulder, and a thin stand yields poorly and fills with weeds. Sow about one and a half ounces of seed per square yard (45 g per square meter) for grain, and heavier, up to two and a half ounces per square yard (75 g per square meter), for a cover crop where you want a smothering mat rather than plump grain.
Rows six to eight inches (15 to 20 cm) apart are worth the small yield penalty in a garden. They let you hoe between the rows in the first month while the stand is still open, they let you see where germination has failed, and they give you somewhere to put your feet when you come to net the crop against birds. Broadcasting is faster and slightly more productive per square foot but leaves you locked out of your own bed.
- Rake the bed to a fine tilth Oats germinate from close contact with moist soil, so break down the clods to something roughly pea sized. Do not add manure or a nitrogen rich feed at sowing. Oats on rich ground grow tall, soft and top heavy and go flat in the first summer storm, which is the single most common way a garden oat crop is lost.
- Draw shallow drills an inch deep Run the corner of a hoe or the edge of a board down the bed at six to eight inch (15 to 20 cm) spacing. A consistent depth matters more than a precise one, because a drill that wanders between half an inch and two inches gives you a stand that emerges over ten days instead of four and ripens just as unevenly.
- Scatter the seed along the drill, not spaced out Aim for grains falling roughly half to one inch (1 to 2.5 cm) apart along the row. Do not try to place them individually; take a pinch and trickle it. If you can count the grains as they land you are sowing far too thinly.
- Cover and firm Draw the soil back over the drills and press it down with the flat of a rake or by walking the bed on a board. Firming is what pulls moisture up to the seed and it is the step most often skipped. Loose soil over oat seed gives patchy emergence even in a wet spring.
- Water once, then leave it Give the bed a thorough soak if the soil is not already damp, then do not water again until the seedlings are up unless the surface dries hard. Emergence takes five to ten days in cool soil, longer at the cold end. Watering a bare bed daily crusts the surface and holds the shoots back.
- Net or cover if birds are a problem Pigeons and finches will strip a freshly sown oat bed, and they will come back for the seedlings. A single layer of row cover or fine netting held clear of the soil for the first two weeks solves it. Remove it once the plants are three inches (8 cm) tall and no longer worth the birds' effort.
Thinning, gaps and what to expect early
You do not thin oats. The stand is meant to be crowded, and the plants sort themselves out by tillering less where they are tight and more where they are loose. Resist the instinct that a vegetable garden has trained into you. The only intervention worth making in the first month is pulling out broadleaf weeds by hand from between the rows before the canopy closes, after which the oats shade out almost everything themselves.
Gaps are worth patching in the first fortnight. A bare patch a foot square will fill with weeds and stay a weed patch all season, because the surrounding oats cannot spread sideways into it. Sow the gap with fresh seed as soon as you see it and it will catch up close enough to be harvested with the rest.
Emergence looks like grass, because it is. The first leaf is narrow and rolled, unfurling into a smooth blue green blade with no hair on it and a distinctly anticlockwise twist, which is one of the small ways you can distinguish an oat seedling from a wheat or a stray weed grass. Within four to six weeks the plant starts tillering, throwing new shoots from the crown, and the bed stops looking like a lawn and starts looking like a crop.
Write down the sowing date, the seeding rate you used and where you got the seed, and next season compare that against how the stand looked at four weeks. Two years of those notes will tell you more about the right rate for your soil than any general figure, because rate depends heavily on how good your seedbed is.