Sowing Proso Millet: Warm Soil, Shallow Seed and a Stand That Comes Up Level

Sow into warm soil, and sow late rather than early

Proso millet is one of the few grains you can afford to sow late. From sowing to a cuttable seed head is roughly 60 to 75 days in warm weather, which is short enough that a sowing made well after everything else in the garden still finishes comfortably. That short season is the whole reason to grow it, and it means you should never be tempted to gamble on cold ground the way you might with a long-season crop that needs every week it can get.

The number that matters is soil temperature at one inch (2.5 cm), taken mid-morning on three days running. Below 60F (16C) the seed simply sits; germination is slow, uneven and heavily raided by ants and ground beetles. At 65F (18C) you get emergence in five to seven days. At 70F (21C) and above the seedlings are through in three to five days and, more importantly, they are all through within about a day of each other. Even emergence is worth far more in this crop than in most, because the seed head ripens unevenly enough on its own without you adding a two-week spread at the start.

In practice this places proso millet two to three weeks after your last frost, later than sweet corn in the same bed. It is also a genuine second crop: after early peas, after garlic, after an overwintered green, there is almost always enough season left. Count backwards from your first expected frost, allow 75 days plus two weeks of margin for curing weather, and if the arithmetic closes, sow.

Depth: half an inch, and not a fraction more

Sow half an inch (1 cm) deep, three quarters of an inch (2 cm) at the very most in light sandy ground. Proso seed is small and round with a limited food reserve, and a seed buried an inch and a half (4 cm) down exhausts itself before the shoot reaches light. This is the single most common reason a sowing fails outright, and it usually happens because someone applied corn depths to a seed a tenth of the size.

The trade-off is that shallow seed depends entirely on the top inch (2.5 cm) staying moist for the four or five days it takes to germinate. Water the bed thoroughly the day before you sow so the moisture is settled and even, sow into it, and then keep the surface just damp with a light sprinkle each morning until you see green. Once the seedlings are up you can stop babying it; from that point on this is a crop that asks for less water than any other common cereal.

Firm the soil over the seed. A loose, fluffy seedbed leaves small round seed suspended in air pockets where it never makes contact and never germinates. Press the row down with the flat of a rake until the surface is visibly compressed.

1. Water the ground a day ahead Soak the bed 24 hours before sowing so the top four inches (10 cm) are evenly moist. Sowing into pre-moistened ground and covering gives far better emergence than sowing dry and watering afterwards, which caps the surface with a crust that shallow-sown millet cannot push through.
2. Scratch a shallow furrow, not a trench Draw a furrow half an inch (1 cm) deep with the corner of a hoe or the edge of a board. If you can see your furrow clearly from standing height it is too deep. Rows twelve inches (30 cm) apart are ample; proso is a small, fine-stemmed plant and does not need corn spacing.
3. Sow thickly and thin later Drop seed roughly every half inch (1 cm) along the row. Home-saved or packet proso rarely germinates above 80 percent, and a thick sowing thinned back beats a thin sowing you try to patch. Thin to two inches (5 cm) between plants once the seedlings are three inches (8 cm) tall.
4. Cover, firm, and keep the surface damp Rake soil back over, press it down along the row, and mist or sprinkle each morning until emergence. Stop the daily watering the moment the row is green; after that the crop wants deep, infrequent water instead.

Broadcasting is an option and it is how proso is grown at field scale, but in a garden bed it makes the volunteer problem worse and makes hoeing impossible. Sow in rows you can walk between.

How much to sow, and where to put it

A bed of about forty square feet (4 square meters) sown in rows twelve inches (30 cm) apart is enough to give a household a real quantity of grain and to be worth the threshing effort. Below about twenty square feet (2 square meters) the harvest is more of a curiosity than a crop, though it is still a perfectly good way to learn the plant before committing a larger bed.

Choose the driest, sunniest bed you have, and choose one you are willing to see millet in again. Proso wants full sun and free-draining soil. It does not want the rich, damp corner where you grow squash; heavy nitrogen and abundant water push it into soft growth that flops in the first storm. A bed that was manured last season rather than this one is close to perfect.

The siting decision also has a long tail. Spilled grain at harvest germinates the following spring and for several springs after, so put proso where a few years of volunteer seedlings will be easy to hoe out, not in a permanent bed or among perennials where you cannot get a blade in.

Write the sowing down before you forget it

Record the date you sowed, the soil temperature you measured, and the date the row turned green. Three seasons of those three numbers will tell you more about the right sowing window in your own garden than any general guidance can, because emergence speed in proso is almost entirely a function of your soil warming curve.

Note the bed as well, by name or by a sketch of the plot. You will want that record next spring when unexplained grassy seedlings appear, so you can tell volunteer millet from a weed and decide whether to hoe or to let a few run. Add the row spacing you used and whether the stand was too thick or too thin at heading; that is the note that actually changes what you do next year.