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Sorghum runs a single, uninterrupted arc: it goes in when the soil is properly warm, it grows fast through the hottest part of summer, it heads in late summer, and it ripens into autumn. There is no second sowing and no succession planting worth doing, because the crop needs the whole warm season to finish. That makes the calendar simple to hold in your head and the individual decision points correspondingly important.
The arc is described in growth stages rather than dates, because sorghum is grown from the tropics to short-summer temperate gardens and the same crop can be sown across a range of several months depending on where you are. What is constant is the sequence and the intervals between stages. Anchor your own calendar on the date the heads emerge from the boot and everything downstream follows from it.
| Stage | Timing | What you do |
|---|---|---|
| Bed preparation | Two to three weeks before sowing | Work in a moderate balanced feed, level and firm |
| Sowing | Soil at 2 in (5 cm) holds 65-70F (18-21C) | Sow 1 in (2.5 cm) deep, thicker than final spacing |
| Emergence | 4-8 days after sowing | Note the date the stand is complete, not the first seedling |
| Thinning | Seedlings 4-6 in (10-15 cm) | Cut extras at ground level to the spacing for your type |
| Knee high | 3-5 weeks after emergence | Side-dress nitrogen, hill soil against the stems |
| Rapid growth | Through the hottest weeks | Dawn leaf check only. Water when rolled at dawn |
| Boot stage | Head enclosed in the top leaf sheath | Water regardless of leaf signs. Stop feeding |
| Head emergence | Head clears the boot | Record the date. Everything downstream counts from here |
| Flowering | 3-7 days after emergence, top of head down | Do not let the crop dry out |
| Soft dough | About 20-25 days after heading | Net or bag heads against birds |
| Hard dough to black layer | About 35-45 days after heading | Grain can be cut. Syrup cane is at peak sugar |
| Dry | 1-3 weeks after black layer | Thresh and store, or cut earlier and finish under cover |
The decisions that actually matter
Most of the season needs nothing from you. Sorghum grown in warm ground with restrained feeding is close to self-managing through midsummer, and the temptation to intervene during a drought pause is the main way people make it worse. What the calendar really consists of is five decision points, each of which closes and cannot be revisited.
Miss the soil temperature and you get a gappy stand you will live with all season. Miss the thinning window and roots have knit and you cannot fix the spacing. Miss the knee-high side-dress and hilling and you get a lightly-fed crop on a narrow base. Miss the netting at soft dough and the birds take it. Miss the harvest window and you either lose grain to shattering or, for syrup, you lose the sugar to starch conversion. Everything else is watching.
- Decision one: is the soil warm enough yet Measure at two inches (5 cm) mid-morning on three consecutive days. Below 60F (16C) do not sow at all. This decision is made once and governs the evenness of the entire crop.
- Decision two: what spacing does this type want Made at four to six inches (10-15 cm) of seedling height. Grain goes to four to six inches (10-15 cm) apart, syrup and broom to six to eight inches (15-20 cm). Once the seedlings are a foot (30 cm) tall the roots have knitted and thinning damages what stays.
- Decision three: feed and hill at knee height One side-dress of nitrogen and one ridge of soil drawn against the stems, both at eighteen to twenty-four inches (45-60 cm) of height. This single visit determines both head fill and whether the stand survives a storm.
- Decision four: protect the heads at soft dough Net the block or bag individual heads the moment the seed squashes into a paste rather than squirting. Waiting until you see bird damage is waiting too long, since a flock can strip a small block in three days.
- Decision five: cut, or leave it standing Once the black layer has formed, nothing more enters the grain. Cut and dry under cover if birds are active or rain is forecast, or leave it standing to dry if the weather is settled. For syrup cane, cut and press the same day, and cut the whole block ahead of any forecast frost.
If you are growing more than one type, run a separate calendar for each. Grain, syrup and broom sorghum diverge completely from the boot stage onward, and a single set of dates covering a mixed planting will have you cutting one block three weeks late.
The end of the season and what follows
Frost ends sorghum. It is not frost-hardy at any stage, and a crop caught green by a hard freeze does not recover. That gives the calendar a hard back edge, and the whole plan should be laid out so that the black layer arrives at least two weeks before your usual first frost date. If it does not, you were either too late sowing or you are growing a type that needs a longer season than you have.
After harvest, the stalks are substantial and slow to break down. Chop or shred them before composting or turning them in, or they will still be recognizable next spring. There is a nitrogen cost to incorporating that much dry carbon, so if you are following sorghum with a hungry crop, either compost the residue elsewhere or add nitrogen when you turn it in. Sorghum roots also leave the soil in good structural condition, having gone deep in search of water, which is a genuine benefit to whatever follows.
Do not leave shattered grain lying on the bed if you can avoid it. Rake up what you can. The volunteers that come up next season are young green growth of the kind that carries the highest prussic acid levels, which is a hazard worth eliminating rather than tolerating in a garden where animals or poultry range.
Building a calendar you can reuse
Convert everything to intervals rather than dates, and anchor on two observations: the date the soil hit 65F (18C) and the date the heads cleared the boot. Written down for two or three seasons, those two dates plus the intervals between the stages that followed give you a calendar that fits your garden rather than a general region, and one that adjusts itself automatically to a cold spring or an early summer.
Keep a note of which type went where, along with its final spacing and its height at maturity. Sorghum types are indistinguishable early and unmistakable late, and a season-old record of block positions saves a surprising amount of confusion when you are deciding what to sow where next year. Record the frost date against the crop stage too, since the margin you actually had is the number that tells you whether to sow a week earlier next season.