S → P → S′

How to play

• Sow. Seed does not keep: most of it dies within a year. Sow it into free land, or spend it on expansion, before it is gone.
• Wait. A rosette flowers after three or four years, sheds its seed, and dies. That is the only way the stand grows: S → P → S′, where S′ is always far larger than S.
• Expand. Land, not seed, is always short. New land opens as history allows: the wind first, then rivers, gardens, railways and farms.
• Hold on. When the stand is full and nothing can be bought, years pass quickly. The drill ends by itself.

Field notes

• The figures are those of the literature where possible: about 20,000 seeds per plant, four or five plants per square metre, 8.8 per cent of buried seed alive after a year (see Umbel and Seed bank).
• The dates are those of the plant’s history: Kew in 1817, Shelford in 1828, the silage programme in 1947 (see Lag phase and Sosnowsky’s hogweed).
• Stands invaded for about thirty years decline, as their soil turns against them (see Enemy release hypothesis).