How often to water rosemary

The interval

Rosemary has two regimes. A new plant, and any plant in a pot, is watered about every 12 days in the growing season. An established plant in the ground is not watered at all outside a severe drought. In winter a pot wants water about every 30 days, and often less. Growing season means the warm, bright months from spring to early autumn, roughly March to September in the northern hemisphere and September to March in the southern. Winter is the cold, short-day part of your own year, when the danger is wet roots.

The Royal Horticultural Society says new plants should be watered during dry spells in their first year and that, once established, rosemary shouldn't need additional watering in the ground. Pots dry faster in hot weather and need more water, but the compost must never be waterlogged. Check by pushing a finger 5 cm into the compost and lifting the pot. A pot that is dry that deep and light in the hand is ready.

Soak and dry means watering slowly until water runs from the drainage hole, then leaving the pot alone until the compost has dried right out again. The RHS advises a soil-based compost with up to a quarter horticultural grit, a pot with drainage holes and no standing saucer. Humidity is low for this plant, and it grows best where the air moves.

Wet roots are what kill rosemary. NC State Extension says overwatering is the common cause of plant decline or death, and that rosemary has a low tolerance for wet, humid environments. The RHS says cold, wet compost can cause roots to rot and die, and that rosemary hates wet roots, especially in winter. A rosemary that has gone dry in a pot is a smaller problem than one in damp compost, because a soak puts it right.

What is particular to this plant is where it comes from. NC State Extension says it is found in dry, rocky areas around the Mediterranean, and tolerates drought, salt and heavy pruning. A dry week is no hardship, and a wet fortnight in winter is. Shelter the pot from rain rather than from a mild frost, and group potted plants against a wall.

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