How often to water Boston fern

The interval

A Boston fern is watered about every 4 days in the growing season and about every 7 days in winter. 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. The Royal Horticultural Society says to water moderately with soft water while it grows and sparingly in winter.

The margin is narrower than for most houseplants. NC State Extension says the fern needs moist soil that should never be allowed to dry out, and the pot should never stand in water. Push a finger 1 to 2 cm into the compost and water when it feels just dry at that depth, not before. Lift the pot too. A fern in a snug pot of moist compost is noticeably heavier than the same pot on the day it needs water.

Water from the top with soft water, such as rainwater, at room temperature, until water runs from the drainage holes, then empty the saucer after ten minutes. The RHS warns that fronds can rot if they become too wet, so pour at the base and not over the fronds. Humidity is high for this plant. Mist lightly about every 2 days, in the morning so the fronds dry, or set the pot on a tray of wet pebbles, in a kitchen or bathroom, as NC State Extension advises.

Too much water gives root rot, which NC State Extension warns of in winter. Too little, or dry air, gives brown, crisp fronds, and NC State Extension notes that scale and spider mites become a problem if the air is too dry. A fern that has dried out badly can be cut back to a few centimetres above the compost, kept humid and just moist, and it pushes out a full head of new fronds.

What is particular to this plant is how narrow the margin is. It dislikes both a dry pot and a wet one more than most houseplants do, and a slightly snug pot is easier to keep evenly moist than a large one, so repot only when the roots fill the pot, and go up one size at a time.

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