Insights
Caring for Ferns: Keeping Pongas and Ground Ferns Happy
Ferns carry a reputation for being fussy that they do not deserve. In the bush they grow in the leanest soil on the shadiest banks, and they will do the same in a garden. Nearly every fern failure comes back to one of two things: they dried out, or they were planted in the wrong light.
Start with position. Most ferns want dappled or full shade with shelter from drying wind. The south side of the house, under established trees, or the shaded strip along a fence line are all prime fern territory. Morning sun is fine for the tougher species; hot afternoon sun scorches fronds on almost all of them.
Soil matters less than moisture. Ferns like ground rich in organic matter that stays damp without sitting in water. Dig plenty of compost or leaf litter through the planting area, and mulch generously every year. Fallen leaves left where they land are exactly what ferns evolved with, so a fern corner is one part of the garden where tidiness works against you.
Tree ferns need one extra piece of understanding: the trunk is part of the root system. Water a ponga at the top of the trunk as well as the base, especially in its first couple of summers, and never let the crown dry out. When planting a tree fern, keep the trunk vertical and firm it in well, but do not bury it deeper than it stood before. A daily hose over the trunk through the first dry season is the single best thing you can do for a new ponga.
Feeding is simple: ferns are light feeders, and a spring dressing of compost or a half strength general fertiliser is plenty. Strong fertiliser burns the fine roots and browns the fronds, so if in doubt, feed less.
Maintenance is mostly restraint. Trim off fully brown fronds at the base in late winter, but leave anything with green in it, because the plant is still drawing on it. Watch for scale insects on the underside of fronds, which wipe off or respond to a light oil spray.
Given shade, moisture and mulch, a fern planting gets better every year with almost no input, and few plantings feel more like New Zealand than a bank of healthy ferns under a ponga canopy.