A Boston fern that dries out between waterings is not being fussy. NC State Extension says Nephrolepis exaltata needs moist soil that should never be allowed to dry out. Clemson Extension says to keep it barely moist at all times and never let any fern dry out completely.

If your fern keeps drying out faster than you can water it, something about the pot, the mix or the position is working against you. Watering more often treats the symptom. The checks below find the cause.

First, confirm it is drying out

Virginia Cooperative Extension lists these signs of an underwatered houseplant:

  • Wilting, then dry or brittle leaves and brown tips or edges
  • Leaves falling off
  • Dry potting mix that has shrunk away from the pot wall
  • A pot and plant that feel very light

Clemson names too little water as one of the main problems of indoor ferns.

Wilting alone does not settle it. Virginia notes that wilting is the first sign of both underwatering and overwatering. If the mix is wet and the fern still looks limp, read our guide to telling overwatering from underwatering before you add more water.

Cause 1: the pot is full of roots

Boston fern grows fast. NC State rates its growth rate as rapid, and UF/IFAS describes it spreading by thin green runners. Indoors, that growth ends up inside the pot.

Clemson’s houseplant disorders factsheet explains the problem directly. A pot-bound plant has filled its pot with roots. There is not enough soil left to hold water for all those roots, so the plant wilts. The fix Clemson gives is repotting into a larger pot.

How to check: slide the fern out of its pot. A solid mat of roots with little visible mix, or roots circling the wall, means it is pot-bound.

What to do:

  1. Repot in early spring, as Clemson suggests for overcrowded ferns.
  2. Use Clemson’s fern mix: equal parts packaged houseplant potting mix and peat moss or leaf mold.
  3. Loosen circling roots. University of Maryland Extension suggests cutting about 1.3 cm (0.5 in) into the root ball at 5–7.5 cm (2–3 in) intervals and removing dead, brown roots.
  4. Do not jump to a much bigger pot. Virginia warns that an oversized pot leaves roots in a zone that stays too wet.
  5. Consider dividing instead. Clemson says division is the best way to propagate most ferns, and UF/IFAS says Boston fern divides easily.

Cause 2: the mix sheds water

This one fools many growers. You water, water pours out of the drainage holes, and the fern is still dry an hour later.

Virginia Cooperative Extension explains why. Dry potting mixes, especially peat- or bark-based ones, can become hydrophobic, meaning they repel water. Excessive, quick drainage usually means the mix did not take up enough water.

How to check: lift the pot right after watering. If it still feels light, the mix did not wet through. Virginia also suggests sliding the root ball out and looking for dry patches, or pushing a finger into the middle of the pot.

What to do:

  • Give two or three slow applications of water, a few minutes apart.
  • Or bottom water: stand the pot in 5–7.5 cm (2–3 in) of water for 15 to 30 minutes, depending on how dry it is. Hydrophobic mix may take longer, and you may need to refill the tray.
  • Never leave the pot standing in water for more than 60 minutes. Virginia warns that longer soaks risk root rot.

Cause 3: a warm, bright or dry spot

Virginia Cooperative Extension lists the room conditions that speed up drying:

ConditionEffect on the mix
Consistently warm roomMix dries faster, so watering is needed more often
Near a heater or a sunny southwest windowThe container, mix and roots heat up, and the plant uses more water
Bright lightHigher water use and drier mix
Low humidity, especially with the heating onFaster water loss from the leaves, so more frequent watering

NC State recommends 16–21 °C (60–70 °F) and bright, indirect light. Clemson warns never to put ferns directly in a south- or west-facing window. If your fern sits in sun or above a radiator, move it before you change anything else. A cooler, brighter spot out of direct sun slows the drying and suits the plant better.

For dry air, NC State suggests a kitchen or bathroom or a tray of wet pebbles. See Boston ferns in the bathroom for setting one up there.

Cause 4: the pot itself

Pot size and material change how long water lasts:

  • Small pots hold less mix and dry out faster, says Virginia Cooperative Extension.
  • Terracotta loses moisture through its walls. Virginia calls fast drying a disadvantage for moisture-loving plants. Maryland Extension also notes that clay pots dry out rapidly.
  • Glazed and plastic pots do not lose water through their walls, so the mix stays moist longer (Virginia, Maryland).
  • Tall pots drain more, and their upper few inches dry faster (Virginia).

A small terracotta pot combines two of these. Moving the fern into a plastic or glazed pot with drainage holes is a simple first change.

Cause 5: shallow watering

A splash on the surface wets only the top layer. Virginia Cooperative Extension says to water until the mix is wet all the way through, then let it drain until dripping stops. Check for dry spots by pushing a finger 2.5–7.5 cm (1–3 in) into the mix. If you find them, water slowly again.

Virginia also suggests watering in the morning, so the mix drains and the plant takes up water through the day.

Keeping it evenly moist without rotting it

The opposite mistake is just as damaging. Clemson warns that water standing in the pot damages roots. It says root rot usually follows a mix that drains slowly or overly frequent watering.

Ways to hold steady moisture:

  • Check often. Virginia says most houseplants need frequent monitoring rather than a fixed schedule.
  • Double pot. Clemson suggests standing the growing pot inside a second container lined with moist sphagnum moss.
  • Self-watering pots. Virginia says these keep the mix evenly moist over time and suit most houseplants. Check the reservoir regularly and clean it now and then.
  • Ease off in winter. NC State says the plant is dormant in winter and overwatering then can lead to root rot.

After a bad dry-out

  1. Rewet the whole root ball, using bottom watering if the mix sheds water.
  2. Let it drain fully, then empty the saucer.
  3. Prune off fronds that are fully brown. Virginia suggests pruning dead foliage to stimulate new growth.
  4. Judge recovery by new fronds. UF/IFAS notes that severe pruning of a thick clump stimulates new fronds from the roots.

If the fern has shed most of its fronds, cut it back and keep the mix evenly moist. For light, feeding and division, see the Boston fern care guide. For general technique, see how to water houseplants.

References