Uneven Growth in a Boston Fern

Potting Medium

• Boston ferns need a potting medium that retains enough water so they won’t dry out too quickly, but it should also drain well and be well aerated. A good mixture is 50 percent coarse peat with 50 percent perlite or vermiculate added to help it drain. A soil pH between 5 to 5.5 pH is ideal. Soil below 7 is acidic or “sour”; soil above 7 is alkaline or “sweet.” To increase pH, add dolomitic lime or wood ash; to decrease it, add aluminum sulfate or sulfur. You can buy kits to measure soil pH at most garden supply centers.

Best Temperatures

• Boston ferns grow best at a night temperature of roughly 65 degrees Fahrenheit and daytime temperatures that do not exceed 95 F. Nighttime temperatures of 68 F will speed the development of young plants while mature plants thrive on 62 F nighttime temperatures. Boston fern fronds will unfold best and grow to the maximum length at average daily temperature of 77 F.

Water and Fertilizer

• Keep the soil consistently moist, reducing watering from fall through late February. If the soil dries, a Boston fern may shed some fronds. If this happens, prune the fronds to about 2 inches long so they can regenerate. They like high humidity; one way to give them that is to set the pot on a tray of wet pebbles. Growing them near a kitchen or bathroom will help give them humidity. Growers typically recommend a "weak" liquid solution of 20-20-20 houseplant fertilizer once a month from spring to early autumn. The definition of a weak solution is slippery and depends on the specific fertilizer, but it generally means about 1 heaping teaspoon of granular fertilizer dissolved in 2 1/2 gallons of water. Do not fertilize when the potting soil is dry or apply too much fertilizer. Too much fertilizer can cause salts to build up in the potting soil, drying out the tips of the fern's roots and stunting its growth. If you see a white film on the top of the potting soil or a white crust in the drainage hole, it is a sign that you are watering the fern too much or applying too much fertilizer. (See Reference 5)

Light

• Boston ferns growing under artificial lights like between 2,500 and 3,500 foot-candles of light. Full daylight is 1,000 to 10,000 foot-candles. Direct sunlight is 10,000 to 100,000 foot-candles. If you’re not technically inclined and armed with light meters and artificial lights, put your Boston fern close to a south-facing window or in an enclosed sun porch.