All plants require 16 distinct nutrients to survive. Boston fern (Nephrolepis exaltata “Bostoniensis”) is no exception, but it needs them in much smaller quantities than most plants. This tropical fern grows year outdoors in U.S. Department of Agriculture plant hardiness zones 10 through 12, but can be grown indoors in pots, or in hanging baskets to dress up porches in the summer. Whether you develop the fern outside or indoors, its nutrient demands would be the same; how many times you feed it though, depends on the time of year.
Fern Signals
Both overfertilizing and underfertilizing that a Boston ferns impact the foliage. Too much fertilizer turns fronds brown, beginning at the tips; not sufficient fertilizer causes fronds to lose their colour and become a pale green. Boston fern requires supplements containing sulfur, phosphorous and potassium on a regular basis to keep it healthy and lush. Supply these through a water-soluble fertilizer when fronds begin to lose their colour or at fixed intervals, depending on the season.
How Much to Fertilize
Whether you develop Boston fern outside or indoors, fertilize it with a balanced, overall purpose fertilizer, such as 20-20-20, combined at half the strength recommended on the label. Bear in mind that the tag will recommend a greater quantity of fertilizer for plants grown indoors than for plants grown in pots outside or in beds. For instance, the tag for 20-20-20 fertilizer recommends mixing 2 tablespoons fertilizer to 1 gallon of water to get houseplants and 2 teaspoons each 1 gallon of water to get outside plants. To mix 20-20-20 at half strength, combine 1 tablespoon fertilizer using 1 gallon of water to get houseplants, and one teaspoon fertilizer with 1 gallon of water for outdoor plants.
When to Fertilize
When ferns are actively growing, they require more nutrients than when growth slows down during cooler weather. Fertilize ferns once per month from around April through September. During cooler autumn and winter months, fertilize every two to three months, or any time you see the frond colour fading. For plants in pots, drench the soil with the fertilizer solution until water starts to run from the drainage hole.
Fish Emulsion
If you want an organic fertilizer, Boston fern reacts well to fish emulsion. For outdoor potted plants, blend 1 tablespoon fertilizer in 1 gallon of water to treat 1 cubic foot of soil. Don’t dilute the amount recommended on the label. Feed outdoor ferns once per month year-round. For indoors plants, mix 2 teaspoons fish emulsion in 1 quart of water. Pour the solution on the soil until it runs out the drainage hole of the pot. Feed indoor ferns once per month throughout summer and spring, but withhold fish emulsion in autumn and winter unless frond color turns pale green. Fish emulsion does not store well when combined with water, so mix only what you plan to use instantly.