How to Fertilize Boston Fern
Nephrolepis exaltata
Reviewed by Kiersten Rankel M.S.
Quick Answer
Feed your Boston Fern with a balanced liquid fertilizer (20-20-20 or 20-10-20) diluted to half strength every 4-6 weeks during spring and summer. Ferns are salt-sensitive, so less is more. Stop feeding entirely in winter when growth slows.
When Should I Start Feeding My Boston Fern?
Boston Ferns are tropical perennials (zones 9a-12b) grown as houseplants in most of the U.S., so feeding timing follows seasonal light levels rather than outdoor frost dates.
Pacific
Mar–Oct
Mountain
Apr–Sep
Midwest
Apr–Sep
Northeast
Apr–Sep
Southeast
Mar–Oct
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How Often Should I Fertilize My Boston Fern?
Feed every 4-6 weeks from spring through early fall. Boston Ferns grow at a moderate pace and do not need frequent feeding. If you notice browning leaf tips, you may be feeding too often or at too high a concentration.
In winter, stop fertilizing entirely. Growth slows significantly with shorter days, and unused salts will accumulate in the soil. If your fern is under grow lights year-round, you can give one quarter-strength feeding per month through winter.
Feeding Calendar
Spring & Summer
Half-strength liquid every 4-6 weeks
Early Fall
One final quarter-strength feeding, then stop
Late Fall & Winter
No feeding
What Is the Best Fertilizer for Boston Fern?
Boston Ferns do well with a balanced liquid fertilizer like 20-20-20 or 20-10-20. They are not heavy feeders and their roots are sensitive to salt buildup, so always dilute to half the label rate. A quarter-strength dose is even safer if you tend to fertilize frequently.
Avoid granular or slow-release fertilizers in hanging baskets. The salts concentrate in the small soil volume and can burn the fine root system. Liquid feeding gives you better control over how much your fern actually receives.
Synthetic
Water-soluble balanced formula that dissolves cleanly. Use 1/2 teaspoon per gallon for ferns.
Affordable liquid concentrate. Use 3-4 drops per quart of water for a gentle half-strength dose.
Organic
Gentle organic liquid perfect for salt-sensitive ferns. Apply at full label strength since the NPK is already very low.
Top-dress the soil with a thin layer every 2-3 months. Releases nutrients slowly and won't burn sensitive fern roots.
How Do I Fertilize My Boston Fern?
1
Water your fern first
Always water thoroughly before fertilizing. Boston Fern roots are fine and salt-sensitive, and dry roots absorb fertilizer too quickly, leading to burn.
2
Dilute to half strength
Mix your liquid fertilizer at half the label rate. For a 20-20-20 concentrate, that typically means half a teaspoon per gallon instead of a full teaspoon.
3
Pour evenly over the soil
Apply the diluted solution directly to the soil, not onto the fronds. Work your way around the pot so all roots get an even share. Let excess drain from the bottom.
4
Flush the soil every few months
Run plain water through the pot until it flows freely from the drainage holes. This washes out salt buildup that can damage the fine root system over time.
5
Watch the fronds for feedback
Healthy feeding shows as bright green new growth from the center. Brown leaf tips or yellowing lower fronds can signal too much fertilizer. Scale back if you see these signs.
Got More Questions?
Why are my Boston Fern's leaf tips turning brown?
Brown tips are the most common sign of salt buildup from fertilizer. Flush the soil with plain water and reduce your feeding frequency or concentration. Low humidity can also contribute, so check both.
Can I use coffee grounds on my Boston Fern?
Coffee grounds are mildly acidic, which ferns do appreciate. However, they compact easily and can attract fungus gnats in indoor pots. A better option is to water occasionally with diluted cold coffee (1 part coffee to 4 parts water).
What happens if I over-fertilize my Boston Fern?
Ferns are more sensitive to over-fertilizing than most houseplants. You will see brown or crispy leaf tips, yellowing fronds, and possibly white salt crust on the soil surface. Flush the pot with plain water several times to wash out the excess.
Should I fertilize a newly repotted Boston Fern?
Wait 4-6 weeks after repotting before fertilizing. Fresh potting mix has enough nutrients to get your fern started, and the roots need time to recover from the transplant.
Can I use slow-release granules for my Boston Fern?
It is better to avoid them, especially in hanging baskets. The small soil volume makes it hard to control concentration, and the salts can build up and burn the fine root system. Liquid fertilizer gives you much more control.
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About This Article
Kiersten Rankel M.S.
Botanical Data Lead at Greg · Plant Scientist
Editorial Process
Fertilizer recommendations verified against Nephrolepis exaltata growth data from Greg's botanical database, cross-referenced with USDA hardiness zone data and published horticultural research.
20,860+ Greg users growing this plant
USDA hardiness zones 9a–12b
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