How to overwinter a Boston fern – 5 easy steps to keeping your fern happy through the coldest season

Ferns are one of my favorite plants to grow, both indoors and outdoors. The texture and shape their foliage brings to a space is truly mesmerizing and elegant. Boston ferns are a top choice, with their sword-shaped fronds that can be grown and displayed in an endless number of ways.

Boston ferns can be grown as houseplants or you can grow Boston ferns outdoors in containers, hanging baskets or even borders. They're hardy to US zone 9 to zone 11 and are one of the best ferns for shade, tolerating darker spots in the yard. However, these ferns aren't tolerant to frost and will need to be overwintered if grown outdoors.

Luckily, it's incredibly easy to overwinter a Boston fern to make sure it gets through the harshest season unharmed. Simply follow the key steps below.

5 steps to overwinter a Boston fern

Overwintering a garden involves preparing any tender plants for the frosty weather they can't cope with.

'The Boston fern can tolerate cold weather but can't withstand frost. It may get damaged after prolonged exposure to temperatures below 41–45°F,' notes Nastya Vasylchyshyna, botany expert at Plantum.

Overwintering Boston ferns involves a bit of tidying up and relocation. Here's what you need to do:

1. Bring your Boston fern indoors

The first thing to do when overwintering a Boston fern is think about giving it a new location for the coldest season. Luckily, because these plants are among the best ferns to grow indoors, transitioning your Boston fern inside is straightforward.

'If your fern is growing in a container garden, the easiest way to protect it from frost is to bring it inside,' says Nastya. You should aim to do this in fall before early frosts.

You can then care for your Boston fern as you would when growing it as an indoor plant: 'Place it in a bright, cool or moderately warm room that has a temperature of around 63–72°F,' says Nastya. 'Don’t expose the plant to drafts or place it near heating appliances, as it will cause the fern to dry out,' she adds.

If you aren't growing your outdoor Boston fern in a pot, it's advisable to lift it, pot it up and bring it indoors. Take care not to damage any roots when doing this.

Another key step here is to check for any pests hitching a ride on your Boston fern. There are plenty of methods to prevent pests when bringing houseplants back indoors that can be applied here. This will ensure your fern doesn't pass on any problems to other overwintering plants or houseplants.

Nastya Vasylchyshyna

Nastya Vasylchyshyna is a professional botany expert for the Plantum app that helps identify plants and plant diseases and provides care recommendations. For 4 years she has consulted on botany-related topics for Plantum. Her specialization is plant morphology, phytopathology, and plant physiology.

2. Prune away dead and damaged foliage

When overwintering plants indoors, it can be easy to think you don't need to do much to keep them happy. However, Boston ferns should still receive optimal care during the overwintering period. This includes making sure it's in the best possible shape.

'Boston ferns should be pruned before it gets cold, especially if you plan to keep the plant indoors in a cool room during winter dormancy,' says Nastya. She advises trimming off dry and browning fronts at the top of the plant, as well as any large older fronds at the bottom of the plant to a length of three-five inches. 'Don’t prune young fronds that are just starting to unfurl,' Nastya warns. You likewise shouldn't remove more than a third of the plant at a time, as this can stress it out.

Cutting back your Boston fern before winter will remove any damaged foliage that energy is being wasted on and encourage bushier growth when the temperatures start to rise again.

You should always use essential gardening tools to make clean cuts and avoid making pruning mistakes. These bypass pruning shears from Amazon can help you get the job done.

3. Reduce watering

As with other plants that aren't actively growing through winter, it's imperative to reduce the amount of water you give your Boston fern. This fern grows during the warmer months and doesn't require as much moisture when outside temperatures are lower.

'Avoid overwatering during winter, as this can lead to root rot and kill the plant,' warns Nastya.

These ferns don't enjoy drying out or being overly wet - incorrect watering could cause your Boston fern to turn brown. I always use a soil moisture meter (available at Amazon) to identify when to water my indoor plants.

'Let the top soil dry slightly, but don’t let the entire soil ball dry out, just keep the substrate constantly moderately moist,' says Nastya. 'If your Boston fern is in a cool place like a garage or if it’s outdoors in a mild winter climate, you only need to water your plant once every three to five weeks,' she adds.

4. Insulate your Boston fern's container

This step is important for those keeping a Boston fern somewhere sheltered but chilly - like a garage or conservatory.

As Boston ferns aren't among cold-tolerant houseplants, even placing them in a colder spot indoors can have an impact on their health. Using burlap wrap, like this from Amazon, or something similar, wrap your fern's container to keep the roots sufficiently warm through winter.

This is a simple way to provide extra insulation for plants that don't cope well with lower temperatures.

'You can also insulate with straw or frost-protection fleece,' suggests Tammy Sons, horticulturist and CEO of TN Nurseries.

Tammy Sons

Tammy Sons is a horticulture plant expert, garden writer, and educator. Tammy is the CEO and founder of TN Nursery, a thriving online plant nursery based in Altamont, Tennessee. She is also a prolific writer, sharing her knowledge through articles on various gardening topics, including plant care, sustainable landscaping, and the latest trends in horticulture.

5. Move your Boston fern back outdoors in spring

Having successfully cared for your Boston fern during the overwintering period, you can plan to move it back outdoors. It isn't necessarily as easy as putting it back in its original spot, however.

You'll need to keep an eye on your local weather forecast to see when late frosts in spring have passed. The ideal night temperature for Boston ferns is around 65°F. Any cooler can risk damage to its health. Moving your Boston fern outdoors too early could risk it being caught in the last of the freezing temperatures.

You may also need to reacclimatize your Boston fern to an outdoor setting, just as you would when moving houseplants outdoors. Try placing it in a warmer spot out of direct sunlight to protect it from leaf scorch.

FAQs

Should I fertilize my Boston fern during winter?

You shouldn't fertilize your Boston fern during winter. These ferns don't actively grow during the colder seasons, so fertilizing them during this time risks oversaturated soil and root burn. It's best to only fertilize your Boston fern in spring and summer. Always follow manufacturer instructions when doing so.

Does my Boston fern need high humidity during winter?

Boston ferns thrive in humidity, thanks to their native forest habitat. Keeping humidity levels up during winter is a good idea if you want to keep your Boston fern happy. This is most easily done by overwintering a Boston fern indoors and treating it as a houseplant. You can increase humidity for houseplants in a number of ways, including placing them close to other plants, misting them or using a humidifier (like this one from Amazon).

Once spring has come around and you're preparing to move your overwintered plant back outdoors, try propagating your Boston fern through division. It's simple enough to divide plants to multiply them, just take care not to cause any damage to roots.