How Cold Is Too Cold For Ferns?

They are beautiful.

That’s why you grow ferns in your garden. But how much cold can they tolerate?

A temperature below 30° Fahrenheit (-1° Celsius) is too cold for most ferns, and they won’t survive. Some species of ferns can survive up to -50° Fahrenheit (-45° Celsius), but those are rare ones growing in climates of the Arctic or Antarctic.

In this post, I’ll let you know about some ferns and how much cold they can survive. I’ll also let you know when you should bring your ferns indoors and where to place them.

So let’s take a look.

How cold is too cold for ferns?

The gorgeous feathery fronds of ferns bring to mind the peaceful atmosphere of humid forests in tropical regions.

Although most ferns thrive in warm, damp climates, the fern is a remarkably diverse plant species. With over 10 000 subspecies, a few fern species have adapted to colder climates like the Arctic and Antarctic and can survive at -50° Fahrenheit (-45° Celsius) temperatures.

Despite a few notable exceptions, most ferns will need help surviving temperatures below 30°Fahrenheit (-1° Celsius).

This common fern thrives in USDA zones 3 through 8 and requires almost no maintenance, according to “Fine Gardening.” (gardenguides.com)

Kimberly Queen Fern temperature tolerance

The Kimberly Queen Fern (Nephrolepis obliterate), native to Australia, can be tricky to keep in cold environments. This stunning evergreen fern prefers to grow in shade or partial shade and thrives in temperatures between 60° to 70° Fahrenheit (15° to 21° Celsius).

Unlike some of its more robust relatives, the Kimberly Queen Fern does not do well in cold climates and is best suited to USA Zones 9 and 10. USA Zone 9 experiences low temperatures of 20° to 30° Fahrenheit (-7° to -1° Celsius), with most Zone 9 and 10 states being located along the Southern coastlines and Deep South.

Based on the Kimberly Queen Fern’s hardiness rating (Zone 9 and 10), we know that the Kimberly Queen Fern will die in temperatures below 20° Fahrenheit.

Boston Fern temperature tolerance

Listed as being hardy in Zone 10 – 12, the Boston Fern (Nephrolepis exaltata) prefers to grow in temperatures between 65° to 75° Fahrenheit (18° to 24° Celsius). Daytime temperatures of 75° Fahrenheit that gradually drop to 65° Fahrenheit during the night are ideal for the Boston Fern.

The roots of potted Boston Ferns have less soil insulation and protection than Boston Ferns planted in the ground and thus are more vulnerable to cold damage. Potted Boston Ferns need to be moved indoors at temperatures at or below 45° Fahrenheit, while planted Boston Ferns only need protection at temperatures below 30° Fahrenheit (-1° Celsius).

In addition to their poor cold tolerance, Boston Ferns are heat-intolerant; they will need to be moved to cooler areas when temperatures exceed 95° Fahrenheit (35° Celsius).

Boston Ferns do not thrive in areas known for dramatic temperature fluctuations, even if the temperature fluctuations occur within the acceptable range for Boston Ferns, i.e., 30° to 95° Fahrenheit (-1° to 35° Celsius).

Macho Fern temperature tolerance

The Macho Fern (Nephrolepis biserrata)is significantly taller and broader than the Kimberly Queen Fern and Boston Fern, but like the Kimberly Queen Fern prefers the USA Zones 9 and 10.

Native to Louisiana, Florida, and Hawaii, Macho Ferns do well in any location with a similar environment to these states, with winter temperatures no lower than 20° to 30° Fahrenheit (-7° to -1° Celsius).

While the Macho Fern is an excellent outdoor plant for Zone 9 and 10 states, gardeners can successfully grow these plants in colder conditions if cared for properly.

Macho Ferns grown in Zones 8 and 7 will need to be pruned and brought in during the cold winter months as they rarely survive with prolonged exposure to below-freezing conditions.

What temperature should you bring ferns inside?

You should bring ferns inside when the temperatures drop below 25° to 30° Fahrenheit (-3° to -1° Celsius). The USA hardiness rating for ferns specifies this. However, experienced gardeners recommend transferring your fern indoors at slightly warmer temperatures.

It can be challenging deciding on when to bring your ferns indoors, especially as there are so many different types of ferns with their individual preferences for growing conditions and temperature tolerance.

The golden rule to keep your fern alive in cold weather is, know your fern! This may seem like a ridiculously simple statement, but if you know where your fern species grows naturally, you will have the key to keeping your fern alive.

Ferns growing in warm tropical climates typically need temperatures between 60° to 75° Fahrenheit (15° to 24° Celsius) to thrive but can tolerate gradual temperature changes between 20° to 95° Fahrenheit (-7° to 35° Celsius). Few ferns fair well when forced to undergo rapid temperature changes.

Potted ferns are more vulnerable to cold damage than planted ferns and thus need to be moved indoors at warmer temperatures. Potted plants are typically 10° to 15° Fahrenheit less cold-tolerant than planted ferns, i.e., most tropical potted ferns need to be moved indoors when temperatures fall below 45° Fahrenheit (7° Celsius).

Can a fern survive frost?

A fern can survive frost if it’s native to the cold region and it’s a light frost that goes away. Ferns categorized as cold-resistant Zone 3 to 8 are better at surviving occasional frost. Ferns classified as Zone 9 to 12 plants are rarely frost-resistant and develop severe frost damage if left unprotected.

Your ferns’ natural water content will form ice crystals during freezing conditions, damaging the delicate plant cells.

Damage to the plant cells manifests as yellow, wilting leaves, which eventually turn black or brown as they become crispy desiccated remnants of their lush, summer bloom.

However, not all ferns are cold-averse. Ferns native to the area will typically survive a light frost. The frost may cause the above-ground foliage to die and fall off, but the healthy root system should see the summer resurrection of your fern.

Examples of cold-hardy ferns:

1. Lady Fern (Athyrium filix-femina)
2. Japanese Painted Fern (Athyrium niponicum f. pictum)
3. Male Fern (Dryopteris filix-mas)
4. Ostrich Fern (Matteucia struthiopteris)
5. Sensitive Fern (Onoclea sensibilis)
6. Cinnamon Fern (Osmunda cinnamomea)
7. Royal Fern (Osmunda regalis)
8. Christmas Fern (Polystichum acrostichoides)

Where should ferns be placed indoors?

Ferns should be placed indoors in shaded rooms away from direct sunlight. These ferns prefer shaded or semi-shaded areas and can be damaged by direct sun exposure.

Most ferns make good household companions as the temperature range for tropical ferns is similar to the temperatures humans enjoy. You won’t need to turn your house into a sauna or exotic hothouse for your fern to survive!

How do you take care of indoor ferns in the winter?

Before moving your fern indoors, make sure it is clear of pests, is not root bound, and is small enough to be easily managed indoors.

It would be best if you placed your fern in a room with moderate ambient light and away from cold drafts and breezes.

It’s essential that the room’s humidity is kept between 45% to 60% and that the temperature remains a cool 65° to 72° Fahrenheit (18° to 22° Celsius), although the ideal temperature will differ between fern species.

Ferns spending the winter months indoors should not be fertilized and need minimal watering; watering them once a month is usually sufficient.

Do ferns come back every year?

Ferns will come back every year as most are perennial. They will die back every winter and regrow next summer as long as the winter temperatures don’t drop below the fern’s temperature tolerance levels.

Prolonged periods of cold and severe frost will be fatal for tropical ferns preferring warm climates.

Rugged ferns like the Ostrich Fern may surprise gardeners with a last jubilant regrowth in autumn after their initial loss of foliage.