How to care for outdoor ferns in pots

Growing ferns outdoors in pots or containers allows you to choose the perfect conditions for any fern variety. That flexibility is a great advantage to planting in pots, but there are also some complications to bear in mind, compared to planting ferns directly into the ground.

Growing ferns outdoors in pots or containers will succeed best when you take care to choose the best size and material of pot, the ideal potting mix for the fern species, and water on a regular schedule. Other key aspects of outdoor fern care in pots are to protect against temperature stresses, feed the fern when the soil becomes exhausted, and divide and repot once the plant is root-bound. With these few steps, outdoor potted ferns can thrive, and add a stylish accent to a porch, deck or courtyard.

A great advantage of growing ferns in pots is that you can tailor the growth conditions to perfectly suit the variety you are growing. You can also position the ferns in the ideal spot for sun and wind protection, and you can use the pot itself to add an artistic touch to your garden design. However, there are some common issues that need to be considered to ensure that your potted ferns grow bushy and reach their full potential.

What type of pot is best?

The first consideration is the size and material of the pot needed. In general, ferns have shallow root systems and so do best in smaller pots, or shallow planters or container gardens. For most fern varieties, the rhizomes and roots will penetrate less than a foot into the soil under normal conditions, so deep pots will not offer any advantage, but might make it difficult to keep the hydration of the soil correct. 

Another factor is the pot material. Plastic pots will be good for retaining moisture, and are inexpensive, but not noted for their beauty. Plastic pots also provide little insulation in hot or cold temperatures, meaning that the roots can become stressed in hot weather (unless regularly watered) or freeze in hard winters. Alternative materials like terracota, clay or ceramic are much more attractive choices, and provide better insulation. However, terracota and clay pots can “breathe” and so allow for evaporation of water in dry weather or become discolored if overwatered. Glazed ceramic pots can be a good all round choice – with aesthetic appeal and protection against water loss or absorption.

Finally, good drainage from the pot is essential, as otherwise there is a risk of overwatering, leading to root rot if the soil becomes waterlogged.

What potting mix is best for outdoor ferns?

The best potting mix will depend somewhat on the specific fern variety that is chosen, but a good general rule of thumb is to use a standard all-purpose compost mix supplemented with a physical conditioner such as grit or perlite to improve drainage.

For varieties such as Japanese painted ferns, Lady ferns, or the various types of Boston fern, a specialist mix for acid-loving plants can improve growth, or a 50:50 mix of acid-loving and all-purpose formulations.

Japanese painted fern

  • Athyrium niponicum
  • Deciduous
  • Prefers partial shade
  • Height: up to 0.5 m
  • Soil: acid, neutral or alkaline. Moist, well-drained.

Lady fern

  • Athyrium filix-femina
  • Deciduous
  • Prefers partial or full shade
  • Height: up to 1 m
  • Soil: acid or neutral. Moist, poor drainage tolerated.

Boston fern

  • Nephrolepis exaltata
  • Evergreen
  • Partial shade
  • Height: up to 1 m
  • Soil: acid or neutral. Moist, well-drained.

How often should you water ferns in outdoor pots?

The watering needs of pots will be greater than ferns grown direct in the ground. However, the frequency of watering will of course depend on how often it rains, assuming that the pot is placed in the open air, rather than under a porch or veranda.

As ferns generally prefer smaller or shallower pots, a downside is that the soil can dry out more quickly. Regular watering is needed through dry spells, typically at least two or three times a week. If the temperature gets very high, daily watering may be required. Fortunately, there are simple ways to tell if your fern is getting the right amount of water.

Finally, potted ferns will need less water during the fall and winter months when the plant will be dormant. At these times a greater risk is for freezing of the crown of the fern – or even the whole soil mix itself.

Another strategy for helping maintain the right level of humidity and temperature for ferns is to cluster lots of posts close together. This creates a sort of microclimate, where moisture is pooled after watering, and any evaporation can be captured by the overhanging foliage. If the pots are also collected near the wall of a house, then warmth can also be trapped near to the plants, protecting against the worst of the cold weather.

Do you need to fertilize potted ferns?

In general, ferns need minimal fertilizing. For very bushy and lustily growing specimens it can be worth supplementing with a diluted, balanced fertilizer through the growing season (50% dilution in water of a standard 10:10:10 formulation is fine). This should only be added monthly, and should not be necessary until the fern has grown mature in the pot for at least a couple of years, at which point the soil can become depleted.

When should you repot outdoor ferns?

Many growers believe that ferns actually like being pot-bound, or at least that they can thrive even when their roots are densely packed. This reflects the tendency of ferns to adapt to poor soil conditions that resemble their natural habitat of rocky ground and shallow soil.

Ferns are tough

There will come a point, however, where a fern can grow so fulsome that its growth becomes arrested, even if it does not start to die. At that stage, it is time to either repot into a larger container, or to divide the root-ball and repot the divisions into several new pots.

A sign that it is time to repot a fern is a decrease in the number and length of new fronds growing in spring compared to previous years. This suggests that the plant’s reserves of nutrients or energy are exhausted. Other indicators are roots poking out of the drainage hole at the base of the pot, and a ring of brown and withered fronds around the base of the plant, suggesting that the foliage is getting too dense and crowded. 

Should you bring pots in over winter?

There are two main reasons to bring potted ferns into cover in the winter. First is that the fern is not hardy down to the temperatures seen in your area. Boston ferns, for example, make for excellent summer decoration in most of the US, but can only survive the winters outside in the milder southern and coastal states.

The second main reason to move pots indoors is if the pot itself is fragile. Terracotta, clay, or ceramic pots can become brittle at low temperatures, and once a crack or flaw sets in, repeated freezing and thawing during hard frosts can cause the pot to break.

If either of these risks are an issue, then moving the pot into a garage, porch or utility room will allow the fern to survive the winter. Low light conditions, and moderate temperatures are ideal, because ferns will typically remain dormant through the winter, so need little watering and no fertilizer. If conditions are too warm and dry the fern may suffer from the lack of humidity, and will need more regular watering.

Outdoor pots offer a range of possibilities to use ferns cleverly and stylishly in the garden. With attention to a few key details of soil, water and climate, they can thrive throughout the year.

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