Do Ferns Need Acidic Soil? A Close Look at Fern pH Preferences

Ferns are a widely varied group of plants. Their native habitats range from the tropics to the Arctic and from deserts to swamps. They can be rough or smooth, juicy or filmy, crown-forming or creeping, lime-loving or lime-intolerant, invasive weeds or almost impossible to grow. Ferns were one of the first plant groups to learn how to live on land. They have since adapted to most conditions and environments, but only a few can handle direct sunlight and low humidity. Most species need moist soil, high humidity and enough shade to maintain these conditions.

Ferns are native to the wild; unlike many flowering plants, like herbaceous perennials, they have not been tamed to grow in gardens. Before you begin your fern garden, observe the ferns growing naturally in your area. Most of these are available commercially. Make sure you put them in your garden in a spot that is similar to the wild places where native ferns grow. Be cautious in your selection. When it grows wild, ferns are likely to grow even more quickly in your garden. If the fern can only grow in a certain place, like wet cracks in rocks, it might be hard to grow in the garden. Grow only those plants for which you have the proper conditions. Never collect ferns from the wild. When you buy ferns, make sure the seller is a reputable one and makes it clear that the plants were grown in a nursery and not in the wild. Selected forms with fancy fronds are always nursery propagated.

In large part, the plants you can grow depend on where in the country you live and garden. Tropical ferns can only be grown in Florida and along the southern coast. The rest of the country has to keep them indoors or under glass. People who live in the southwest can only grow plants that have adapted to lower humidity. People who live in the Midwest, Northeast, Mid-Atlantic, and Upper South can grow most types of woodland plants.

Keep in mind, too, that some ferns have specialized requirements. You can still grow maidenhairs, harts tongues, and other ferns that like alkaline soil even if your soil is more acidic. Adding crushed limestone, oyster shell grit, or cement rubble to the soil will give it a steady supply of lime and make it drain better. It’s not as easy to grow plants that need acidic soil if you live in an area with a lot of limestone. To make the planting bed acidic, work a lot of peat or humus into the soil, use landscape fabric or a two-inch layer of granite grit to separate it from the subsoil, and then add sulfur or ammonium nitrate to the soil. What’s wrong is that the water in these places is probably alkaline, which will change the pH of the soil over time. Under these conditions, its best to grow ferns that prefer limestone, or those tolerant of alkaline conditions. Many types of adiantums, aspleniums, polystichums, dryopteris, and athyriums can grow in a wide pH range. The organic matter in well-prepared soil will help to lessen the impact of too much acidity or alkalinity.

Many ferns have a natural affinity for rocks. Some, like polypodies and the walking fern, can grow right on top of the rock. Others, like cheilanthes and the cliff brakes, need very good drainage and more sun. Most of them like how rocks protect them. The rocks help the soil keep its moisture and create a microclimate that is warmer in the winter and cooler in the summer than the rest of the area. Its important to know which ferns must have limestone and which require acid conditions. Sandstone and granite rocks are often used for foundations that need acid, while limestone or even cement rubble can be used for foundations that need alkalinity. Ferns among rocks should be planted in a well drained but moisture-retentive soil.

For gardeners in most parts of the country, species that have adapted to living in forests are appealing and easy to grow. In most areas, Christmas or sword ferns (Polystichum spp. ), lady ferns (Athyrium spp. ) and shield ferns (Dryopteris spp. ) are commonly found in the wild. These genera contain other non-native species that will grow under similar conditions in the garden. Most prefer a slightly acidic soil with 50 to 75 percent humus, good water retention and excellent drainage. To add humus to your soil, work coarse compost, rotted manure, or fine pine bark into the top 4 to 6 inches. All ferns need a lot of water to grow and a certain amount of humidity to keep their leaves from drying out. Established plants of most woodland species can handle short periods of drought, but that doesn’t mean they will be able to survive conditions that are very dry. Only a very few are adapted to life in bogs or really wet conditions. Swamp, bog and streamside ferns such as the osmundas require more water than most woodland ferns.

Woodland ferns do best in high or dappled shade. The light is almost perfect when it’s cast by large trees, the north side of the house, or a wall that faces the sky. Most woodland ferns will adapt to relatively low light levels, but no ferns thrive in deep shade. Evergreen species are the most tolerant of low light levels. Generally, plants will tolerate more sun and less water in the northern part of their range. When there is more water, they will take in more sun. When there is less water, they will take in less sun.

The nutritional needs of ferns are generally met with compost or the breakdown of leaves. Small size and slow growth are more likely to be caused by limited water than lack of food. In fact, ferns are sensitive to excess fertilizer; quick-release inorganic fertilizers are likely to burn the roots. If supplemental feeding is needed, use well rotted manure, fish emulsion or other slow-release organic food. Wind protection prevents the breakage of brittle fronds and reduces dehydration. Although shelter is helpful, the lowest, most protected area is likely to be a frost pocket, which can delay spring growth and cause early and late frost damage to deciduous ferns as well as the death of species that are only just about hardy enough to survive the winter.

The best time to plant varies according to geographic location. Spring planting is preferable where winters are cold and wet. If you plant ferns in these places too late in the season, the roots might rot before they get established. The rhizomes may be lifted out of the ground by freezing and thawing, which can break young roots and leave them exposed, making them more likely to dry out. If you live in a warmer area, planting in the fall is best because the plant has time to get established before the heat and drought of summer. When you move or plant a fern that is already growing, cut the fronds in half to help it get established and avoid stress from water loss. New fronds usually will be produced as soon as the plant has enough roots to support them.

To move a fern, dig a generous root ball, especially if the plant is in active growth. First, dig a hole that is as deep as the root ball. Then, put the plant in the hole, water it well, and fill in the sides with good soil. Press the soil down around the plant. If the job is well done, the fern may never know it has been moved.

Many ferns available for sale are grown in quart size or larger pots. These are either mature size or will grow to maturity in a year or two. If you want to plant a fern that is in a pot, you need to take it out of the pot and quickly separate the roots. It is important to get rid of extra potting soil, especially if it is very different from the soil in your garden. Potting soils are often light and peaty and will dry out faster than the surrounding soil. This may leave the newly planted fern dry and wilted even though the surrounding soil is moist. To fix it, spread the roots out, mix some potting soil into the root area, give it a lot of water, and then fill the planting hole with good soil. Keep newly planted ferns well watered for the first growing season while they are becoming established.

Plants in pots that are 4 inches or smaller should never dry out until they are fully grown and mature. Plant them in well prepared soil in a protected area. It is often easier to pot them up for special care. Add fine pine bark to any good potting mix to improve drainage. Do not feed until they are growing well. You can add a tablespoon of ground limestone to a gallon of planting mix if the fern needs acidic soil.

Ferns that are sent to you may have been taken out of their pots and put in plastic bags, or they may have almost no roots at all. When you unpack the plants make sure that the growing tip has not been damaged during shipping. If the fern is broken or rotting, it probably won’t grow back, and the shipper should be told right away. Depending on its size, either plant the fern in a protected area or pot it up and make sure it gets plenty of water until it can stand on its own. If the roots look dry, put the plant in water for an hour or two while you get the planting area ready.

You can buy some ferns as small plants with no roots that come in a plastic bag filled with dry peat moss. In theory, the bag has enough moisture to keep the plant from drying out. In practice, though, ferns don’t like being bare-rooted, and while they will rot if they are surrounded by wet peat, they are usually dry enough that they need time to recover. If you can’t see real signs of growth, like a crozier starting to uncurl, you should stay away from plants that don’t have roots. Often the growing tip has been damaged by handling, or the peat has become completely dry. If you do decide to buy these ferns, give them a couple of hours to soak in water and then plant them in potting mix that drains well. Be careful to keep the growing tips at or above soil level. Keep well watered and transplant to the garden after they have become established. Another disadvantage of ferns sold bare root is that they are frequently dug up from the wild.

How far apart should you plant your ferns? Spacing depends on form, size and type of growth. These crown-forming plants have upright rhizomes and a vase-shaped shape. They spread slowly and look best as a single crown. Goldies fern and some polystichums and osmundas that grow taller may need at least three feet of space between plants. Oak and beech ferns spread quickly and can be planted fairly far apart. The hay-scented New York and Virginia chain ferns spread even more quickly. The ostrich fern, on the other hand, has runners that spread far and should only be planted in areas where it can be controlled.

Both fern fronds and roots grow directly from the stem, which is also known as the rhizome. The stem tip is where all new growth starts, so if it gets hurt, the whole plant could die. The roots grow at the base of the fronds, or on the lower side of creeping rhizomes. In all ferns they are close to the surface and easily disturbed.

Rhizomes that grow straight up make a clear crown with tightly wound croziers at the soil’s surface. These croziers grow into a whorl of fronds that spread out like a vase from the center in the spring. These may grow out of the ground to form small trunks. Then, the roots that grow at the base of the fronds are open to the air and can get dry. Crowns that lift off the ground need to be replanted to get them back to the same level as the soil. Adding one to two inches of mulch each year may make replanting unnecessary.

Rakes, hoes and feet do not belong in the fern garden. Surface roots, tightly coiled croziers and developing fiddleheads are too easily damaged. Make a path for people to walk on, and remove evergreen fronds that have been burned by winter and any other garden waste by hand before the fiddleheads start to grow in the spring.

If you pick plants that do well in your area and clean up after yourself in the garden by getting rid of any trash that pests could hide in, you may not have to deal with diseases or pests very often. Usually, slugs and snails are the ones that cause trouble. They eat a lot and do well in places where ferns do. Slug baits containing metaldehyde are effective, but they are toxic and especially hazardous to children and pets. Various nontoxic baits and traps are safer: Dishes of beer sunk to soil level are effective. When grapefruit shells are turned over, slugs will gather under them. For the final blow, they can be dropped into denatured alcohol. Ferns are quite sensitive to insecticides. If you must use a chemical poison, test it on a few plants. Avoid the liquid emulsion sprays, as they contain oils that damage ferns. Use dusts or sprays made from wettable powders, reducing the recommended dosage by one half.

To prevent disease, start with healthy plants. Keep the crown of the plant above the soil, and dont cover it with mulch. Avoid overwatering and space the plants far enough apart for adequate air circulation. Adding fine pine bark, pine needles, or a fairly coarse compost as mulch will help keep the soil moist, stop weeds from growing or at least make them easier to pull, and give your ferns almost all the nutrients they need. Every year, add more mulch to make up for the fact that some athyriums and dryopteris plants like to grow their crowns above ground level.

Which Ferns Are for You?

Ferns for Beginners

• Adiantum pedatum
• Athyrium filix-femina
• Blechnum spicant
• Cyrtomium species
• Cystopteris species
• Deparia acrostichoides
• Dryopteris dilatata
• Dryopteris erythrosora
• Dryopteris expansa
• Dryopteris filix-mas
• Dryopteris marginalis
• Matteuccia struthiopteris
• Polystichum acrostichoides
• Polystichum munitum
• Polystichum setiferum
• Thelypteris noveboracensis

Ferns for Sun

• Athyrium filix-femina
• Dennstaedtia punctilobula
• Dryopteris filix-mas
• Dryopteris ludoviciana
• Matteuccia struthiopteris
• Onoclea sensibilis
• Osmunda cinnamomea
• Osmunda regalis
• Polystichum setiferum
• Sphaeropteris cooperi
• Thelypteris kunthii
• Woodwardia virginica

Ferns for Deep Shade

• Asplenium rhizophyllum
• Blechnum spicant
• Cyrtomium falcatum
• Dryopteris (evergreen species)
• Gymnocarpium species
• Osmunda cinnamomea
• Polystichum species
• Phegopteris species
• Woodwardia areolata

Ferns for Wet Soils

• Athyrium filix-femina
• Blechnum serrulatum
• Dryopteris celsa
• Dryopteris ludoviciana
• Macrothelypteris torresiana
• Onoclea sensibilis
• Osmunda cinnamomea
• Osmunda regalis
• Thelypteris kunthii
• Thelypteris palustris
• Woodwardia species

Ferns for Dry Soil

• Asplenium platyneuron
• Blechnum penna-marina
• Cystopteris bulbifera
• Dennstaedtia punctilobula
• Dryopteris filix-mas
• Dryopteris intermedia
• Dryopteris marginalis
• Osmunda claytoniana
• Pentagramma triangularis
• Polypodium species
• Polystichum species
• Phegopteris hexagonoptera
• Woodsia obtusa

Ferns for Alkaline Soils

• Adiantum species
• Asplenium (most species)
• Cystopteris bulbifera
• Diplazium pycnocarpon
• Dryopteris carthusiana
• Dryopteris dilatata
• Dryopteris expansa
• Gymnocarpium robertianum
• Matteuccia struthiopteris
• Osmunda claytoniana
• Polystichum aculeatum
• Thelypteris palustris

Ferns for Strongly Acidic Soils

• Asplenium platyneuron
• Blechnum species
• Cyrtomium species
• Dennstaedtia punctilobula
• Dryopteris campyloptera
• Dryopteris cycadina
• Dryopteris ludoviciana
• Gymnocarpium dryopteris
• Osmunda cinnamomea
• Osmunda regalis
• Polypodium species
• Polystichum species
• Phegopteris connectilis
• Thelypteris species
• Woodsia obtusa
• Woodwardia species

Nancy Swell grows and propagates a wide variety of hardy ferns in her garden in Richmond, Virginia. She is a passionate fern lover who is a member of The American Fern Society, The British Pteridological Society, and The Hardy Fern Foundation.

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Acidic Soil Plants List

Do ferns like acidic soil?

Most of the ferns like acidic soil. Ferns exhibit the best growth in the acidic to neutral soil. pH from 4.0 to 7.0 is suitable for the fern to grow. Though ferns like acidic soil, some ferns such as maidenhair ferns prefer alkaline soil in order to grow. Most of the ferns like acidic soil. Soil pH ranges from 2 to 6 is termed acidic soil.

Do ferns need fertilizer?

Soil: Ferns sink their thirsty roots into deep, friable soil rich in organic matter. Heavy clay soils are not hospitable unless amended with compost. A neutral or slightly acidic soil is preferable for most ferns; aim for a pH between 6.0 and 7.0. Fertilizer: Beyond compost added to the soil, ferns do not need fertilizer.

Do Boston Ferns prefer acid or alkaline soil?

Boston fern prefers acidic soil. Boston fern grows best in the low pH condition ranges from 5 to 5.5. Boston fern is also named the royal fern as they grow in lower pH conditions. Do ferns prefer acid or alkaline soil? Do ferns tolerate acidic soil? Most of the ferns prefer slightly acidic to neutral soil.

Can ferns grow if soil pH drops?

Though ferns prefer slightly acidic soil, ferns can’t grow if the soil pH drops drastically. Coffee grounds make the soil drastically acidic. Ferns can’t tolerate such acidic soil conditions and the growth of the ferns drastically decreases.