Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
Once in a while I come across a new to me flower that is so spectacular it literally stops me in my tracks. That’s what happened the first time that I saw Bear’s Breeches. The leaves were incredible. The flowers were spectacular. I had to have it for my own garden.
What is Bear's Breeches?
Bear’s breeches (Acanthus mollis) is a herbaceous perennial that is native to the Mediterranean. It is often referred to simply as “acanthus”. The plants are pictured in both the Greek and Roman art and sculpture. In fact, I unknowingly became familiar with acanthus leaves in college when I learned the different architectural styles of classical pillars. Depictions of acanthus leaves are found on the capitals of Corinthian columns.
Bear’s breeches have been gracing our gardens since ancient times. The first written mention of them growing in Italian gardens was in 1548. William Robinson, a British garden writer, mentions the plants in his famous book, The Wild Garden, in 1870. Peter Henderson, who owned a nursery in New Jersey, mentions them in his book, Handbook of Plants in 1890.
Acanthus are hardy in zones 7 – 10, but they grow very well in my New Jersey zone 6 garden. The secret to getting them through the colder winters of zones 5 and 6, is to cover the crowns with a thick layer of mulch in the fall. Be sure to remove the mulch in the spring when the plants start growing again.
The plants are large, up to 3 feet tall and 3 feet wide. The leaves grow in a clump, up to 2 feet long. They are evergreen in warmer climates. In colder climates, it’s best to not clear away the dead foliage in the fall. Leave it to protect the crown over the winter.
The flowers grow on a spiny stalk and look a lot like snapdragons. There can be up to 120 flowers on each flower stalk. The flowers appear to be purple and white, but the purple is actually a bract that covers the white flowers. The flowers are exclusively pollinated by bumble bees and large bees that are strong enough to force their way inside the flower to the nectar. Bloomtime is late spring to early summer for approximately 3 to 4 weeks.
The flowers are followed by a pod that contains 2 – 4 seeds. Acanthus depends on the wind to disperse its seeds.
How to Grow Bear's Breeches
Bear’s breeches grow in either full sun or partial shade. They need a minimum of 4 hours of sunlight each day. If your plants aren’t blooming, they are probably not getting enough sun.
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Plant them in rich, well-drained soil. Once established, they are drought tolerant. They grow best, though, with 1 inch of water every week. The plants don’t need to be fertilized. A side dressing of compost in the spring is sufficient.
Space your plants 3 – 4 feet apart. Acanthus unfortunately is invasive. It spreads by both seed and underground runners. A good way to keep them under control is to plant them in a pot and sink the pot into the ground. You can also surround your plants with a barrier sunk into the soil around them. Deadhead the flowers to prevent them from producing seed.
How to Divide Bear's Breeches
Bear’s breeches have long taproots so it is difficult to dig them up and divide them. A better way to propagate them is to stimulate the plants to grow plantlets that can be transplanted elsewhere. In the fall, take a shovel and thrust it into the base of the plants. Leave the plants alone all winter. In the spring, you will see little plants sprouting from the wounds you made with your shovel the previous fall. Use a sharp knife to cut the plantlets with roots from the parent and replant them where you would like new plants to grow.
Be aware that it will be a few years for these small plants to get big enough to bloom.
How to Grow Bear's Breeches From Root Cuttings
Acanthus is usually propagated by root cuttings. You can take your cuttings either in the fall or the early spring. Carefully dig up your plants and using pruners or a sharp knife, cut no more then 1/3 of the roots that are the width of a pencil. Replant your plants.
Clean the roots, cutting off any lateral roots and the thin tip. Then cut the roots into 2 -4 inch lengths. Make a horizontal cut through the top and an angled cut at the bottom.
Plant the root pieces, flat end up and 1/8 inch deep in containers. Keep the soil moist. You can carefully transplant your cuttings into your garden when they are 2 inches tall, after the last frost when the soil has warmed.
These new plants will not bloom immediately. They need a few years to grow large enough to support flowers.
How to Grow Bear's Breeches From Seed
Bear’s breeches have long taproots so they do not transplant well. It is best to start your seeds outdoors in your garden rather than indoors.
You can sow your seeds directly into your garden in the spring, after your last frost and when the soil has warmed to 45⁰F. To hasten germination, soak your seeds overnight to soften the hard outer seed coat. The following day, plant your seeds in your garden ½ inches deep and 6 inches apart. Keep the soil moist. Germination should begin in 3 weeks and last about a month. Thin the seedlings to 3 feet apart. Mulch your seedlings to keep the soil moist and prevent weeds from growing and competing with your seedlings for water and nutrients.
It will be several years before the plants are large enough to start blooming, so be patient.
© 2020 Caren White