Wednesday, March 19, 2008

Bracken Ferns

It's spring and I'm pulling out the dry, brown fronds of the bracken fern. 

I love the wide, majestic pattern of the bracken leaves in the spring and summer—like a green, arching umbrellas—which pop up in various areas around my garden. Its delicate and wide pattern is like a fern, but it grows in full sunlight as well as partial shade. I have a difficult time pulling out the few bracken ferns fronds that overgrow my planting of Mexican sage. They can coexist as for as I’m concerned, as long as they don’t snuggle too tightly.

It’s pleasing to know that there is a type of bracken fern on every continent except Antarctica. Having been around for 55 million years means it’s got some pretty hardy genes and few “predators”.

As with all of Nature, there’s a double-edged sword with respect to bracken ferns. The native species of bracken fern is invasive and tends to colonize drier areas of open grasslands, with its dense canopy shading out other plant species. At the same time as it is trying to become the predominate plant in an open meadow, it’s building up a lot of dead fronds which makes fuel for a fire. When a fire races through the grasslands of the meadow competing plants are burned to the ground. The bracken quickly sprouts from its extensive web of rhizomes (horizontal underground stems). This gives it a head start for revegetation over many other plants. And the bracken continues to spread. Such a beautiful foliage and such a persistent plant—maybe why it’s been around for 55 million years. It also walks in the footsteps of mankind, thriving on disturbed soil. 

There’s a reason why brackens tend to huddle together in little herds other than spreading rhizomes. They exude chemicals that suppress the growth of other plants nearby. This is called allelopathy. One plant having a competitive edge over others due to the leaching of unique chemicals into the soil. With bracken ferns, the allelopathic effect may last as long as one year after the plant is gone. An amazing legacy. 

The ash of the bracken is full of potassium (potash). The alkali nature of the ash was a source of potash in the soap industry, glass-making and for making bleach. Then came the cheap alternative sources of alkali in the 1830s. By the 1860 there was no use for bracken ash in commerce.

The use of brackens in a garden is very uncommon. (The young “fiddle heads” are eaten in the spring after being boiled. Yet there is a spooky side, when the foliage is damaged hydrogen cyanide is produced, especially in the younger fronds.I don’t have the nerve to try them given all the toxicity of the young leaves.

But the green, lacy fronds of the spring are good for vegetable gardens. As in Europe, I have gathered the fronds in the spring, when they’re full of vigor and potassium. I dug a wide and deep trench to open the earth. Then I used the gathered fronds to fill the trench nearly half full. Next rich, brown soil is mounded over the freshly-cut foliage. I placed sliced potatoes on top of the warming-spring soil, and a mulch of crisp straw like thin blanket. The searching roots of the potatoes wander through the rich soil and soon find the extra potassium and thrive. These potatoes are more likely to be free of disease. A time-honored style of gardening has slipped “over the pond” from what was the former ruler of our colonies. This easy act of gardening joins two countries by the simple act of gardening. 

Please post a comment - I want to know what you think.

All rights reserved. Copyright 2008

Visit Robert Kourik's web site to learn about his great gardening books.


Bev said...

Hello Robert, just found your blog while Googling for 'bracken nitrogen fixation'.

We are in the Australian bush and have bracken growing as an understorey on our property. I cut the fronds regularly and put them through a small shredder. I use the mulch on my vegetable beds and garden generally. I was aware it is rich in potassium, but just read that it fixes nitrogen like a legume, hence the Googling to confirm, since I wasn't aware of it.

Do you know if it is true?

Anonymous said...

There’s a reason why brackens tend to huddle together in little herds other than spreading rhizomes. They exude chemicals that suppress the growth of other plants nearby. trees for sale