However, until relatively recently, the pressure treating process involved arsenic, a poison that is able to leach out of the wood and into the soil around the wood structure. If you have old pressure-treated structures on your property, or have had them, you'll want to read this article . . .
Poison On Deck!
I've used pressure treated lumber for years, starting with the fence I put up around the yard in the early 1980s and followed by a garden shed and shade house for my plant collection. At the time I wasn't aware of the fact that the chemical used in the pressure treating process included arsenic. Since then, this fact has been brought forward and arsenic is no longer used in treating wood. However, older playgrounds and other structures made of the older wood have been found to have leached arsenic into the soil. This is a bad thing, especially if you have children or pets around your old structures.
So what does arsenic have to do with ferns? Well, for years I've noticed various ferns that would spring up around our place from wayward spores. One of them in particular is quite vigorous and attractive, but not being a fern person, I did not know what kinds were growing. But what I'm going to share here has caused me to look differently at the volunteer ferns and other plants that I see in my garden areas.
Putting the "Brakes" on Arsenic
That particularly vigorous fern is Pteris vittata, also known as the Ladder or Brake Fern. It has a singularly distinguishing feature in that it is able to remove arsenic from the soil. The arsenic is stored in the leaves, which can then be cut off and discarded as they age, taking the arsenic with them. One company, Edenspace, has even taken to marketing these ferns for just this purpose. Edenspace calls their product "Edenfern", but their 'Victory' version is the same Pteris that grows wild in my yard! They also have a variegated type, and one that tolerates cooler temperatures as well.
The use of ferns or other plants to remove toxins from the environment is known as phytoremediation and is an important means of cleaning up these toxins. Other plants also take up arsenic, but the Brake Fern is exceptionally efficient at the job, making it the plant of choice when you have an area you'd like to clean up a bit. Unfortunately, one other plant that accumulates arsenic is rice, which has led to problems in countries such as Bangladesh and India. People who eat large amounts of rice in their diet, and who get their rice from places that have significant arsenic in their soil, are subject to health risks and even cancer because of this. As a result, some researchers are working on the development of rice cultivars that accumulate little or no toxic heavy metals.
Zinc, Cadmium and Uranium, too!
Phytoremediation is a hot area for research, as some plants are able to grow and thrive in places poisoned by excessive levels of zinc, cadmium and other toxic metals. Not only can these plants be used to remove the metals from the soil and thus return it to productive status, they can be harvested to recover the valuable but toxic metals for industrial use. One such plant is Thlaspi caerulescens, commonly known as alpine pennycress. Related to cabbage and broccoli, this little plant can accumulate zinc at levels 300 times that of a typical plant, and cadmium at 1500 times the level of typical plants! At these levels of uptake, normal plants would be killed, but Thlaspi shows no ill effects from such a precocious appetite for these toxic metals. Even such genuinely dangerous substances as uranium and cesium-137 can be taken up by certain plants and removed from contaminated soils.
For more extensive information about this research work, go to Phytoremediation: Using Plants To Clean Up Soils.