Blackberry bushes (Rubus allegheniensis) and bracken ferns (Pteridium aquilinum) propagate in very different ways. Blackberry spreads mainly through its roots and canes, and bracken multiplies through spores scattered by the wind. These two plants do have several things in common, however. Both provide food and shelter for birds, animals and insects. Both are considered invasive in some regions because they crowd out other plants. Bracken and blackberry are difficult to eradicate once they are established in the home landscape.
Put on canvas gloves and protective clothing to prevent injury from thorns. Wear safety glasses to protect your eyes if the bushes are higher than your waist.
Cut down blackberry bushes at their trunks with long-handled pruning shears. Do this in the autumn, after harvest, when leaves are gone and you can see better what you are doing.
Chop the bushes into manageable size, place in garden waste bags and discard.
Till the area with a tilling machine to a depth of 45 cm (18 inches), immediately after cutting the blackberry bushes. Rake out roots and rhizome fragments with a garden rake. Bag and discard them.
Till the area again in spring and again the following autumn. Tilling just once will cause the blackberry rhizome and root fragments to spread and regrow. Repeat tilling will eventually kill them.
Cut down the bracken ferns in the autumn, before the foliage dies back, using a grass whip on large areas or grass clippers for smaller groupings of fern.
Rake up, bag and discard the foliage in garden waste bags to prevent spores from dispersing and spreading the fern the following year.
Cultivate the area with a pitchfork to a depth of 30 to 37.5 cm (12 to 15 inches). The tines of the pitchfork will pull rhizomes to the surface where you can see and collect them without breaking them up. Bag and discard the rhizomes.
Plant a cool-season grass like fescue or Kentucky bluegrass, or a ground cover like myrtle or English ivy in the area, to help crowd out any rhizomes that may be left in the soil.
Dig out any rhizomes that you missed that sprouted in spring. Cut them back before the fronds unfurl. Repeat cutting back whenever you see one. Eventually (after two to three years), the remaining rhizomes will starve and die from lack of nutrients.
Clean your cutting equipment after attacking bracken ferns. Cleaning will remove spores from the blades and prevent dispersal to other areas of the landscape.
Don't try to control blackberry bushes with mowing. You will only stimulate more growth and disperse seeds over a wider area.