Home Gardening Keep the fern in the same pots they come in, every other day submerge them in a 5 gallon bucket filled with 1/2 cup of epson salts 3 gallons of regular water until the soil stops bubbling, then hang up to drip dry… ferns will be dark green, glossy, and 3×3 by September from ferns that start out with 7 fronds in May.