Almost everyone has started “slips” in a glass of water at one time or another. But there’s a much better way to propagate most houseplants—rooting cuttings in a forsythe pot. Cuttings started in this special pot develop stronger roots that are less likely to rot before reaching transplant size.
Roots that develop this way also make the transition to potting soil more readily than weaker “water” roots, which clump together when removed from their watery environment. Using a forsythe pot is fun, easy, and all but foolproof.
• Clean plastic pot about 8 inches in diameter
• Smaller unglazed terra cotta clay pot, 21/2 to 31/2 inches in diameter
• Paper towels
• Small cork
• Bag of fresh, horticultural-grade vermiculite
• Houseplants such as geranium, peperomia, ivy, heart-leaf philodendron, pothos, African violet, and jade plant.
• This project can be a little messy. Work on a waterproof surface that can be wiped easily.
• You should “top off” the pot with water once every day or two. If the water level goes down more rapidly than that, the small pot is not corked tightly enough.
• You can tell if roots have formed on your cuttings by tugging them gently after a few weeks. If you feel resistance, there are roots. Scoop out the cutting gently, shake off some of the vermiculite, then transfer the cutting to a small container of potting soil.
• You can re-use the container. Just add more vermiculite as you remove cuttings. After several uses, though, it’s best to wash the pots in hot, soapy water, then reassemble with fresh vermiculite.
• For a fun activity for all ages, get together with other houseplant enthusiasts to build forsythe pots. Everyone brings one or two houseplants and shares cuttings. It’s kind of like a cookie exchange, but without the calories!
First, line the bottom of the large plastic pot with a paper towel to cover the drain holes. This prevents vermiculite from sifting through the holes, but allows water to drain freely. Make sure the paper towel doesn’t come close to the top of the pot where it will act like a wick, drying the vermiculite.
Fill the large pot with fresh, dry vermiculite, to about 1 inch below the rim.
Plug the drain hole of the small terra cotta pot tightly with a cork. The forsythe pot’s success depends on a snug fit. If you’re able to find a small clay pot with no drain hole, so much the better. But it must be unglazed terra cotta so water moves freely through its walls.
Screw the corked terra cotta pot into the center of the vermiculite, using a back-and-forth motion. Push it in deeply enough so the top of its rim is nearly level with the top of the vermiculite.
Water the vermiculite slowly. Don’t be too generous at first; excess water will come pouring through the drain holes.
Fill the terra cotta reservoir with water. Because its walls are porous, water will wick through them as moisture evaporates from the vermiculite. All you have to do is keep the reservoir full, and the vermiculite will stay evenly moist.
Stick cuttings into the vermiculite, about 2 to 3 inches apart, in a circle around the reservoir. Take stem cuttings that are no more than 5 inches tall. When taking cuttings, cut them off the main plant about 1/2 inch below a node (photo below), which is the point where a leaf of leaf stem (also called a petiole) is attached to the main stem.
Strip off the lower leaves of the cutting to fully expose the nodes (above). This will also allow you to push the nodes down into the vermiculite. Keep leaves out of the vermiculite to avoid rotting.
Once it's filled with cuttings, place the completed forsythe pot in a bright location. In winter, keep the pot in a sunny window. Move it a little farther from the window in late spring or summer, when sunlight is more intense.
Deborah Brown is professor emeritus, University of Minnesota Department of Horticultural Science, and “Expert Advice” columnist for Gardening How-To.