Rooting Media

Wednesday, January 25, 2012
Just as some plants root best from snipped tips while others resist all but a root cutting, some plants are faster to root in one medium than another. In addition, the kinds of roots that emerge from different media can vary and ultimately affect plant growth. Each medium has its advantages and I’ve used them all with decent success. Here’s my experience with some of them, and I’ll blog about more options next week. Perlite is dusty stuff, but quite efficient for rooting plants that are sensitive to rot such as poinsettia. It is fractured volcanic glass that has fractures that create a very particular shape that resembles lots of tiny spheres fused together in circular patterns. It is porous and dries out well, which allows good air circulation in the root zone and forms thick, white roots. To avoid inhaling perlite dust, wear a mask when you scoop or pour it out, and then water perlite lightly as soon as you get it out of the bag. Use it in small, new plastic pots or cells or wash previously used containers, rinse well and rinse again with a 1:10 solution of bleach and water. Stick the cuttings and water in with a liquid Hormex solution. Keep the pots damp but not wet while using perlite to root cuttings. Sand, but not just any sand, works well for rooting lots of plants. However, much like water, sand produces mostly adventitious roots that may be thin and rather fragile. The best sand for rooting plants, and for general use in the garden, is known as sharp sand. It is contrasted from round river sand by its irregular shape. Round particles clump together and stay very wet while sharp sand’s pointy edges separate so water and roots can get through. Sometimes sharp sand is labeled as such, but more often you’ll find it in masonry sand or play sand made for children’s sandboxes. I use sand for rooting canes of dieffenbachia and ti plant, along with green plants like the indestructible coleus that primarily form adventitious roots, anyway. Ground, aged bark can be used as a rooting medium alone or in combination with with perlite and/or sand. When roots form in pure bark, they can be thick and stubby which is sometimes desirable but not always. Bark is porous and allows faster drying out of the root zone, helpful for rooting many woody plants. If cuttings fall over because bark is too porous, mix it half and half with sand or perlite, or use all three in equal portions. Water pots or flats of bark and bark mixes before sticking cuttings and keep them moist. If drying out seems to occur too often, use a plastic cloche to increase humidity around the containers. Sphagnum moss is long-fibered and not solid at all. It is the go-to medium for creating air layers. Too often overlooked, air layering can rescue a corn plant that has leaves only at the top of a tall caned stem. I like to use air layering on woody plants and fruit trees that have stems between ¼ and 2/3 inch in diameter. I did not know that sphagnum moss is a wise choice for rooting terrestrial orchids until I attended an Orchid Society meeting years ago. Since then I’ve adapted the member’s method to start many new orchids from stems and broken joints. It could not be simpler: wet the moss and squeeze it out so it is damp but not dripping and fill a plastic pot with it without tamping it down. Make a fresh cut on the orchid stem, dip it into fresh Hormex, and slip it into the sphagnum. Water lightly and consistently and look for new roots in a month.
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