Calluses Are A Good Thing When Rooting Houseplants

african violet plant

Any leaf with a bit of stalk (petiole) attached will form a new plant, after callusing.

I think it’s always worth it try to root a house plant cutting. Even though winter isn’t the ideal time, it can still be done. As Helen Lewis, of Mastering Horticulture says: “Plants are super-organisms.  Given the right environment most plant tissues can regenerate into new plants.” When I break off a piece of a geranium (Pelargonium), either by pruning or by accident I hate to throw out those sources of potential new plants. (It’s the thrifty in me.) To give a fresh cutting its best start you need to do something counter-intuitive to get it started: letting it dry out. Not the leaves, but the cut end of the stem.

Propagating plants is one of the most exciting and satisfying things about gardening. You are actually making a clone when you use vegetative propagation to make a new plant, so you can feel a little bit like a scientist while you do it. Here’s what’s really happening to that plant leaf or stem once it’s severed, from the blog Mastering Horticulture:

Plant parts such as leaves, when forcibly detached from the mother plant, undergo stress.  The natural response for such plant parts (just like in other life forms) is to start healing.   The first step in the healing process is the formation of soft protective tissue, known as callus, to cover the cut or wound.  Callus is characterized by a thickened outer tissue which is brought about by the rapid formation of undifferentiated mass of cells.

That’s the first part of the process, and a necessary part that allows a severed piece of plant to go on living, and breathing. Your cutting is a little like Frankenstein’s montster at this point. Then,

 Cells begin to respond to chemical, hormonal, and physical factors which trigger differentiation.   Differentiation is the process wherein new cells take on new and identifiable form and role.  Instead of continuing to grow and clump with the callus, new cells begin to be different.

The cells have become able to grow as roots. It’s quite magical. Now you have the beginning of a new plant. In the case of an African Violet leaf cutting, some of the cells in the callus also begin to differentiate into tiny new leaves, eventually creating an entirely new plant. And all you start with is one leaf. Not bad, eh? As soon as the differentiated cell tissues start to grow, they look like what they are becoming right away. Leaf shoot buds grow upward and are green, (and fuzzy, in the case of African violets) and roots are white and grow down. Remarkable really. And it all starts with a callus, the way a plant heals itself.

Tips to help your plant after cutting while it forms a callus:

  • put top part of cutting (the part with leaves) in plastic bag with stem ends left out in the air
  • zip-lock bag works well for this
  • cut holes for stems and stick out the bottom
  • piece of moistened paper towel inside bag keeps leaves hydrated while stem is drying and forming callus
  • leave bag in bright, but not direct sunlight, for 24 hours
  • then put stem or leaf cutting in water or damp soilless mix

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