Rockwool cubes

CoMo Grow Supply co-owner Thomas King recommends using Rockwool cubes to clone plants.

The arrival of spring means houseplant season is in full swing. For someone with a sizable plant collection, the urge to buy more can be strong. But through the process of propagation by cutting, also known as plant cloning, at-home horticulturists can multiply their plant collection with the help of the ones they have already grown.

Vox talked with CoMo Grow Supply owners Thomas King and Heather Yu for tips on how to best grow new plants through cuttings.

Step 1: Choose a plant

The most important step in the process is deciding what to grow. “I have had really good luck with peppers and tomatoes,” King says. He recommends starting with a plant that has a thin stem and substantial top foliage. Other types of plants King recommends for cloning are cacti, melons, peas, squash and succulents.

Step 2: Make the cuts

King says the approximate length of cuts should be between 4 to 8 inches, depending on the type of plant. Most plants are closer to the 7 to 8 inch range. Then, remove nodes and branches from the lower half of the plant using clean scissors or a fresh razor. Once the bottom half is trimmed, use a razor to scratch any remaining bark or exterior plant layer from the stem.

The final cut, except for when you're using succulents, is to the leaves, which King says is a small clip to the tips. “After you’ve gotten your branch cleaned up, it should look like a small tree, essentially like a little Truffula tree,” King says.

Ensure tools are clean and that you wear gloves for this step. The oils from human skin can clog the pores of the plant, and the plant will not root in places it made contact with skin.

Succulent cutting

Succulents are among the best plants to grow through cuttings.

Step 3: Plant it

Dip the bottom inch of the cutting into a root inoculant, which encourages the plant to root. Then, gently plant the branch into the soil medium. King says planting can occur in soil or rooting cubes such as coco cubes or Rockwool cubes, which are King’s preference for plant cloning. Rooting cubes should be soaked in a vegetative nutrient solution for 5 to 10 minutes before adding the plant, King says, so the plant will be fed for the first couple of weeks.

Step 4: Humidify

King recommends using a clone humidity dome, a clear plastic dome with a 10- to 20-inch tray, to keep the plant at 90% humidity while it grows.

Step 5: Grow and relocate

Once planted, the branch can take anywhere from 5 to 14 days to show roots. “Once the roots have completely perforated the growing medium or stick out like little chandeliers or like octopus roots, you can transplant it into a larger container,” King says. Other containers could include a cup full of soil with coco and perlite or a gallon pot.

What to avoid

King says a common mistake is taking a plant outside before the hardening process is complete. “Usually clones take one to two weeks to start tapping roots regardless of what medium you’re using,” King says. At this point, the stem is not sturdy enough to thrive outdoors. Once it reaches an ideal thickness of 2 to 4 inches, the plant is ready for a larger container. King says that when the plant reaches 12 to 18 inches tall, it is ready to start spending a handful of hours a day in outdoor lighting. The process will gradually acclimate the plant to life outside.

Treated soils are unhealthy for growing plants from cutting, Yu says. Cuttings struggle to root in soil that is oversaturated with nutrients, such a s Miracle-Gro. Yu also says to remember to change water every few days to avoid attracting mosquitos.

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