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Growing Culture

A Visit to Dark Heart




All images © Ed Rosenthal.

I recently visited one of the most respected cloneries in Northern California—Dark Heart Nursery. Through stores and dispensaries, it supplies both hobbyists and commercial enterprises with thousands of clones each week.

Dark Heart has a bank of plant varieties that it holds in tissue culture, which is a form of maintaining plants as cells in an undifferentiated form. Think of these as stem cells that can be regenerated to whole plants. This serves several purposes:

It takes little room. A library can be stored in a single refrigerator rather than in hundreds or thousands of square footage, and they require little care while in storage. The process also creates sterile material—no bacteria, fungi, pests or disease are present.

The technicians at Dark Heart regenerate plants from the tissue culture material to use as mother plants. These plants are usually grown to a height of three to six feet and are cut as they grow to force branching to get the plant to produce more clone material. They are grown in a sterile potting mix that contains peat moss and perlite, in 10-gallon containers.

Cuttings from these plants are the end product of the clone center. Groups of the cuttings are cut and placed in a beaker filled with a root growth enhancer containing a plant hormone such as Indole 3 Butyric Acid (more commonly known as IBA).

Each clone is trimmed down to just a few top leaves with pruned fingers. They are placed in two-foot rockwool cubes, 50 to each 10-foot x 20-foot tray, which have a grate bottom to promote drainage and air flow. A clear plastic dome is placed over the tray for the first few days. Within a few days, the cuttings have adjusted and the covers are removed. They are ready for sale when new growth has started in the canopy and roots appear at the bottom of the cubes.

The nursery also sells adolescent plants that are two feet tall with a bit of branching. Both greenhouse and outdoor growers buy these plants to get a head start on the season outdoors, resulting in considerably larger plants or to get faster turnover in greenhouses. Growing a crop from clone to ripening can take 90-120 days. However, without having to vegetate much, the time is cut down to 60-70 days.

Dark Heart has served the cannabis community of Northern California (and the rest of the world) for more than 15 years. It has succeeded because it consistently delivers high-quality, healthy and uninfected clones of popular varieties. Its products have helped growers of every size to produce bountiful, potent harvests.


In the foreground the sativa hybrid plants have been cut. Plants in the back, about six-feet tall are waiting for their “haircut.”

Cuttings are clipped, manicured, pruned, and placed in two-foot rockwool cubes.

On the left clones are maturing. On the right, new cuttings (in domes) are starting their two-week journey. Soon after that they will be adopted by expectant growers.

A sativa clone mother is about to be sheared for cuttings. These plants have life expectancy of about six months before they are replaced.

Rooted clones ready to find new homes.




Start planting now! Plant clones or germinate seeds so you can set the plants out as soon as the climate in your area permits. Remember the plants have to be kept in a vegetative state. You can do that by flashing lights on the plants several times each night for a few seconds using a bright led flashlight (preferably red) to interrupt the darkness. If you place them out early in the season (before March 15) you can keep them growing vegetatively using the light. Without the light, with the short days of spring, they will start to flower when set outside.