The green giant thuja remains a public domain conifer allowing anyone to grow a green giant from a cutting. To propagate the green giant from cuttings, gather clippings from the last summer's growth late in the winter. Cuttings taken earlier in the year do not do as well when trying to root them. Bottom heat aids in the development of the root system on the cuttings. The use of a rooting hormone speeds the root development as well.
Clip 6-inch sections of the green giant using the pruning shears or a sharp knife. You want the cuts to be clean and straight, not jagged, so the host thuja is not damaged.
Fill the growing tray with the soil mix and spray lightly with water. Dampen the soil but do not allow it to become soggy. Using a pencil or straw poke holes at even intervals in the soil for the cuttings.
Pour 2 tablespoons of the dry rooting hormone (most garden centers carry this in powder or liquid form) from the container into a paper cup or other container. This reduces the risk of contamination from plant diseases to the original bottle of compound.
Remove the lower leaves of the green giant cuttings leaving about 3 inches of the stem exposed. Dip the exposed stem into the paper cup with the rooting hormone and shake off any excess powder. Place the cuttings into the holes of the soil.
Tamp the soil into place around the green giant cuttings to eliminate any air pockets. Air pockets in the soil contain bacteria that damage cuttings. The cuttings will rot away instead of rooting.
Cover the green giant cuttings with plastic and place on the heat mat. Place the growing tray and heat mat in a bright location but out of direct sunlight. Open the plastic at least once daily during the growing period to ventilate the cuttings.
Check the cuttings at least once a week. Remove any cuttings showing signs of mold. Water the soil when it becomes dry to the touch but be careful about over watering as this will kill the cuttings quickly.
Wait 6 to 8 weeks for the green giant cuttings to develop a strong root system. Once the cuttings have established themselves, remove from the growing tray and pot up in larger pots. Plant the new trees outside in the spring when get warmer.