Thuja Green Giant is a popular evergreen choice for creating dense privacy screens and hedges due to its rapid growth. Propagating these trees from cuttings is a cost-effective way to expand your collection, producing new plants identical to the parent.
Understanding Thuja Green Giant Propagation
Propagating Thuja Green Giant from cuttings is the most common method for home gardeners. Unlike growing from seeds, which can lead to variations, cuttings produce clones that will grow to be identical to the tree they were taken from. This ensures the new plants will have the same growth habit, disease resistance, and foliage color.
The best time to take cuttings is late summer to early fall, when the current year’s growth is semi-hardwood. At this stage, the plant is actively growing, and stems are firm enough for successful rooting. While hardwood cuttings can also root, semi-hardwood cuttings show higher rooting percentages and better root quality.
Taking and Preparing Cuttings
Select healthy, disease-free branches from the current year’s growth, 6 to 8 inches long. Use clean, sharp pruning shears to make a precise cut just below a node. Some propagators prefer “heel” cuttings, which include a small piece of the older stem, as this can enhance rooting.
After taking cuttings, remove foliage from the lower one-third to one-half to prevent moisture loss and reduce the risk of rot. Lightly roughing up or making small vertical cuts on the bark at the cut end exposes more cambium tissue, which aids in root development. Applying a rooting hormone is highly recommended to stimulate root growth and quick establishment. Solutions of indolebutyric acid (IBA) between 3000 to 6000 ppm (0.3% to 0.6%) are optimal for promoting root number and length.
Planting and Caring for Cuttings
The rooting medium for Thuja Green Giant cuttings should be well-draining yet moisture-retentive. A common mix is equal parts perlite and peat moss. Coco coir can substitute for peat moss, and vermiculite or coarse sand for perlite. This mixture ensures aeration, preventing waterlogged conditions and rot. Thoroughly moisten the medium before planting.
To plant, create holes in the medium with a stick or dowel to avoid scraping off rooting hormone. Insert each cutting deep enough to bury the leafless portion. Space them adequately for air circulation and to prevent overcrowding. Keep the medium consistently moist but not saturated. Overwatering causes fungal diseases and rot, while insufficient moisture dries out cuttings.
Maintain high humidity around cuttings, using a clear plastic dome, bag, or mini-greenhouse. Regular misting also helps. The temperature range for rooting is 70-75°F (21-24°C). Provide indirect sunlight; direct sun can scorch tender cuttings. Rooting takes 8 to 12 weeks. Signs of success include new foliage growth or resistance when gently tugging.
Transplanting Rooted Cuttings
Once Thuja Green Giant cuttings develop a robust root system (after 8 to 12 weeks), they are ready for transplanting. Carefully move them from the rooting medium into individual pots or a nursery bed, handling delicate new roots with care to minimize damage. A potting mix for young plants should be well-draining yet moisture-retentive, similar to their preferred landscape soil. A mix of potting soil, organic compost, peat moss, and perlite or coarse sand is recommended.
Before permanent outdoor planting, harden off young plants. This gradual process acclimates them to outdoor conditions like varying temperatures, direct sunlight, and wind, preventing shock. Begin by exposing them outdoors for a few hours daily, gradually increasing duration over one to two weeks. After hardening off, plant them in their final location, ensuring the site has well-drained soil and at least four hours of direct sunlight daily.
Common Propagation Challenges
Challenges can arise during Thuja Green Giant propagation. Failure to root is a common problem, often due to incorrect timing (material too soft or woody). Insufficient humidity can cause cuttings to dry out before roots form. Using poor quality material, such as unhealthy or diseased branches, also reduces success.
Fungal diseases and rot are frequent challenges, often from overwatering or inadequate air circulation. Saturated medium creates an anaerobic environment, encouraging harmful pathogens. To mitigate, ensure the medium drains well and avoid excessive watering. Good air movement, through natural ventilation or small fans, helps prevent fungal problems. If cuttings turn brown or wilt, it indicates overwatering, underwatering, or extreme temperatures, requiring care adjustment.