Green Giant Arborvitae (Thuja ‘Green Giant’) is a favored evergreen known for its rapid growth and dense, conical foliage. It is versatile for creating privacy screens, hedges, or windbreaks. Propagating these plants offers a cost-effective way to expand your garden by yielding new specimens from an existing plant.
Choosing the Right Time and Method
Propagating Green Giant Arborvitae from cuttings is most successful from late summer through early fall. During this period, the plant’s growth matures, producing semi-hardwood stems ideal for rooting. Taking cuttings then allows young plants to establish a robust root system before winter dormancy, improving their survival chances. This timing aligns with the plant’s natural growth cycle.
Cuttings are the most effective and common propagation technique, ensuring new plants are genetically identical to the parent. This guarantees desirable characteristics like rapid growth and disease resistance are reproduced. While seed propagation is an alternative, it is less common for home gardeners. Growing from seed can result in genetic variability, meaning new plants may not exhibit the same traits as the parent, and growth is often slower.
Gathering Your Propagation Supplies
You will need a pair of sharp pruning shears or a clean knife for precise cuts, preventing damage to the parent plant and cutting. Rooting hormone, in powder or liquid form, encourages root development by stimulating cellular growth at the cut end. A suitable rooting medium, such as perlite and peat moss or coarse sand, provides excellent drainage, aeration, and moisture retention.
Propagation trays or individual pots with drainage holes are needed for the medium and cuttings. Clear plastic domes or large clear plastic bags maintain high humidity, beneficial for rooting. Labels are helpful for identifying the date cuttings were taken, useful for tracking progress.
Step-by-Step Propagation by Cuttings
Select healthy, vigorous semi-hardwood stems from the current year’s growth on a mature Green Giant Arborvitae. These stems should be 6 to 8 inches long, with slight flexibility but firm texture. When cutting, include a small piece of older wood, called a “heel,” at the base. This heel contains dormant cells that promote root formation.
Remove needles from the bottom 2 to 3 inches of each stem to prevent rotting in the rooting medium. Gently score the bark at the base with a clean knife or fingernail; this exposes cambium tissue for better hormone absorption. Dip the cut end into rooting hormone, ensuring even coverage and tapping off excess powder.
Create small holes in your pre-moistened rooting medium with a pencil. These pilot holes prevent hormone from rubbing off. Carefully place each treated cutting into a hole, ensuring the bottom 2 to 3 inches are fully submerged. Gently firm the medium around the base for good contact.
After planting, thoroughly water until drainage occurs, settling the medium and providing hydration. Place the tray or pots in bright, indirect light, avoiding direct sun. Cover with a clear plastic dome or bag to maintain high humidity for rooting.
Caring for Your Rooted Cuttings
Maintain a consistent environment for root development. Humidity is important, so regularly mist the cuttings or ensure the humidity dome remains sealed to prevent desiccation. Keep the rooting medium consistently moist but not waterlogged, as excessive moisture can lead to rot and fungal diseases. Check moisture daily and water as needed.
Cuttings require adequate indirect light for photosynthesis, such as near a bright window or under grow lights, shielded from intense rays. Protect cuttings from extreme temperature fluctuations; stable temperatures between 65-75°F (18-24°C) promote root formation. Signs of successful rooting include new foliage or resistance when gently tugging the cutting, indicating root anchorage.
Transplanting and Long-Term Care
Once Green Giant Arborvitae cuttings have developed a sufficient root system (after several months), they are ready for transplanting. Before moving them, “harden off” the young plants by gradually exposing them to outdoor conditions over 7 to 14 days, increasing their time outside daily. This acclimation prepares them for the external environment.
Carefully remove each rooted cutting from the propagation tray, avoiding damage to delicate new roots. They can be moved into larger individual pots (e.g., 1-gallon size) or directly into a garden spot if roots are well-established. After transplanting, provide consistent watering, especially during dry periods, to help them settle. Protecting them from harsh winds or intense afternoon sun during their first few weeks post-transplant aids establishment. Light fertilization can be introduced after the first year to support continued development.