Arborvitae (Thuja) are popular evergreen conifers, often chosen for hedges and privacy screens due to their dense foliage and relatively fast growth. Propagating these plants from cuttings offers a cost-effective method to multiply existing specimens or acquire new ones. This technique ensures new plants are genetically identical to the parent, allowing gardeners to expand their landscape with desired varieties without significant expense.
Best Time and Method for Propagation
Propagating arborvitae from cuttings is the most effective method, as it produces plants true to type, meaning they will have the same characteristics as the parent. Unlike growing from seed, which can result in genetic variations, cuttings provide exact replicas. The optimal period for taking arborvitae cuttings is typically from late summer through early winter, particularly after the first hard frost but before deep freezes. This timing allows the cuttings to enter a dormant state, which can encourage callusing before active growth begins.
Other propagation methods, such as starting from seeds, are less common for home gardeners because they often lead to variable results and require a longer period to produce a mature plant. Cuttings generally root within a few weeks to several months, offering a much quicker path to establishing new plants. The ease of rooting arborvitae cuttings makes this method accessible for many gardeners.
Taking and Preparing Cuttings
Selecting healthy, disease-free parent plants is an important first step for successful propagation. Choose branches from the current season’s growth that are firm but pliable, typically 4 to 10 inches long. A “heel” cutting, which includes a small sliver of older wood from the main stem, is often recommended as it provides more surface area for root formation.
Once the cutting is taken, carefully remove the foliage from the bottom 1 to 2 inches of the stem to expose the nodes where roots will emerge. To further encourage rooting, gently wound the base of the cutting by lightly scraping a small section of the bark to expose the inner cambium layer. This wounding creates additional sites for root development.
Applying a rooting hormone to the prepared end of the cutting can significantly increase the chances of successful root formation. Powdered or liquid rooting hormones are commonly used. Dip the wounded end of the cutting into the rooting hormone, ensuring even coverage.
Planting and Caring for Cuttings
The choice of planting medium is essential for successful rooting, requiring a mix that retains moisture while providing excellent drainage. A common and effective rooting medium consists of a blend of peat moss (or coco coir) and perlite (or vermiculite).
Plant the prepared cuttings into pots or trays filled with the chosen rooting medium, ensuring the defoliated and hormone-treated portion of the stem is fully inserted. Space the cuttings adequately to allow for air circulation and root development. After planting, thoroughly water the medium to settle it around the cuttings. To maintain high humidity, cover the pots with a clear plastic dome or bag, preventing the cuttings from drying out.
Place the covered cuttings in an area that receives bright, indirect light, avoiding direct sunlight which can cause overheating and stress. An ideal temperature range for rooting is typically between 65°F and 75°F (18°C to 24°C). Consistently monitor the moisture level of the rooting medium, keeping it moist but never soggy. Bottom watering, by placing the pots in a tray of water, can help the medium wick up moisture as needed. Rooting typically occurs within 6 to 10 weeks, though it can take longer, especially for cuttings taken in winter.
Transplanting Your New Arborvitae
Determining when cuttings have successfully rooted is crucial before transplanting. Indicators include the emergence of new growth, resistance when gently tugged, or roots emerging from the drainage holes of the pot.
Before moving the rooted cuttings to their final outdoor location, it is important to harden them off. This gradual process acclimates the young plants to outdoor conditions, such as fluctuating temperatures, direct sunlight, and wind, preventing shock. Begin by placing them outdoors in a shaded, sheltered spot for a few hours each day, gradually increasing their exposure over one to two weeks.
Once hardened off, the rooted arborvitae can be transplanted into larger pots or directly into the garden. Early spring or fall are generally suitable times for transplanting.
When transplanting, dig a hole that is twice as wide as the root ball to allow for ample root spread. Gently remove the rooted cutting from its container, being careful not to disturb the delicate new roots. Place the plant in the prepared hole, ensuring the top of the root ball is level with the surrounding soil. Backfill with a well-draining soil mix, and water thoroughly to settle the soil around the roots. Continued consistent watering is important during the initial establishment period in their new location.
Common Propagation Challenges
Despite the relative ease of propagating arborvitae from cuttings, several challenges can arise. One common issue is the failure of cuttings to root, which can stem from incorrect moisture levels (too much water leading to rot or too little causing desiccation) or poor cutting selection. Ensuring proper rooting hormone application and consistent environmental conditions can help mitigate these problems.
Fungal diseases, such as damping-off, pose another threat, particularly in overly moist or poorly ventilated environments. This condition causes young seedlings or cuttings to rot at the soil line. Using sterile rooting medium and containers, maintaining good air circulation, and avoiding overwatering can prevent fungal issues. If signs of disease appear, removing affected cuttings promptly can prevent further spread.
Slow growth or lack of vigor in rooted cuttings can occur if they are not receiving adequate light or nutrients after rooting. Arborvitae prefer full sun to partial shade once established, and a balanced, slow-release fertilizer can support healthy growth in potted plants. Additionally, ensuring proper drainage in the potting medium and avoiding compacted soil are important for robust root development and overall plant health.