The North Pole Arborvitae (Thuja occidentalis ‘North Pole’) is a popular evergreen known for its distinctive narrow, upright growth habit, making it suitable for hedges, screens, or as a striking focal point in landscapes. While generally considered a hardy and low-maintenance plant, thriving across a range of USDA hardiness zones from 3 to 8, it can still experience specific issues that affect its health and appearance. Understanding these common problems can help maintain the plant’s lush green foliage and columnar form throughout the year.
Environmental and Cultural Issues
Environmental factors and improper care can significantly impact the health of North Pole Arborvitae. One common concern is winter burn, which causes foliage to brown, especially in exposed sites. Although the ‘North Pole’ cultivar is noted for its resistance to winter burn, severe cold winds and frozen ground can still prevent water uptake, leading to desiccation. Ensuring the plant is well-hydrated before winter and applying a thick layer of mulch around the root zone can help protect it.
Drought stress can also lead to browning and needle drop, particularly during prolonged dry periods. Consistent and deep watering is important, especially for young plants during their first growing season, to establish a robust root system. Once established, North Pole Arborvitae can tolerate some dryness but still requires watering during extended dry spells, generally about one inch of water per week.
Improper planting techniques contribute to various problems. Planting too deep can lead to root suffocation and rot, while planting too shallow might cause instability and expose roots to temperature fluctuations. The planting hole should be as deep as the root ball and twice as wide, ensuring the top of the root ball is level with the soil surface. Gently roughing up circling roots before planting can also promote proper root growth.
Poor soil drainage is another significant issue, as North Pole Arborvitae does not thrive in overly wet conditions. Waterlogged roots can lead to suffocation and root rot, even without the presence of a specific pathogen. Amending heavy clay soils with compost can improve drainage, and selecting a site with naturally well-draining soil is advisable.
Sun scald, though less frequently mentioned for ‘North Pole’ due to its hardiness, can still occur on young plants or during intense heat waves, particularly if the plant is not adequately hydrated. Providing some afternoon shade in hot climates can be beneficial. Protecting young plants with a windbreak in severe winter wind regions can also mitigate environmental stress.
Pest Infestations
North Pole Arborvitae can become susceptible to several insect pests, which can cause visible damage to its foliage. Identifying these pests early helps in implementing effective treatment strategies.
Arborvitae leafminers are one such pest, causing tunneling damage within the needles that results in browning tips. The larvae of these tiny whitish moths feed inside the foliage, leading to discoloration. Monitoring for their presence and applying appropriate treatments, if necessary, can help manage infestations.
Spider mites, tiny eight-legged creatures, can also infest arborvitae, especially during dry, dusty conditions. Their feeding results in a fine yellowish speckling or stippling on the foliage, eventually causing leaves to turn brown. To check for mites, tap a branch over a white piece of paper; if present, tiny specks will appear and crawl. Horticultural oils or insecticidal soaps can be effective treatments, but thorough coverage is important.
Bagworms are distinctive pests that create cone-shaped bags from silk and plant debris, causing defoliation as they feed on the foliage. These bags can be seen hanging from branches. For light infestations, hand-picking the bags, particularly during winter or early spring, can help control their population. For more severe cases, appropriate insecticides may be necessary.
Aphids can congregate on new growth and produce a sticky substance called honeydew. While generally considered relatively harmless unless in large numbers, their presence can attract sooty mold. A strong stream of water can dislodge aphids, or insecticidal soaps can be applied to manage larger populations.
Disease Challenges
North Pole Arborvitae can face various fungal or bacterial diseases, often exacerbated by environmental conditions. Understanding the symptoms and implementing timely management strategies is important for plant health.
Canker diseases manifest as sunken, discolored areas on branches, which may ooze sap and eventually lead to branch dieback. These cankers can girdle smaller stems, causing the portion beyond the canker to die. Pruning out infected branches, making cuts well below the diseased area, and maintaining overall plant vigor can help limit the spread of these diseases.
Root rot, specifically pathogen-induced forms like those caused by Phytophthora species, differs from issues caused solely by poor drainage. Symptoms include yellowing foliage, wilting, and eventual plant death, often occurring in overly wet soil conditions. The fungus thrives in anaerobic environments created by excessive moisture. Prevention is paramount, focusing on proper planting in well-drained soil and avoiding overwatering.
Tip blight, such as Phomopsis blight, causes browning and dieback of branch tips, which may progress inward. Young needles may develop yellowish spots, turning reddish-brown as they die. This fungal disease is often favored by wet, humid conditions. Management involves pruning affected areas during dry weather, sterilizing pruning tools, and improving air circulation around the plant. Avoiding overhead irrigation can also reduce the incidence of tip blights.
Prevention and Best Practices
Maintaining the health of North Pole Arborvitae largely depends on proactive measures and consistent care. Selecting an appropriate planting site is fundamental, choosing a location that provides full sun to partial shade, ideally at least six hours of direct sunlight daily. The soil should be well-draining, as arborvitae do not tolerate standing water.
Adequate watering is essential, particularly during the plant’s establishment period. Providing consistent moisture, especially during dry spells and before winter, helps prevent drought stress and winter burn. Checking soil moisture by hand can guide watering frequency, ensuring the top few inches are damp.
Applying a layer of mulch, about 2-3 inches deep, around the base of the plant helps retain soil moisture, regulate soil temperature, and suppress weeds. It is important to keep the mulch a few inches away from the trunk to prevent moisture buildup and potential rot.
Fertilization can promote plant vigor, with a general-purpose or slow-release fertilizer applied in early spring before new growth begins. Over-fertilization should be avoided, as it can harm the plant.
Pruning is generally minimal for North Pole Arborvitae, focusing on removing dead or diseased branches and light shaping in early spring or summer. Avoid heavy pruning or cutting into old wood, as this can hinder regrowth.
Regular inspection of the plants for early signs of pests or diseases is beneficial. This allows for timely intervention before problems become severe, protecting the overall health and aesthetic appeal of the North Pole Arborvitae.