Pining for Mugo: A Maintenance Guide for Mugo Pines

Globally, mugo pine (Pinus mugo) is one of the most cultivated coniferous evergreen shrubs in the world. For decades, gardeners have used this classic and adaptable shrub in everything from contemporary gardens and rustic landscapes to avant-garde topiaries and zen bonsai. Even today, mugo pines continue to be a popular choice among gardeners and professionals alike due to their natural resilience to pests, as well as their versatility and functionality in the modern urban landscape.

Cultivation

Mugo pine’s forgiving nature makes them perfect for the novice gardener. They are a relatively low maintenance shrub with excellent cold hardiness, able to grow in Zones 2a to 7b. Mugo pines perform best in full sun, but will tolerate partial shade in cooler climates. They are also good candidates for dry, open sites due to their drought and wind tolerance. While these shrubs are not particular to any specific soil type, mugo pines should never be planted in heavy, wet soils. Similarly, the root system should be protected with a layer of plain, coarse-textured mulch. Like many plants, mugo pines can benefit from compost and other organic amendments, although they are not considered to be picky eaters and can readily survive with or without fertilizers. Spacing

On average, mugo pines grow to be relatively stout shrubs (5’ × 10’), but can exhibit a variety of forms including dwarf and standard. If it seems like your mugo pine is taking forever to fill out, don’t panic. Even with proper love and care, mugo pines exhibit a slow growth rate and can take upwards of 10–20 years to reach their full size at maturity. Ironically, though the specific epithet mugo means “small mountain pine”, these shrubs can sometimes grow quite large, up to 20’ tall and 30’ wide!

For gardens with restricted space, there are many true dwarf cultivars available such as ‘Mops’, ‘Slowmound’, ‘Gnome’, and ‘Sherwood Compact’. Dwarf mugo pines can also be grown in containers. When containerizing a mugo pine, choose a container that has drainage holes and is at least six inches in diameter larger than the root ball to allow for ample root growth. Use a high quality, porous media or substrate and ensure to adhere to a weekly irrigation schedule. Consider applying a slow-release granular fertilizer to your containerized shrub once a year, preferably in spring. Mugo pines can be transplanted into larger containers every 2 to 3 years, for up to 10 years. Thanks to their cold hardiness, all mugo pines can be left to harden off and overwinter outdoors.

Pruning

As a general rule, coniferous evergreens do not require regular pruning maintenance aside from the removal of diseased, damaged, dying, or dead branches. Gardeners should select a cultivar that will not outgrow its space and let the pine grow unassisted to preserve its natural beauty and aesthetics. It is important to note that imprudent “pruning-to-fit” can cause severe or permanent disfigurement in pines, since they cannot replace lost growth like their deciduous, broadleaf cousins. If a formal appearance is desired, then candling can be performed to achieve a more tidy, compact look.

Candling is a pruning technique where condensed stalks or buds of new terminal growth (“candles”) are selectively shortened or cut to reduce or restrict the growth of a pine tree. This process must be done while the candles are appressed and soft, before the needles unfurl and the shoot hardens in midsummer. If a terminal is candled too late, it will not form new buds for next year’s growth which will result in tip dieback. The best time to candle pines is in late spring, when current year’s needles are about half the length of previous year’s needles. To create a more symmetrical form, stagger candling based on shoot vigour:

• Begin pinching weaker areas first, removing no more than ⅓ of the total candle length.

• After 2–3 weeks, finish pinching the strongest areas by reducing candles by ½; vigorous areas can be reduced by ½ to ⅔.

• If your shrub is too sparse, only remove the primary candles (the stronger or taller buds).

• If your shrub is too dense, only remove the secondary candles (the weaker or shorter buds).

Pests & Diseases

Mugo pine is a very resilient shrub and rarely encounters issues with pestilence. Because of their aromatic resin, mugo pines are unpalatable to most grazers, including deer. However, they can be susceptible to a few insect pests such as redheaded pine sawfly (Neodiprion lecontei), pine needle scale (Chionaspis pinifoliae), and pine bark adelgid (Pineus strobi). For mild infestations of these pests, mechanical controls like handpicking, hose spraying, and pruning can be very effective. Severe, persistent, or recurring infestations can be managed with chemical controls like biorational products (e.g. insecticidal soaps, horticultural oils, etc.). Less common issues include pathogens such as tip and needle blights, root rots, and fungal diseases. In particular, Phytophthora is commonly observed in mugo pines that have been planted too deeply or improperly cared for in containers. The best strategy for managing these disorders is to maintain shrub vitality with good cultural practices (e.g. watering, fertilizing, mulching, pruning, aeration, etc.). Preventative treatment with fungicides like Bordeaux (1:1:100) can also be used, when necessary.

When in doubt, contact a professional to ensure your landscape can be enjoyed for years into the future. Contact us for a consultation today!