01 Feb Replacing The Swiss Cheese in Your Garden
Over the past couple of years, there has been an influx of pathogens and insects setting their sights on destroying your garden spaces. Starting with Hemlock Woolly Adelgid, there has been Impatiens Downy Mildew, Basil Downy Mildew, Sudden Oak Death (SOD), Emerald Ash Borer, Boxwood Blight and most recently Spotted Lanternfly. And there has been one disease that has caused considerable foliage damage to one of New Jersey’s most popular foundation plants. Common cherry laurel or English laurel has long been susceptible to “Shot-hole disease, a combination bacterial infection (Xanthomonas prunii) and fungal disease (Blumeriella gaapi)” https://ugaurbanag.com/shot-hole-disease/. And while there are other bacteria, fungi and abiotic stresses that can attack cherry laurel, it is Shot-hole that creates circular holes in the leaves, eventually joining to make even larger holes. The leaves can look “like a shotgun was aimed at the plant” (Manual of Woody Landscape Plants 5th Edition). It is these holes that have been likened to that of Swiss cheese. Leaves which appear to be eaten away by disease, a ragged and certainly unkempt appearance remains. Well, fortunately for gardeners today, improvements have been made and more resistant varieties are now available. Great news, and just in time, as boxwoods will be fading fast from New Jersey residential landscapes leaving a vacancy for the next best evergreen to set against your homes’ foundation.
Cherry laurel are popular in New Jersey landscapes because they are an evergreen that flowers. Bold plants with lustrous dark green leaves, English laurel also flower white in April and May. Flowers that are roughly 3-5 inches long with nearly inch-wide racemes. However, some find their scent offensive as they dwindle down. Incidentally, the genus name from Latin means plum or cherry tree. The specific epithet means laurel cherry and refers to its laurel-like evergreen leaves and cherry-like fruit. With nearly 30 cultivars listed today, the two most popular in my nearly 30 years of retail experience are ‘Otto Luyken’ laurel, ‘Prunus laurocerasus ‘Otto Luyken’ and Schipka or Skip laurel, Prunus laurocerasus ‘Schipkaensis’. ‘Otto Luyken’ has a compact habit that seems to do well in sun or shade. Perfect for foundations, ‘Otto Luyken’ grows 3-4 feet tall and about 6-8 feet wide. A German introduction by Hesse Nurseries in 1968, this cultivar has been around most neighborhoods for quite some time. Schipka laurel, many don’t know, is a form found in 1889 near the Shipka pass in Bulgaria. Many landscapers and homeowners use this form against a home’s foundation only to find that it quickly grows 8-10 feet tall and 4-6 feet wide. Both cultivars, while widely popular, are susceptible to Shot-hole. Alas, there are some new cultivars resistant to this problem, maintaining similar structure in your garden.
‘Chestnut Hill’ cherry laurel, Prunus laurocerasus ‘Chestnut Hill’, is an improved selection to replace ‘Otto Luyken.’ More compact, also with glossy foliage, this selection has a refined look on what appears to be a vase-shaped form. Stalks of fragrant white flowers appear in the spring and this cultivar is suitable for foundations as well as a low hedge. Additionally, its projected growth, while similar in height to ‘Otto Luyken,’ is only about half its width. Hardy to Zone 6, ‘Chestnut Hill’ should also prove useful in urban gardens, mass planting and coastal exposures. All this and showy black drupes (fruit) are evident mid to late summer lasting into the fall. ‘Jade Enchantress’, Prunus laurocerasus ‘Jade Enchantress’, is another cultivar akin to ‘Chestnut Hill.’ Similar hardiness, height and attractiveness to birds for winter shelter, the only noticeable difference, I see, is that the overall structure of ‘Jade Enchantress’ is slightly smaller. It too, seems to possess improved disease resistance. ‘Majestic Jade’, Prunus laurocerasus ‘Majestic Jade’, should replace Skip laurel. A selection from renowned horticulturalist Michael Dirr and part of the Gardener’s Confidence Collection®, ‘Majestic Jade’ grows 6-8 feet tall and 5-6 feet wide. Lustrous dark green leaves, this cultivar’s improved disease resistance is an ideal selection for a natural or clipped evergreen hedge.
Camellia, privet, hydrangea and ivy are also susceptible to Shot-hole. Sanitation seems to be the best way to control the disease and keep it at bay. Clean up contaminated leaves from under the plant and spray with an “over the counter” fungicide if you are not ready to replace your existing laurels. Avoiding cleanup of infected leaves only contributes to the problem, as rain and watering can perpetuate the problem forcing the disease back to the plant by splashing. Useful tricks for growing cherry laurel successfully include; avoid heavy soils and standing water, prune immediately after flowering, avoid excessive fertilization and overhead watering. In the end, new cultivars are available today to rid your landscape of the Swiss cheese in your garden.