How To Grow Heucherella
Heucherella is a fairly new genus made by crossing heuchera (Coral Bells) with tiarella (Foamflower), both North American native plants. The early crosses were made using fairly bland species, but current breeding incorporates new genetics like exciting, colored-foliage heuchera and superior tiarellas with unusual cut leaves and dark centers.
The first colored-foliage heucherella appeared in 2002 with ‘Sunspot’ and has been eclipsed by the introduction of new hybrids with Heuchera villosa in their background. This cross brings more heat and humidity tolerance and larger foliage to the plant, as seen in the cultivars ‘Sweet Tea’ and ‘Alabama Sunrise.’ We now revel in a rainbow of new foliage colors and most recently, trailing forms that are finding uses as colorful groundcovers in semi-shade or in hanging baskets. Never before has a hardy groundcover been available in such a range of foliage colors.
Terra Nova Nurseries has been at the forefront of breeding these beauties while being careful to add heat and humidity tolerance to plants that have nice habits and clean flowers on short spikes. Terra Nova currently offers 22 different heucherella (the world’s largest selection) in a mixture of different habits. Reports from heat trials as brutal as the summers suffered in Tulsa, Okla., Starkville, Miss., and Dallas, Texas, have seen these plants flourish. ‘Buttered Rum’ and ‘Gold Zebra’ were standouts in the Mississippi State and Dallas Arboretum Trials in 2013.
Growing And Using Heucherella
Heucherellas are essentially shade groundcovers. Pink to creamy-white flowers are put forth from mid-spring (May here in Oregon) to early summer with intermittent bloom into fall. They are relatively drought-tolerant, but appreciate occasional watering in summer. Even a desiccated plant will surprise you by perking up soon after a watering. In fact, the best way to kill a heucherella is to overwater it or plant it in clay soil. The importance of drainage is paramount to happy plants! (This goes for heuchera and tiarella, as well).
Foliage varies greatly between cultivars, but there is a good enough selection to work with many other plants in a combination planting. Do note that the height some varieties top out at is 10 inches and some can get up to 22 inches, so pay attention to the description on the tag or in the catalog. Spread also varies from 12 inches for heucherella ‘Dayglow Pink’ to 30 inches for heucherella ‘Kimono’ (or more for the groundcovers, which can get to 36 inches across in a season). We mulch our beds yearly with a one-inch layer of bark dust; taking care that the crowns of the plants are not buried deeply (another way to kill them). They are evergreen in milder climates.
We feel that heucherellas are front- and-center border plants, excellent near pathways and amongst the ferns and woodlanders. They are equally at home in a rock garden, tolerating much more sun than you might imagine, but they do prefer afternoon shade if possible. Forms like ‘Kimono,’ ‘Alabama Sunrise’ and ‘Sweet Tea’ are large enough that they can stand alone as a specimen or fill a container independently. Flower-power plants like ‘Honey Rose’ can make quite an impact when planted in large masses.
Heucherella Culture Tips
Heucherella are wonderful plants in containers, providing the services of both a spiller and filler, while not overwhelming other varieties. Silver-leaved forms like heucherella ‘Twilight’ make a perfect foil for bright-flowered annuals. Despite being from a wide range of genetic backgrounds, the culture of these plants is fairly basic and similar.
Media: Heucherella prefers a well-drained media as drainage is absolutely essential to this genus and high-peat mixes can drown this plant.
Planting: Plant one 72-cell liner per 4-inch quart or one-gallon pot and two or three liners per pot for larger sizes. Make sure to plant the liner evenly with the final depth of soil in the pot, as these plants are quickly killed by burying the crown.
pH/EC: These plants prefer a media pH of 5.5 to 6.5 and an EC of 0.75 to 1.25 via the pour-through method.
Temperature: A 50˚F to 55˚F nighttime air temperature and a 60˚F to 65˚F daytime air temperature are ideal for heucherella. Root temperature is also very important for success with 55˚F to 60˚F being ideal. Be careful to avoid excessive root temperatures as roots can be damaged quickly during the summer, especially in black pots.
Light: Most heucherella prefer filtered light and do best under 30 to 50 percent shade, depending on location. Some of the darker-leaved varieties like ‘Twilight’ perform well in full sun if the plant is well-established and has adequate irrigation. ‘Brass Lantern,’ ‘Buttered Rum,’ ‘Cracked Ice,’ ‘Solar Eclipse’ and ‘Sweet Tea’ are clumping varieties that also do well in full sun in the trials at the Denver Botanic Garden. Trailing varieties recommended for full sun are ‘Copper Cascade’ and ‘Redstone Falls.’
Fertilizer/Watering: Supply plants with a low rate of constant liquid feed of 17-5-17 or 20-10-20 at 50 to 75 ppm nitrogen. Too much nitrogen will cause lush, soft growth that is more susceptible to disease. Keep the growing medium evenly moist during production as roots are damaged by excessively dry conditions.
If plants are allowed to wilt badly, a preventative fungicide application is advisable, as root-rot pathogens are quick to colonize damaged roots.
Pinch/PGRs: Neither pinching nor PGRs are required to grow heucherella. The trailing varieties may be cut back if they get overgrown or intertwined with their neighbors.
Pests/Disease: While rust is problematic in some heuchera, all heucherella seem to be highly resistant to the disease. However, bacterial spotting and root-rot pathogens are associated with heucherella. Avoid overhead watering to prevent bacterial spotting. The beneficial bacteria Bacillus subtilis can prevent spotting, but copper fungicides are best for cleaning up an active outbreak. Keeping the soil evenly moist and at the proper temperature will prevent most root pathogens but broad-spectrum fungicides like thiophanate-methyl and etridiazole work well for correcting problems.
Relatively few pests affect heucherella; however, root weevils can be problematic. Notched leaves on nearby plants, especially rhododendrons, yews and hosta, are signs of their presence. Chemical control of weevil grubs can be achieved with a drench of acephate or a neonicotinoid. Adult weevils can be controlled by acephate and pyrethroid sprays; however, these applications are most successful when made during the evening as the beetles are nocturnal. Nematodes can also be effective, but make sure to follow the manufacturer’s irrigation instructions, as the proper application protocol is critical for success.
Some animal pests can be a problem. Deer and rabbits like eating the fresh new leaves and flowers but tend to leave the older leaves.
Scheduling: 72-cell liners work well in most containers, but 4-inch, quart and gallon sizes are most common. Growing a 72-cell to a 4-inch pot takes 4 to 6 weeks, a quart pot would take 5 to 7 weeks and a one-gallon pot would finish in 8 to 10 weeks.