Successfully Growing Brunnera Jack Frost

Susan Martin
Brunnera macrophylla Jack Frost has been selected as the 2012 Perennial Plant of the Year by the Perennial Plant Association. Introduced in 2000 by Walters Gardens, Inc., this hardy perennial has proven over the last decade to be a reliable, beautiful and popular perennial for shade gardens nationwide. It was first discovered as a non-induced mutation of Langtrees in the greenhouses at Walters Gardens, where it’s considered to be one of the very best introductions in their 65-year history.

Jack Frost has opened up all new possibilities for shade gardeners, giving them something new to complement the hostas, ferns and lungwort already in their gardens. Many retailers have reported that customers come in the store looking for hostas, but leave with a load of brunnera. It’s a woodland perennial that naturally prefers loose, organic, moist, but well-drained soil in the landscape. Its leaves are intricately detailed with a crackle-like silver finish and deep green veining, and their fuzzy texture makes it less favorable to deer and other pests. Tiny, baby blue, forget-me-not type blossoms are held above the foliage in spring.

Growers at Walters Gardens favor Jack Frost because it’s proven to be more heat tolerant than older cultivars and is a vigorous grower. There are three main keys to growing Jack Frost successfully: consistent moisture, shade and using a preventative fungicide drench when transplanting into containers. 

  • Moisture  Consistently moist, well-drained soil is essential. Don’t let this plant dry out, but don’t overwater it either. On a scale of 1 to 5, we water our plants well, dry them down to level 3, then water them again. Dry soil leads to scorched foliage, whereas wet soil invites root and crown rot. Roots should be tan to white in color. 
  • Shade  We grow our brunnera under 55% shade cloth, which is common in the industry. While they can handle short periods of sun if provided with adequate moisture, it’s tough to overshade these plants. Too much direct sun will cause them to burn. Brunnera fits easily into greenhouse production alongside hostas and other shade plants. 
  • Preventative fungicide drench  After transplanting plugs into larger containers, we recommend using a preventative fungicide drench of thiophanate methyl and etridiazole (commonly sold as Banrot). Since fungal diseases are difficult to treat, we prefer to work proactively with this preventative drench.
  • Growing media  Jack Frost grows well in a standard mix of bark, peat and perlite. As long as you use a loose, not heavy, mix that allows good drainage, you should have good success. We recommend a soil pH of 5.5 to 6.0 for plugs and 5.8 to 6.3 in containers.
  • Fertilizer/EC  Brunnera are not overly heavy feeders, especially at the rooting stage. We use a constant feed of 100 ppm N for plugs and 125 to 150 ppm N for containers. Using the pour-through method, we maintain an EC of 1.5 to 2.5 for plugs and 2.0 to 3.0 for containers. Growing these plants too lean will result in yellowing on the leaves.
  • Temperature  Growing Jack Frost cool and slow will result in the highest quality finished plants. However, it can also be pushed for spring sales. When rooting plants in spring, maintain a temperature of 65F (18C) and then drop to 55-65F (12-18C) to finish. When overwintering, don’t let the soil drop below 35F (1.6C), remove the foliage, and watch for botrytis. Vernalization isn’t necessary for flower production, but is beneficial.
  • Pest and disease issues  Applying a preventative fungicide drench when transplanting as well as maintaining a low pH will help to avoid potential diseases. Thielaviopsis, Phytophthora and Fusarium are potential issues with brunnera, especially if they’re stressed when growing. Aphids and slugs are the primary pests you’ll encounter and can be treated with typical controls.
  • Finishing  Brunnera can be finished in 1 to 2 gal. containers. When starting with a 72-ct plug, we recommend receiving them in the fall and finishing them in 1-gal. containers for spring sales. Larger 20-ct plugs can be received in fall or spring for spring sales. Twenty-ct plugs take approximately 6 to 8 weeks to finish in a true 1 gal. or 10 weeks to finish in a 2 gal. Be sure to moisten plugs and separate the roots of any rootbound plants before transplanting. Set the crown at soil level in the container. No PGRs are needed. GT

Susan Martin is the director of marketing communications for Walters Gardens, Inc. She can be reached at Walters Gardens growers who contributed to this article include: Cindy Reimink, Ken Morse, Lonette Lemberger and Jeremy Windemuller.