Zone Envy

October 7, 2016 | Doug Oster comments

There are just a few beautiful dark-red blooms left on a crape myrtle shrub on display in the nursery area of Trax

Crape Myrtle

This is crape myrtle ‘Purple Cow,’ one of the last crape myrtles to still be in bloom at Trax Farms. PHOTO BY DOUG OSTER

Farms in Finleyville. It’s one of the most coveted plants for adventurous gardeners, who long for plants that aren’t supposed to thrive in northern climates.

Matthew Hirsh is a horticulturalist at the nursery and calls this phenomenon “zone envy.”

The USDA puts out a hardiness zone map that shows the average annual extreme minimum temperatures measured from 1976 through 2015. The zones are numbered from one to 13, with one being the coldest. Most of Western Pennsylvania is between five and six.

Perennials, shrubs and trees are labeled by their zone hardiness so gardeners know if the plant will survive in their zone. So why try to grow a Zone 6 plant if you live in Zone 5? Hirsh, who admittedly has zone envy, chuckles and answers, “Maybe it’s the challenge, maybe it’s having something in your yard no one else has.”

The crape myrtle is the No. 1 plant that like-minded gardeners ask for. Hirsh says the desire often comes from seeing the plant in its splendor while traveling. The trees are unique and striking in full bloom, causing many gardeners to fall in love at first sight.

He says his customers usually start with, “I was on vacation in the Outer Banks and they have crape myrtle. Can I grow these at home?” His answer is “yes and no.”

The key is identifying the microclimate in your yard and finding a place the plant can thrive. If a marginally hardy plant is put on top of a windy hill, it’s hit or miss.

“If you put it on the east or the south side of the house, where it’s getting the warmth from the house and missing the winter west wind, your chances are much, much better,” he says.

In the coldest winters, plants such as crape myrtle can be killed to the ground, but usually will return again the next season, sprouting from the roots. “Once you get past that first winter and get a little bit of woody growth built up, it gets a little tougher and more resilient,” he says.

Plant breeders are always working to make plants like these more cold tolerant. It makes sense, as zone envy sells plants and gives gardeners something special for their landscapes.

Monrovia offers three varieties bred for hardiness. Although it’s not that unusual to see a crape myrtle hardy to Zone 6, ‘Tonto, ‘Pecos’ and ‘Zuni’ were all released with hopes they could withstand a tough winter and not die to the ground.

“It seems like their new growth turns woodier faster than some other varieties, which I think is the key,” Hirsh says. “Lots of others are hardy to Zone 6, and with a little protection, I think they would have no problem around here.”

Crape myrtle can be grown as a shrub or tree, depending on the variety and how they are pruned. The stunning blooms can be pink, red, purple and even white. The plant will start blooming midsummer and last all the way through fall, which Hirsh says is a great way to add interest in the garden after spring.

“So many of the shrubs we use in our area are finished blooming by the time we get to midsummer,” he says. “So it’s a great addition for some summer color.”

Another plant that people see on vacation is the mimosa tree, prized for its pinkish, airy flowers. It’s also another plant that’s hardy to Zone 6. Hirsh has been growing one in his own yard.

“I confess, I did put this in the open to see what happens,” he says. “It does die back to the ground each year and regrow.”

With a little protection, though, he’s seen them grow to 20 feet in our climate. It’s a tree that’s both loved and hated in the South because it’s invasive, sprouts from the roots and throws seeds everywhere.

Another plant he loves to tell gardeners about is vitex, or chaste tree.

“It looks similar to a butterfly bush,” he says, “a little more of a true blue, definitely a cool plant.”

‘Blue Puffball’ stays compact, growing only 3 to 4 feet tall and wide. It’s a long bloomer, sending out deep-blue, aromatic flowers starting in June and continuing through September when grown in full sun. Hardy to Zone 6, it loves the heat, Hirsh says.

“It dies back a bit in the winter, but the stems usually do stay viable and greens right up in the spring,” he says.

Native Carolina allspice or sweetshrub (Calycanthus floridus) is cold hardy, but there’s a showier cultivar named ‘Aphrodite’ with large, fragrant bright-red magnolialike blooms. Reliably hardy to Zone 5, it doesn’t need the kind of protection some other plants do. It’s carefree and will bloom in a variety of lighting conditions in average garden soil.

These shrubs and trees are all planted as any hardy variety would be. Dig a hole twice as wide as the root ball, improve the soil where needed and be sure not to plant it deeper than it was grown in the container.

The best thing gardeners can do is provide plenty of water if rain is hard to come by. The plants should be watered until the ground freezes solid.

“Often, I’ll suggest the first year doing a little windbreak barrier with some weed fabric or burlap,” Hirsh says.

Even though most gardeners struggle with getting mophead hydrangeas (Hydrangea macrophylla) to bloom, he sells a variety for Zone 6 that’s different than most. “It’s a new borderline hydrangea called ‘Zorro.’ It has black stems and pure white flowers,” he says.

When asked why any gardener in their right mind would want to grow such a tender hydrangea, Hirsh says, “Maybe we’re gluttons for punishment.”

If you want to grow marginally hardy plants, Maria Zampini, president of horticultural marketing firm UpShoot and author of Garden-pedia, says, “Enjoy it while you have it. If you go into it willing and knowing this plant might not make it, you shouldn’t get upset if it dies.”

That mindset can make the challenges of growing zone-envy plants a lot easier. Zampini loves to experiment with plants and is trying out crape myrtle in her Zone 5 garden in Ohio. She is fine with the plant dying back to the ground and acting more like a perennial, “but I’m never going to have that beautiful exfoliating bark,” she says.

‘Deja Bloom’ azaleas are reblooming varieties, but the type she’s testing are hardy to Zone 6. She’s going to leave them in their pots and store them against her house. “I’m going to put them in a protected spot surrounded by bales of hay leftover from my Halloween display.” She might also add burlap around them, too.

She’s the fourth generation of her family to be in the nursery industry and has learned valuable lessons about what a difficult task it can be to grow any plant. Failure might not have anything to do with the gardener.

“Mother Nature is like the pitcher and you are the batter,” she says. “Every spring, you don’t know if she’s going to throw a spitter, slider or a curve ball.”