Authors

David A. Francko

Hardy palm expert David A. Francko has recently been a featured guest on such influential American programmes as Martha Stewart Living TV and National Public Radio’s Science Friday. Francko is chair of the Department of Botany at Miami University in Ohio and his academic specialty is aquatic plants. He is co-investigator on the university’s Hardy Palm Project, and for many years he has experimented with warm-climate plants in his own gardens. Francko’s findings have been published in scientific journals and presented at national and international conferences. As part of a network of adventurous gardeners living in cooler regions of the world, Francko refuses to accept the all-too-common belief that "palms won’t grow here".

Timber Press: How much trial and error did it take before you could reliably understand the microclimates of a landscape? Is it something that you still get wrong on occasion?

Dave: The tricky (and hard to quantify) thing about microclimates is that several factors enter into the overall equation — temperature, wind exposure, sun, and soil type to name the most important. It's not crucial that you get it EXACTLY right, just that you take advantage of your site's advantages! And yes, because it's complex I still get it wrong sometimes. The key thing is to take some measurements and do some observations and THEN plan your garden. Exactly how much of a temperature gradient occurs on your property during the coldest cold winter nights? How do these temperatures in your yard compare with published figures for your area for those same dates — are you colder or warmer and by about how much on average? Feel the force of the winter wind on your face to determine whether your house or other structures on your property act as effective windbreaks.

TP: What factor(s) most notably influence microclimates?

Dave: No question that proximity to structures that block wind and release some heat is the key thing, as well as the density of these structures around your immediate landscape. On the coldest nights, when the air is dead calm, the ground is covered with snow, and the sky is devoid of any cloud cover, the temperatures in a rural home garden can easily be 8 to 10 degrees F colder that those just a few miles away in a more urbanized (or suburbanized!) setting! It doesn't take a huge city to cause this effect.

TP: What would you say is the most that a person can stretch his or her USDA zone through the utilization of microclimates? Is a 3-zone change unrealistic?

Dave: I think, realistically, that there is about a 1 to 1.5 zone variation within any given geographical area based on typical ranges of microclimates (see above: strictly rural site with no heat island effect to site within a large city). Thus, the temperatures in my rural yard away from my house reflect the Zone 6a average of our broad region on their USDA map. Areas near my house are a couple of degrees warmer than that, and folks living just a mile away from me in a high density, urbanized housing development are gardening in yards that are effectively in "Zone 6b" or even borderline 7a rather than 6a.

Understand however, that this NOT to say that one typically finds ranges of 1 — 1.5 zone equivalents within a single property, although I suppose that's possible. More typically the range is a few to perhaps several degrees in minimum winter temperatures within a single garden site. Then, with attention to winter care (heavy mulching, antidessicant sprays), you can, in effect, add perhaps the equivalent of another 1/2 zone.

So, 3 zones is not possible, I think, without active and somewhat extensive winter protection (enclosures, supplemental heating, etc). However, "extensive" is best defined by each individual. This winter, I was able to overwinter largely intact foliage in a Chinese windmill palm with about 2 feet of trunk that I planted in my Zone 6a front yard just this past summer, even though air temperatures went down to -13 F. All I needed to do was cover the foliage loosely with holiday mini-lights, and then throw a couple of sheets over the plant on the three nights when temperatures went to zero or below. It stayed more than 25 degrees warmer under the sheets than in the air outside. Although I wouldn't want to mess with 10 plants this way, the few seconds it took me to protect this single palm was, in my view, well worth it!

TP: What about bending conventional wisdom in other ways? How do you feel about growing cool-climate plants in warm places, or desert plants in a rainy climate such as in the Pacific Northwest?

Dave: Absolutely! I believe people should grow, or try to grow, plants that interest them! After all, many people living in South Florida love to try to grow apples and other such fruits "better suited" to cooler climes!

TP: What is a favorite plant that you grow in your own garden?

Dave: I don't have a single favorite plant. I think the southern magnolia is my favorite evergreen tree, the crape myrtle my favorite deciduous tree or shrub, and the banana my favorite herbaceous perennial. And I like any and all palms because they truly are in a class by themselves!

TP: Which palm would you recommend for a novice gardener in a cooler climate who wants to add something unique to his/her garden, yet still lacks the experience you have in determining microclimates? In other words, which palm would the easiest for a beginner to grow?

Dave: No question, the needle palm (Rhapidophyllum hystrix) is the first choice for the novice, whether you're in Zone 7 or Zone 5, as long as you are in an area with warm to hot summers. Needle palms don't thrive in areas with cool marine climates unless care is taken to maximize sun exposure and heat gain during the growing season. Needle palm foliage is every bit as cold hardy as most boxwoods and hollies, and it's very forgiving as to soil type and sun/shade exposure. Besides, I also think it's a truly beautiful plant that integrates well with virtually any landscaping style. About the only downside is that during its first few years in the ground the spear leaves and bud tissue can be damaged even if temperatures don't do below zero, so mulch the base well with leaves and use antifungal sprays in the crowns.

Now, some might advocate that novices start with a dwarf palmetto (Sabal minor) in cooler areas, especially in marine climate areas with cooler summers. The bud tissue is below ground and is almost NEVER damaged by winter cold if the plant is mulched. The foliage is several degrees less cold hardy that that of the needle palm, but in areas that don't get much below zero F this is not an issue. And, in really cold areas, the underground bud tissue almost ensures plant survival and recovery even extreme temperatures kill all aboveground tissue. Actually — - the real answer is that I'd advocate a novice to try a couple of BOTH, and see which does better in their specific area.