Vertical Gardening in Tennessee: What Actually Works in Our Heat and Humidity"
In Tennessee‚ the biggest issue in vertical gardening is combatting the heat and humidity of the summer sun․ Wall pockets or hanging containers that only have an inch or two of soil can bake dry after a day or so in the hot afternoon sun․ Systems that work well in a desert climate like Colorado or in a mild coastal climate will just not work here without some modification․ This section deals with the hardiness zones of Zones 6b and 7b where most of the state of Tennessee falls and what works there․
Why conventional vertical gardening tips may not apply here
Most books on vertical gardening consider their primary audience to be in the temperate climate․ In Tennessee‚ during the summer months‚ temperatures are around or above 90 degrees Fahrenheit with humidity levels of 70 to 80 percent․ It is quite likely that East Tennessee winter temperatures in the teens would present problems for the vertical gardener that would not be present for a horizontal gardener working at ground level․ The soil in a vertical planter could become very dry from wind and sunshine or very wet from a heavy summer rainstorm․ Fungal plant diseases may also be a problem for vertical planters mounted to walls․
I have seen felt pocket wall planters in August where the plants are rotting at the crown and the felt has turned into a layer of powdery mildew․ Again‚ the problem is that the pockets are staying too moist at the crown (in this humidity‚ anyway) and that's a breeding ground for fungal disease․ Wood or ceramic structures with drainage holes tend to work better than the fabric systems heavily marketed to northern gardening communities․
Best Vertical Garden Structures for Tennessee Growing Conditions
For durability‚ cedar or cypress trellises are superior to pressure-treated pine in our climate․ In humid summers and wet winters‚ rot resistance is a plus․ When considering your options‚ trellises against a south-facing wall will be baked in the hot afternoon sun; thus‚ plants grown on one require careful selection․
Metal or wooden tiered shelving can be used on Tennessee patios․ Open shelving allows air to circulate around pots to prevent mildew growth‚ which may result from watering pocket systems constructed from fabric․ On the other hand‚ the standing water from our frequent summer thunderstorms can rot the bottoms of wooden shelves and pots in a season or two․
In hanging baskets‚ the roots and soil should be checked more regularly for repotting‚ because the rain means the plants' roots and compost do not dry out․ You can stand and stare as much as you like‚ but the shallow roots then struggle in the week when there is no rain․
Plants That Actually Thrive in Tennessee Vertical Gardens
Skip the succulents‚ unless your vertical garden will live under an overhang․ They don't hold up to the humidity of Tennessee air (they're used to the arid climate of their native habitats‚ as you can see in the picture)․
Clematis are one of the better choices for a trellis in Tennessee․ Once established‚ clematis do very well in our heat․ They bloom from late spring to fall (depending on species)‚ tolerate wet soil and are not known for disease problems as some flowering vines are․ However‚ afternoon shade is recommended in Middle and West Tennessee‚ where summers are hotter than in East Tennessee mountains․
The native Christmas fern and autumn fern do very well in a vertical wall planter in partial shade‚ as long as the planter itself is oriented north or east‚ and gets a couple hours or less of direct midday sun․ These are the types of fern that grow naturally in our woodlands․ Several native ferns that are already acclimated to growing conditions in the Southeast mean TN Nursery plants already have an important advantage over those shipped from greenhouse growers elsewhere in the country․
Plus‚ English ivy and creeping fig will survive our winters without die-back in most of the state‚ providing a year-round wall cover‚ not a plant you have to replace every spring․
Hostas are usually not used in vertical gardens‚ but they can be used on tiered shelves in shaded areas‚ filling in space with big leaves‚ often before the end of the first season․ The humidity and rainfall in Tennessee are so favorable that hostas are used in Southern shade gardens․
Pole beans and cucumbers are also productive edible vertical garden plants in Tennessee․ In Middle Tennessee‚ the growing season is from mid-April to late October․ The growing season is slightly shorter in the eastern half of the state․ Peas grow well‚ but once it gets past 80‚ they bolt‚ and that's pretty much towards the end of May here․
Tennessee vertical garden construction timelines․
But once attached to a trellis‚ a clematis needs another full season‚ or two‚ before the new roots can provide enough support for all that heavy flowering․ Wall pockets are more accommodating․ In spring and fall‚ ferns filling in the wall grow into it in 6 to 8 weeks; in mid-summer they grow slower‚ and during winter they go semi-dormant unless you find a warm pocket in West Tennessee․
If you do choose to use nursery starts for your living wall‚ expect a full season before the wall looks as good as those you see on the web․
Watering: The True Challenge in Our Climate
Although it can rain in Tennessee and at other times there may be drought‚ the main issue is to regularly water․ A drip system with a timer is ideal․ Many people have learned how quickly wall soil dries out during a July drought‚ and how easy it is to overwater after a week of rain in Tennessee‚ if you have set up a watering regimen and don't bother to check the soil moisture content․ If the wall soil can be penetrated a finger's length or so and feels moist‚ do not water․
A Few Things Other Guides Miss
Systems installed directly against masonry walls such as brick or stone should also have a moisture barrier behind them because of the high humidity in Tennessee‚ where moisture can amass behind the masonry and work its way into the wall system causing mold․ It is possible to prevent this from happening by adding a plastic sheet or waterproof membrane behind a wood-mounted system․
The good news to the vertical gardener in Tennessee is finding plants appropriate to our humidity and heat within the structure is better than the generic "shade-tolerant" or "drought-tolerant" suggestion that in fact does not understand that we tend to have both a wet summer and a cold winter․ Using natives and other tried-and-true plants that like the Southeast best‚ with good drainage and good airflow‚ the problems we'll have will probably be minimized․
