Learn With Us, August 2021

The fall catalog of Adult Programming at Duke Gardens is available here. Beat the August heat and get ready for autumn by registering for a class (or classes!).

You can learn about plants, create garden-inspired art, or even practice yoga in courses listed in Triangle Gardener’s Events Pages – click the link and scroll down for August offerings.

The North Carolina Botanical Garden’s complete course listings are here.

J.C. Raulston Arboretum has a number of online offerings and some in-person events here.

Keep cool and think about fall gardening!

My Catawba Rhododendron Adventures On Roan Mountain

By Wendy Diaz, EMGV

In February, I planned a short weekend trip to see the Catawba rhododendron (Rhododendron catawbiense) blossoms in the High Country section of the Appalachian Mountain Region of North Carolina. I wanted something to look forward to in hopes that the pandemic would allow a little careful domestic travel by the time June rolled around since vaccinations had already begun. I always wanted to see them bloom but we never seemed to have the time in our schedule for their schedule; and make no mistake you have to have great timing to witness peak bloom of this state regionally-rare native species in the High Country. The exact timing of the rhododendrons peak bloom depends on several factors mainly the weather (give or take one week) and especially the elevation. In general, they flower in the High Country between June 5 and 15 at elevations of 3,500 feet and between June 20 and 30 above 5,000 feet elevation.

We couldn’t make the trip during the 74th Rhododendron Festival[1] in Bakersville on June 18 and 19, 2021, so the plan was to go a week early and hope that due to global warming there may be a chance to see some early blooms and buds even though they usually peak mid-June at that elevation. We picked a ‘wet weekend’ in the end. We intended to do the 5-mile hike along the high section of the Appalachian Trail from the Carver’s Gap trailhead at 5,512 feet elevation adjacent to NC Highway 261 to the grassy balds along Roan Mountain at elevations of 6,600 feet[2] on Friday, June 11, 2021. Roan Mountain is actually a 7- mile long ridge situated along the North Carolina–Tennessee state line in the Pisgah National Forest and is most famous for the largest known area of several hundred acres of naturally growing Catawba rhododendrons. This area of grassy balds and high elevation Spruce (Picea rubens)-Fir (Abies fraseri) forests is an unique and a fragile ecosystem which are remnants from the last ice-age of the Pleistocene Era[3] over 10,000 years ago when Mastodons grazed these lands. Winter weather here is similar to Canada’s winter and thus the species are very hardy to cold temperatures. 

When we started out in the damp morning from Spruce Pine I was hopeful but as we passed through Bakersville going north and ascended the mountain, the clouds rolled in and the heavy rain began. Driving through Bakersville we passed the highway historical marker NC20[4] which honors the French pioneering botanist, Andre Michaux stating he visited Roan mountain on two dates: August 16, 1794 and May 6, 1795. Other sources state that In 1796, he found the species along the Catawba River[5] when he named the species. Michaux was sent initially by Louis XVI to North America to study trees and access their quality for naval construction but also studied the flora of Western North Carolina[6]. Nevertheless, based on the United States Forest Service Welcome sign to Roan Mountain Gardens, Andre Michaux discovered the Catawba rhododendron a few years before in 1789 on a previous visit. 

Photo courtesty of North Carolina Department of Cultural Resources NC Highway Historical Marker Program (iv)

We arrived at Carver’s Gap in the pouring rain and there was only one other car in the small parking lot so we decided to change plans and drive up to the overlook at the Roan Mountain Gardens at 6,286 feet that only required a short pavement walk from the parking area. It was a good plan because as we got to the summit the rain was too heavy to bring out my camera and as one lone fellow traveller returning from the observation deck answered us when we asked if there were any blooms he quipped “NOT even a bulb!” We smiled and knew he meant ‘bud’.  We dashed out to read the welcome sign and shelter and walked briefly through the Spruce-Fir forest but we were too early. The visibility was poor at the overlook, as we couldn’t see the mountains and the rhododendrons had no blossoms. We did learn that for about 20 years a nearby three-story Cloudland Hotel (dismantled in 1910) welcomed guests to the cool mountain air in the summer and if you dined on the Tennessee side of the dining room you could drink alcohol but not if you sat at a table on the North Carolina side of the dining room. Our weekend plans changed and we had a delightful time exploring the very interesting area’s more sheltered attractions such as an old quartz mine, Penland School of Crafts and geology museums.

US Forest Service Welcome Sign at Roan Mountain Gardens taken June 11, 2021 by Wendy Diaz
Inside historic Bon Ami (Feldspar, emeralds and mica) mine at Emerald Village in Little Switzerland, NC. Photo taken on June 11, 2021 by Wendy Diaz.

As an avid gardener, I was not content knowing that our first expedition was just too early to see the blooms and not too late. So, I convinced my husband that he needed a short trout-fishing trip and a side trip to the Roan Mountain Gardens to check out the Catawba rhododendrons wouldn’t take long on June 25, 2021. My timing was better this trip and it did not disappoint. I took a few photographs before an afternoon storm rolled in. Not enough time for a hike but at least I had a chance to see these beautiful crimson blossoms in their native habitat.

Roan Mountain Gardens Trail Sign at elevation 6,280 ft elevation asl. Photo taken June 25, 2021. Photo by Wendy Diaz
View from observation deck of the Roan Mountain Gardens (facing south) and a short walk from the parking area. Photo taken on June 25, 2021 by Wendy Diaz

Top: Looking west at the entrance to the observation deck. Bottom: Catawba rhododendron shrub in full bloom along the base loop trail of the Roan Mountain Gardens. Note the umbrella-like sympodial growth Photos taken June 25, 2021 by Wendy Diaz

The Catawba rhododendron (Rhododendron catawbiense) is a broadleaf evergreen with a rounded habit that grows 6 to 10 feet tall and 8 to 10 feet wide and forms dense thickets. It has sympodial growth where the terminal bud forms several branches, which resembles the ribs of an umbrella[7]. The 5-inch long oblong leathery dark green leaves cluster at the end of the branches and curl under extreme conditions like when temperatures are very cold. The juvenile stems are yellow. The pink to light purple/lavender flower terminal clusters (racemes) contain 15 to 20 funnel or bell-shaped, five-lobed flowers. Each flower has 10 stamens and the nectar attracts hummingbirds, butterflies and bees and supports the specialized bee: Andrena (Andreana) cornelli. They can grow in the Piedmont but prefer partial shade; organically rich, acidic soil pH conditions and good drainage. The genus name is derived from the Greek words rhodo which means rose and dendron means tree.

It took two trips to the High Country this year in my pursuit of these beauties and both trips were enjoyable (even my husband discovered his talent for micro-fishing) but still on my bucket list is the original hike that is probably one of the most scenic sections of the Appalachian Trail during the third or fourth week of June. Maybe we will have the time and ideal weather next year!

Sunset from foot bridge Spruce Pine on June 10, 2021

Plan your own adventure:

https://www.youtube.com/watch?v=_V4RYh8H_7o https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5366102.pdf





[1] http://www.roanmountain.com/rhododendron-festival/

[2] https://www.fs.usda.gov/recarea/cherokee/recarea/?recid=80287 and http://carversgap.org/explore/#hikes

[3] https://auth1.dpr.ncparks.gov/habitat/view.php?combined_code=1102.0

[4] http://ncmarkers.com/Markers.aspx?MarkerId=N-20

[5] https://scholar.lib.vt.edu/ejournals/JARS/v51n1/v51n1-salley.html

[6] https://www.ncpedia.org/biography/michaux-andre

[7] https://plants.ces.ncsu.edu/plants/rhododendron-catawbiense/

Drats, Gnats! Advice for Container Gardeners

by Andrea Laine, EMGV

In May I received a quick reminder of the downsides of overwatering. Temperatures soaring to 15 degrees above the seasonal average in my western North Carolina neighborhood caused me to give my container garden a second watering in less than a week since the last watering. Now, that might be called for in the middle of a hot summer given that plants growing in containers do not have access to a reservoir of groundwater. But it was still, technically, spring and, more importantly, my plants showed no signs of suffering. I watered in the morning as recommended and by afternoon I had mushrooms popping up in the plastic containers. I plucked them out; Two days later, there were even more! 

Photo by A. Laine, May 26, 2021.

On closer inspection I noticed something else – a number of teensy flies flitting all around the soil surface and sides of the containers. By overwatering, I created a perfect setting for fungus gnats.

Fungus gnats thrive in very moist, warm conditions and feed on fungi. Mushrooms are fungi. So weeding out the mushrooms was a good move; But not good enough. These gnats like to stay put. They live and rapidly breed in the top inch of soil and feed on organic matter and sometimes roots, too. A generation of fungus gnats (from female to female) can be produced in about 17 days depending upon temperature.1 In the right conditions, three to four generations can be produced in a year. As many as 272 eggs have been counted in a single female fly 2.

Fungus gnat on rim of plastic pot. Photo by A. Laine, May 26, 2021.

Another way I may have unwittingly invited the gnats to my garden is by neglecting two pots that contained perennials that did not successfully overwinter. The rotting roots of those plants could have been gnat food. I should have emptied those pots out weeks earlier. (I was hopeful that the plants might miraculously recover.)  

Fungus gnats are most often associated with houseplants where air circulation may not be ideal. My container garden was on a covered deck, so it mimics some of those conditions.

In the long run, the fix for the problem I had created was relatively easy: 1) I continued plucking mushrooms from the containers as they appeared. 2) I applied a neem oil drench to the soil every seven days for one month. Neem oil is a naturally occurring pesticide found in seeds from the neem tree3.  3) When temperatures returned to normal, I moved all the plants off the covered deck and into the yard where they would receive bright sunshine for most of the day and better air circulation. 4) I restrained myself from overwatering! 

Less is more: Water amply yet less frequently. Be sure your containers have holes in the bottom where excess water can drain. Be especially careful about watering plants potted in plastic containers. Plastic is not porous and will retain moisture. It will take longer for plants in plastic pots to dry out.   

Several plants were effected by my error, most were herbs and all have recovered. Only the borage (Borago officinalis) got noticeably worse before it got better. Its form is a little wacky now, but as of this writing (July 7) it is blooming beautifully and is visited by many bees.

Footnotes and Additional Resources

  1. http://ipm.ucanr.edu/PMG/PESTNOTES/pn7448.html
  2. http://pss.uvm.edu/ppp/pubs/el50.htm
  3. http://npic.orst.edu/factsheets/neemgen.html


Gnats on houseplants:

July: To Do in the Garden

By Gary Crispell, EMGV

It is July!  It is not hot.  You only think it is hot.  Hot is 114-in-Portland, Oregon-with-no-AC.   That, my friends, is HOT.

 June turned out quite well, I thought.  It would have been nice if Raleigh had shared a little more of their over abundant rain, but then, when has Raleigh ever shared anything good with Durham?  The gardens in our yard look pretty good right now except for the tomatoes that the voles got to… again.

They were not intimidated by the overlapping double layer of chicken wire in the bottom of the raised bed.  Next step is hardware cloth.  I’ll let you know about that next year.

The Accidental Cottage Garden is showing off presently.  There are black-eyed Susans (Rudbeckia fulgida), prairie cone flowers (R. hirta), coreopsis (Coreopsis lanceolata), liatris (Liatris spicata), Stokes aster (Stokesia leavis), balloon flower (Platycodon grandifloris), purple cone flower (Echinacea purpurea), Asiatic lily (Lilium x ‘Corsica’), gallardia (Gallardia pulchella) and a Hydrangea x ‘Limelight’.  The most amazing thing right now is the saucer magnolia (Magnolia soulangeana) that is reblooming.  Can’t say that I have ever seen that before.  Enough about our gardens.  Let’s put on some sunscreen and insect repellent and go out into yours.


Fertilize warm season grasses (Bermuda, St. Augustine or zoysia) now if you haven’t already done so.

Mow these grasses by removing no more than 1/3 of the growth.  Mow cool season grasses (fescue, bluegrass and perennial rye) at a height between 3” and 4”, no lower.


Last chance to fertilize landscape plants until 2022.

It is an excellent time to take soil samples and send them in to NCDA for FREE SOIL TESTS.  Boxes and instructions are available at the Extension office, 721 Foster St.  They are only free until November.


It is not too late to plant pumpkins, broccoli, beans, collards, Brussels sprouts, carrots and even tomatoes.

Get a jump on the Fall garden by planting seeds of cruciferous plants (cabbage, cauliflower, brussels sprouts) to be transplanted in mid-August.

Pot up or transplant overgrown house plants.


Trees that bleed a lot when cut (E.g. birch, maple, dogwood, elm) can be pruned this month.

Knock down those overgrown landscape plants and hedges.  August is too late.

Coniferous plants (seeds are produced in cones) can be lightly pruned now.

Keep garden mums pinched until the middle of the month for Fall blooms.

Blackberry and raspberry fruiting canes can be cut back to the ground after the last blackberry cobbler of the season.

To get a rebloom on perennials prune them lightly after the first bloom and before they set seeds.


Be on the lookout for these nefarious characters, bag worms (pick off the bags), leaf miners (take away their little headlamps), spider mites, aphid, lace bugs, and Japanese beetles. Spray sparingly and follow the instructions on the label. For many things, nothing more than insecticidal soap is needed.

Be aware of tomato blight and treat as necessary.

Continue the perpetual program for roses, fruit trees, and bunch grapes.

Pests of vegetables that are active this month include cucumber beetles (on cucumbers, ironically), flea beetles on tomatoes, beans and eggplants and aphids on anything they can get their sucky little mouth parts into.


If you are just bored you can build cold frames or greenhouses in preparation for the winter to come (‘cause it will come).  Personally, I am going to go out and sit under the gardenia (Gardenia jasminoides) in the backyard with a cold beverage and luxuriate in the heavenly odoriferousness of the blooms while listening to the indigenous wildlife communicate with each other.

So, let’s all get vaccinated so we can gather in the garden with friends.  Enjoy July, y’all.

*Resources and Further Reading

All About Soil Sampling and How to Get Supplies from Durham County Cooperative Extension

Organic Lawn Care Guide

Central North Carolina Planting Calendar for Annual Fruits, Vegetables, and Herbs

General Pruning Tips

Learn more about insects and how to control them from the North Carolina Extension Gardener Handbook

NC Extension Gardener Plant Toolbox (find your perfect plant or figure out what that unknown weed is!)

2021 Tomato Project

Last year’s tomato project, in which we compared the yields of grafted heirloom Pink Berkley Tie-Dyes to ungrafted Pink Berkeley Tie-Dyes, got us wondering if we could find hybrids that pleased our palates just as much as our favorite heirlooms.  Our curiosity was further piqued by the research going on at Klee Lab at the University of Florida, and the opportunity to participate in his trials as “citizen scientists.”

Since 1995, Dr. Klee has been trying to create the “perfect” tomato, one that: won’t bruise during shipping, resists many of the major diseases, is highly productive, and actually tastes good. According to Dr. Klee, “when we bite into a tomato, what our brains register as a “tomato” is actually a complex interaction between sugars, acids, and multiple volatile compounds.” He has reduced the essence of tomato to only 15 – 20 compounds that impact our perception of the fruit.

His first tomato, Garden Gem, was a cross between Maglia Rosa, rated by consumers as the best tasting tomato, and a “tasteless” workhorse, Fla. 8059. In variety trials among “a large consumer test panel run by the University of Florida Food Science and Human Nutrition department,” only two points separated Garden Gem from Maglia Rosa. In eighth place, Better Boy, the tomato most planted by home gardeners, ranked more than 12 points below Maglia Rosa.

The immediately identifiable shape of a Garden Gem.

As part of Dr. Klee’s citizen science project, we will compare performance, yields and taste among three of his hybrids: “R” Hybrid, “B” Hybrid, and an improved “Garden Gem”and against the hybrid classic, Better Boy. Expanding the project for ourselves we will also compare these four tomatoes with a variety of heirlooms which ranked high in our own taste tests, along with some new varieties we have learned about including three new offerings from Craig LeHoullier. We’re excited to see how the hybrids and heirlooms compare in terms of both performance and flavor.

Here’s what we’re growing:

Better Boy, Determinate Hybrid

Black Cherry, Indeterminate Heirloom

Black Krim, Intermediate Heirloom

Blazey F2, Craig Le Houlllier  (Honor Bright x Blazing Beauty)

Chef’s Choice Black, Indeterminate Beefsteak Hybrid

Cherokee Purple, Indeterminate Heirloom

Lemon Boy, Indeterminate Hybrid

Pamela’s Sundrop,  Craig Le Houllier (small yellow)

Pink Berkeley Tie Dye, Indeterminate Heirloom

R Hybrid, Klee Lab U of Florida,  Hybrid

Shin Chang Gong, Rootstock

Sun Sugar, Indeterminate Hybrid

Suzy F2, Craig Le Houllier (Sweet Sue x Peach Blow Sutton)

Once again, we’ll spend Tuesday, Thursday, and Sunday mornings at Briggs, grooming, picking, counting, and weighing our way to tomato Nirvana.  Except for those tomatoes in our end-of-season taste test, the produce will be donated.

Stay tuned for updates.