Submitted by blazej on
Mariel Tribby

HORTICULTURALLY, 2013 WAS a big year for me. I had just graduated from Longwood Garden’s Professional Gardener Training Program and completed internships at the Royal Botanic Garden Edinburgh in Scotland and Lautaret Alpine Botanical Garden in France. It was on the second interview at Missouri Botanical Garden that I caught my first glimpse of the newly-renovated Bavarian Garden. It had been transformed into a rock garden, and I remember thinking, “I would love to have this garden” as I took in the sandstone boulders and beds waiting to be filled with plants. During the interview, I had mentioned my interest in alpine plants and here was a new garden dedicated to alpines! At the same time, I knew I was applying for a different area of the garden, so was only hoping that I would be able to help out from time to time. I moved to St. Louis two months later to start my new position, blissfully unaware of the challenging climate that awaited this novice rock gardener.

The renovation of the Floyd Pfautch Bavarian Garden began in late 2012 and had just finished as I arrived at Missouri. I became involved with plant selection and planting in late spring of 2014. That first year, we ordered plants from Arrowhead Alpines and Wrightman Alpines. We also planted a generous donation of plants from Mike Kintgen and Denver Botanic Gardens. Since then, we have grown plants almost exclusively from wild-collected seed sourced from Indices Semina and seed exchanges. Here I have to mention our talented wild-species propagator Justin Lee, who produces countless quality plants for this garden each year.
The garden serves as an extreme trial for these plants. Can they quickly adapt to a harsh climate that is almost the opposite of their native environment? These conditions may become a reality for alpine plants due to climate change. Another function of the garden is to add diversity to our collections, particularly plants of conservation concern. Alpines face several threats including climate change, human development, and overgrazing. Due to the high number of threatened species, including endemics, many alpine areas are considered biodiversity hotspots in need of conservation. By pushing the boundaries and displaying these plants to our visitors we can raise awareness of the threats and increase appreciation of this flora.
Structure of the Garden
The beds are laid out in a series of terraces and slopes bounded by sandstone boulders. The soil in these original beds is a mix of topsoil and Turface (a fired clay soil amendment), which has proven too heavy and moisture-retentive. The flat areas on the terraces also have problematic drainage, so the slopes have become very valuable space. I use expanded shale extensively around the crowns of plants and incorporate it into the soil at planting time in these beds, but this does little to help with drainage. Luckily, there has been room to build up new beds within the garden. When I inherited the garden in 2014, several areas had been left rather flat and devoid of rock. Over the years, I have raised these areas and used different soil mixtures to help increase drainage. My first mixes combined equal parts topsoil, coarse sand, and expanded shale, which resulted in some increased plant survival. Most recently, I have added a bed using a base layer with 50% topsoil and 50% expanded shale. The base layer was about 1.5 feet (45 cm) deep. On top of that is a layer of 50% coarse sand and 50% expanded shale. The top layer varies from 1-2 feet (30-60 cm) deep. This two-layer system, which keeps the crowns of the plants dry, but encourages the roots to grow deep for moisture from the base layer, is the most successful growing format so far.
The garden came to me accessorized with large cast stone concrete troughs. I quickly discovered the fun of creating a small landscape within a trough, which showcases the more diminutive plants that get lost in the large terrace beds. I also tried several mixes within these troughs, blending equal parts compost or topsoil with sand and expanded shale. Like the beds, these troughs hold more moisture than is favorable, but I have also had more success with keeping plants for longer periods of time in troughs. Last year, I used some of the 50% coarse sand, 50% expanded shale mix to fill two troughs. Sand is a very unforgiving medium to plant into, but with careful attention to water, many plants can thrive without organic material.
I also added a few pieces of tufa to this garden from the 2015 NARGS Annual General Meeting in Ann Arbor. These were sited in a bed that receives afternoon shade. In my first experiment with planting directly into the tufa, I used small plants of Saxifraga paniculata and S. cotyledon. These lasted almost a year but expired in the summer. I have also tried Draba bertiscea with similar results. I am eager to try direct planting again with slightly different methods of drilling and backfilling and to attempt direct sowing onto the tufa.
The garden is outfitted with a sprinkler irrigation system, which I use very rarely. Usually, when it’s been a few weeks with no rain, I’ll run the irrigation and later that day we’ll receive an unexpected heavy downpour. Most of my watering is done by hand, sparingly, to establish new plants. Three emitters are sited throughout the garden with the idea that mist nozzles could be added to the irrigation system in the future. Misting seems to be a recipe for disaster, but I did use one of the emitters to create a seep feature in the garden, where water drips out of small tubing snaked in between rocks. I built up around these rocks with the aforementioned sand/expanded shale mixture. So far, I have only planted Aster diplostephioides in the flow of the seep, but it has been doing well in its first season.
The Plants
Tucked on the far south end of the Botanical Garden, the Bavarian Garden does not receive a large number of visitors. This is understandable for most of the year, but from April to June the garden is at peak bloom and a delight for an observant visitor. It is a time when I feel very grateful for the chance to grow these plants despite the setbacks that may be looming in the summer.
Outside of spring and fall, there is not much going for these plants. The hot, humid summers take a toll, as well as the torrential rainstorms which are most common in the spring and summer. The garden is in full sun for most of the day, and I’m sure it’s one of the hottest places in St. Louis during the summer. Winters, as far as I have experienced, are very variable with occasional subzero (below -18ºC) temperatures. There is little persistent snowfall to insulate plants. The soil does not stay frozen which, paired with winter rainfall, can lead to rot.
Due to this climate, I have learned not to take any plant for granted. Those that have survived, even thrived, for a few years can suddenly die off at any time. I continue to try new plants, and the garden fills in a little more each year. I do keep some alpine look-alikes from lower elevations in the garden for their reliability. However it is not all bad news, I have found a number of plants that stand out as tough and dependable. Some alpines do seem to be able to adapt to this climate!
Antennaria carpatica was one of the first plants put into the garden. The four original plants have grown together to form a large mat of silvery foliage. The mat is thick enough to keep out weeds almost entirely. It continues to creep across the coarse gravel mulch each year and puts up small clusters of rosy-pink flowers in early spring. It is easy to divide, and clumps that I transplanted last fall have established well. The first planting is near the top of the garden, but the transplants are lower down near the path, so it seems to be very adaptable to different levels of soil moisture.
Another tough mat-former is Teucrium montanum. Though not a true alpine, it must be included because it has done so well in difficult locations in the garden, including hot slopes and flat areas with more moisture. It becomes covered with white flowers in May, with some sparse bloom throughout the summer.
Hypericum kazdaghense has thrived in a fairly flat location along the path. The original five plants have spread into a rectangle roughly 4 feet (4.2 m) wide by 8 feet (2.4 m) long over the past four years! It is not a continuous mat, and there is some dieback and regrowth each year. The yellow flowers in May are held right on top of the foliage.
Petrophytum caespitosum has slowly filled in between rocks with its tight mat of light green foliage. It blooms in late summer, sending up stalks of white flowers. It has a wide range over the western U.S., which I believe leads to the adaptability and durability of this plant.
Globularia cordifolia is another nearly impenetrable mat-former that seems very adaptable. It also transplants well, with divisions from last fall growing on a hot slope. I have both cultivated and wild-sourced plantings in the garden, some in full sun and some in more shade, but haven’t seen any of the purple blooms yet.
Asperula nitida subsp. hirtella grows well in a trough, blanketing the surface and hanging down off the back edge. Its tiny pink flowers cover the foliage in late spring, with some rebloom in the summer. Troughs have also been good homes for Alyssum ovirense and Alyssum propinquum. Both have attractive silver foliage and reliable yellow blooms in early spring.
Many iris have taken the conditions of the garden in stride. Currently, there are 15 taxa in the garden, with Iris pumila standing out from the rest. I love its dark purple flowers in April. The plants are very vigorous, and I have been able to divide and establish a second planting. Blooming at around the same time are several species of Pulsatilla. P. dahurica is my most recent addition, producing small purple bell-shaped flowers. A second plant seeded in, artfully tucking itself in front of a rock.  
Lastly, I’ll mention Sibbaldiopsis tridentata. I recently saw it growing in wind-whipped crevices near the coast at the Newfoundland Annual General Meeting. In Missouri, the plants growing in full sun have limped along, but a recent planting in part shade is doing very well and producing runners. I saw a few flowers this year for the first time.

From my experiences, I would like to offer some humble advice to beginning rock gardeners who live in similar climates. Troughs are a great way to start. It allows you to create a small garden with well-drained soil and to be able to site it in the best conditions. You can try a few plants without too much commitment. When you are ready to move into a space in your yard, choose an area that gets afternoon shade if possible. Build up the soil using a well-draining mix and resist the urge to water once your plants have established. Look into local natives that are low-growing and which will be well-adapted to your area. These can be the reliable plants that form the backbone of your garden. In the Bavarian Garden, Clematis fremontii, a glade plant from Missouri, Kansas, and Nebraska, fits in well with surrounding plantings and has no issues with our conditions. Geum triflorum, which is native across the western and northern U.S. has also worked well in the garden. For more experienced gardeners, don’t give up! Try new species from different regions of the world. The NARGS seed exchange is a great place to find this diversity. I hope this article has provided some inspiration for your own garden!