Interplanting with Gentians
The biggest pleasure of the past season was watching the new plantings of Chinese gentians growing in the garden. Gentians are slow to develop. G. acaulis takes 3 or 4 years to form a mat/mound of ~15 cm circumference. At that size, it is a colony of individual plants both competing and helping each other to survive. As the mound expands, the population increases. It adds to the vigour of each individual. Observation: gentians like company.
One can also plant a single gentian within a low growing mat and see a similar enhancement of growth. We use Arenaria spp., Gypsophila aretioides, Raoulia tenuicaulis, Androsace villosa types, etc. for this purpose. Basically, the mat should be non-invasive and with shallow roots. Gentians will have longer, thicker roots. Some will push deep into the soil. The sympodial types such as G. verna will also make numerous shallow roots from the branches as they sprawl out along the surface. Monopodial types like G. septemfida will send out roots from the crown only. Both types will benefit by having the crown within the mat, which will mediate the scorching sun of summer and the cold wind of winter. Perhaps the whole host of micro-organisms that are associated with the mat are more beneficial also.
Traditional gardening has agricultural roots; i.e., the planting of a single species for some useful, human purpose. Nature, however, is complex and decidedly messy-lot's of different plants growing together in a mix of rivalry and alliance. So, when plants are found to be "difficult", the requirements are not being met. As a grower I know that it is much easier to grow any plant in situ than in a pot. Small pots are for short term_2 years max. Much of the problem is degradation of organic soil mixes. The garden, on the other hand, including our troughs, is our experimental site where we try to create the best conditions we can. Here we can use real soil and have the advantage of mass as well. For help in fine-tuning garden conditions, it helps to read the seed collectors field observations. Plants described as growing in "high alpine tundra" implies a plant community growing in seasonally wet conditions in soils that are reasonably fertile. "Rocky pastures" indicates a drier site; the boulders are more ornament. Plants growing in "fissures on cliff faces" are a wonder. The narrow spaces they inhabit must be filled with soil particles that arrive on the wind-smaller sized silt and clay particles that will stick together. These fine-textured soils absorb and retain water.
Back to our gentians. In a trough garden, G. szechenyi sits nestled in a clay crevice that is well elevated. So two criteria are met: the crown remains dry, and the water and nutrition are there-just deeper down in the soil. Like many of its cousins, it is a thirsty, hungry plant with an additional need for a dry crown. Sometimes in the heat G. szechenyi will wilt; but a splash of water soon revives it. It's hard to imagine how it can manage to flower in such an opulent, luscious fashion. In nature the crown will sit elevated, while underneath may be a wet, boggy meadow.
Another way to protect the crown is to plant into a mat or low mound on flatter terrain where the availability of moisture in the soil remains high. Mojmir Pavelka has an amazing photo of G. szechenyi growing on a large, old hummock of Androsace tapete - imagine that! Once again the crown is sitting high and dry, but the roots can range down to the wetter tundra below. In the garden, one can create such hummocks with appropriate mat or mound forming plants. The choice then becomes what special gem is planted in the hummock. Planting into an established mat minimizes disturbance to the look of the garden. Adding these 2 techniques - clay/crevice planting and mound/mat interplanting, is most useful for trough/container planting or a garden space that is small in size, but otherwise ideal. The methods are really quite simple. It takes only a slight change in approach.