In many landscapes, plant selection and placement raises some debate especially when working with indigenous plantings.
There are various philosophies and approaches, but at the end of the day, what is wanted and needed is a selection of plants that will thrive , grow and fit aesthetic and environmental requirements.
Tried and true
When nature tries a plant – it tries it to the limit. When dealing with difficult sites, indigenous plants are often an excellent solution especially if a benchmark site can be found where local vegetation can be studied, or where the conditions are very similar. Karoo plants, for example, can generally be classed as drought tolerant as well as heat and cold resistant. Nevertheless, a study of a relatively natural site as close as possible to the area to be planted will give inspiration, confidence and valuable first-hand experience.
In nature, plants find ecological niches for themselves, but this is not necessarily an indication of the only conditions under which they will thrive. Given that competition and other limiting factors tend to be eliminated or minimised in the cultivated landscape, plants can be established over a greater range of environments.
The way a plant looks is not really an indication of its toughness or adaptability. Many delicate-looking plants, like Freesia alba will perform well in harsh conditions. The dainty Falkia repens with its soft pink flowers and wonder-lawn like leaves is another example tolerating heat, drought, poor soil, just about anything that nature throws at it despite its soft appearance.
Even where irrigation is in place, drought tolerance in dry climates is a decided plus. Without irrigation, especially during the establishment of plantings, extreme drought resistance and planting during the rainy season are essential. Water holding gels added to soil at planting have been of enormous help in the success of many such projects.
Plant choice questions to consider in this case include container size – plants from larger containers have deeper root balls and will not dry out as much – as well as the requirement for drought tolerance.
Just about all plants need some moisture!
Some plants that have a reputation for being finicky, are as tough as nails once the crucial establishment phase (with extra attention to mulching and irrigation) is past. Erica cerinthoides and E.gracilis are examples. Many Restios are also enormously drought tolerant, but only once the roots have been able to spread into the natural soil, once again, extra watering is only needed in the first seasons.
See also: Sloped gardens and how to plant them up
Most of our Indigenous plants tolerate drought fairly well, but poorly drained soils can create ideal conditions for root rot. Cussonia, Dais, Buchus, Ericas and many more species will not grow successfully with ‘wet feet’.
Of course, one solution is to adapt the site, improving drainage, but where this is not viable or practical, plants adapted to bog conditions are the solution. Most will tolerate seasonal or intermittent drought, but at testing time, when the soil is soggy, they will grow strongly and also help to dry up the excess water to a certain extent.
There is quite a broad choice of plants here: Cyperis species, Typha (bullrush) and certain restios not only tolerate but thrive in these circumstances. Finely textured fountains of Juncus effusus grass or bold fans of Wachendorfia thyrsiflora foliage can add interest. Gunnera perpensa or river pumpkin and Berula erecta with its candytuft-like flowers run riot along the ground. These ‘problem areas’ can become oases of greenery.
Brackish damp soils are not as much of a problem as one might expect. A walk along a tidal estuary will reveal a wealth of plants that perform well despite the saltiness of soil and water and variations in water level. Falkia repens together with silver, succulent Chenolea diffusa, are good examples tolerating changes from drought to flood. Trees like Rhus glauca grow well provided the water table is not too high, but Rhus chirindensis, a handsome tree with a spreading crown seems to grow tall and strong even under these conditions.
There are no hard-and-fast-rules regarding light requirements. Plants in the cultivated landscape often perform well despite stronger or weaker light intensity than that found in their usual environmental niche. Most plants that will grow in lightly dappled shade will also grow in sun and most sun loving plants will adapt to light shade. Plants that usually require deep shade will often tolerate a little morning sun, but not the heat of the afternoon sun..
As landscapers know: this is more of a placement limitation than a plant choice limitation. Exploration of local vegetation and knowledge of the origin and habitat of plants from other parts of the country can be invaluable. Although many plants are more adaptable than one might expect, certain plants have undeniable requirements for warm or cool temperatures.
Where winds are strong or salty, specific plants are needed to create more hospitable conditions for people as well as more sensitive plants. Buddleia saligna and Tarchonanthus camphoratus are examples of wind-tolerant trees that create protection.. Scrambling shrubs such as Phylica axillaris, Rhus crenata, and Grewia occidentalis are fast growing pioneers that create shelter for more delicate plants. A harsh site need not result in a limited plant choice provided that the wind is blocked.
Environmentally sensitive areas
In environmentally sensitive areas there may be a requirement or preference for endemic species. A thorough survey of the site and surrounds will yield an extensive plant list, and many of them will be available for purchase in the trade.
The question however, especially in relatively pristine areas, is whether the genotype belongs there.
Some of our plants like Polygala myrtifolia are extremely variable, and the physical appearance may differ considerably from place to place. Even if there is no apparent difference, bringing new genes into an established gene pool may have unpredictable results.
In sensitive areas such as this, it makes sense to propagate plants for the landscape from the material existing on and around the site in order to protect the surroundings from ‘alien’ genotypes. An additional benefit is the competitive edge experienced by environment friendly ventures in today’s environmentally aware and issues conscious market.
A thorough plant census listing the species found and where they grow will be the first step in the process. Far sighted-planning will allow for propagation of the site-specific material, and the uses of the different plants within the design elements of the landscape can be evaluated. In pristine areas care should be taken to propagate and place as many of the species that occur on the site as possible, especially if the design is intended to recreate or blend with the natural surroundings.
This ‘best-practice’ scenario requires intensive planning, and propagation should be initiated at least eighteen months before planting is to commence if the species on site are to be well-represented in the finished landscape.
There is a perception that in using indigenous plants, especially endemic species not previously cultivated, the landscaper must try to closely emulate the exact environmental conditions found in the environmental niche it inhabits. This is not necessarily true as cultivation eliminates possible unfavorable factors that previously existed in the wild landscape, in particular, competition.
In pristine areas, an exceptional level of care in planning is of more importance than the actual placement of the plants.
Only certain species, generally ones that are extremely difficult to propagate, have very specific requirements.