Cultural Groundwork for an Alpine Garden
Good understanding and management of garden culture can spell the difference between a mediocre garden and a superb one. There are five basic elements to consider which control the growth and health of plants in the garden. Some elements can be regulated more easily than others. They are climate, soil, light, water and nutrition.
Obviously, climate is the one you can't affect, unless you move. The same complaints are heard everywhere about the unfavourable climate. The truth is, you must live with it and control the other elements effectively. This is an intellectual proposition, not a Zen moment.
There is a plethora of different soil mixes recommended for an alpine garden and it is truly daunting for a beginner to decide what to use. Perhaps the best advice is to go native, and use what is commonly available in your area. It can only help to note what other gardeners are using locally. Still, the problem of what to do with uncommon, special situation plants will arise. There are general guidelines to follow, but each location and climate zone will have its own variations. Fundamentally, the higher the amount of rainfall received, the more porosity the soil should have resulting in a lower amount of incorporated organic material and consequently lower disease pressure from various fungi and bacteria that grow in moist environments.
For example, Southern Ontario receives ~100mm of precipitation through the year and humidity levels range from 40%-90%. Accordingly, we have built our crevice gardens using sand with no organic content. A top dressing of grit or gravel is applied between the stones to provide a drier condition around the stem of the plant helping to prevent crown rot.
By contrast, Calgary receives about half as much precipitation with much lower humidity levels. As a result, rock gardeners there can use much heavier soils - even the native clay-loam, which has a high nutritional level.
A new development in soils is the use of tufa, a natural stone with a high aeration factor. Tiny root hairs are able to penetrate tufa and derive nutrition from the stone; something that can't be done with impervious limestone or granite. Because of its chemical composition, which includes compounds of calcium, magnesium and to a lesser extent potassium, it has an apparent buffering capacity which helps in the absorption of nutrients. Tufa can be regarded as being a well-aerated clay, which doesn't compact and lose its porosity. As a top mulch, tufa gravel has the valuable characteristic of acting as insulation to help maintain cooler soil temperature in summer heat.
Plants growing in containers are subject to even greater variation of soil temperature and moisture level. Porosity of the mix helps to moderate these fluctuations. Regardless of climate zone, a basic mix would include 60% coarse sand and 40% peat or composted pine bark. Addition of pumice or tufa grit is helpful.
The further South and hotter the location, the greater the requirement for some shade, especially at mid-day. It is always safe to say that morning sun (eastern or northern exposure) is the best for sun and drought sensitive plants such as primula and saxifraga; but don't make the mistake of giving too much shade, as light is necessary for healthy growth and flower production. This will require some observation of what others do locally and some judicious experimentation. Alpine plants prefer bright conditions with good air circulation, encouraging compact growth and lessening disease impact.
All of the really good growers know that control of water is the most important of the five cultural elements; and again, how it is applied depends on where you live. In the temperature mid-west and east, where humidity is high, it is better to water in early morning when it is coolest. This best combats the drying of the leaves that results from the increasing heat throughout the day. Applying cold water in the heat of the day would add undue stress to the plants and should be avoided. The amount of water should be sufficient to wet the soil, but not saturate it. Automatic sprinklers, wonderful as they are, need attending to ensure the correct amount of water is being applied. In the garden, I prefer watering with a hose and wand.
Quality of the water (its dissolved salts content) is important too. Without a "mineral" test this cannot be known; and, even if you have to send a sample in to a lab, it will be the best $40 you ever spent. Water collected from rooftops will be very pure and have a pH in the neighbourhood of 6 after sitting for a few days. It is ideal for irrigating. Ground water, particularly deep well water, varies widely in its mineral content, in response to the soil and rock strata it is exposed to. A greenhouse mineral test will tell you what the stew is, and suggest corrective action if necessary. The mineral salts present may be benign or may interfere with growth of plants. To know, you must test.
This component is deeply entwined with the soils and water. In general, the richer the base soil is, the less need there is for fertilizing. Where needed, nutrients may be added in granular form or dissolved in water, or both. Typical dry granular fertilizers (e.g. 10-10-10) are useful when applied in early spring, much as grain farmers do with wheat. Earlier application is better, as spring rain will dissolve and release the nutrient salts. The main advantages are ease of application, and less need to reapply. Liquid formulations need to be diluted to the correct level; and because the absorption is more direct, should be dissolved in relatively clean water - i.e. naturally low in dissolved salts. The reason being that the salts within the irrigation water will compete with the nutrient salts in the fertilizer. Therefore, rainwater is best. With that provided, nutrients are better absorbed at a lower level of application.
The number of fertilizer formulations offered to the consumer is bewildering. Some of the factors that affect nutrient uptake are:
Water Quality: again de-ionized (rainwater) is best.
pH of the Fertilizer Solution: I have found in practice that this varies a lot with the different formulations. Ideally the solution should have a pH ~6.5. Above pH 7 or below pH 6, the absorption is less efficient.
Accumulation of salts: Industry studies have detailed the deleterious effects of excess salts. Even elements that are nutrients can be over-applied and produce stress in plants. It can be compounded by the addition of excess mineral salts found naturally in the irrigation water. The implication is that as more irrigation water is applied because of drought, the salts (nutrient and otherwise) accumulate and adversely affect plant growth. In containers, this can be a major problem. One of the great benefits of rain is that it washes salts from the garden. It all goes back to using a clean water source.
As an aside I should mention that Europeans have access to liquid formulation of Wuxal, made by a German company called Aglukon, which has done an extensive amount of research into nutrient matters. I became aware of this through Josef Halda who indicated that they are widely used in the horticultural industry in Europe. The Wuxal line includes a large assortment of different formulation catering to the hort. industry and its various specialties. At present only 2 labels are imported into North America, Wuxal Microplant (high in manganese) and Wuxal Calcium (high in calcium), both are targeted at the orchard industry and are not general purpose type fertilizers. I was able to obtain a trial sample of the Wuxal Super (8-8-6) liquid solution and already it shows some interesting characteristics. The most significant being that solutions are buffered to about 6.3 - 6.5 using either our rainwater or the pond water (which is similar to Lake Huron water in its composition). At the time of writing (mid-Nov.) observations are preliminary but I think this product is an improvement. The big hurdle will be to convince the importers (United Agricultural Products) to bring in a shipment and start selling it. www.aglukon.com
Lastly, native conditions under which the plant grows need to be considered. Some generalizations are possible, but the differences are significant too. For instance, while all primula need a rich soil, some, such as p. auricula, will grow fine in quite hot and dry sites while others, such as p. veris, will need cooler, wetter conditions. For specifics, plant and seed catalogue notes can provide the info, but it's always good to have some reference texts. Some that I have found to be especially good are: Alpine Plants of North America by Graham Nicholls; Bulbs of North America by Mary Jane McGary; The AGS Encyclopedia of Alpines; specific genus monographs, of which there are many - Josef Halda's in particular have good descriptions of habitat.
My experience to date leads me to believe that all the problems you will encounter with alpine plants are conquerable _ so take heart. Growing the more peculiar plants serves only to force just the sort of discovery process that is refreshingly stimulating to the intellect in this overly pre-packaged world.
(2005 Catalogue Introduction)