Adapting Our Gardens

By Sally Arant

In Alaska, we have a variety of environmental conditions, harsh by most gardener’s standards, that affect plant growth and survival. We typically have a six month winter, usually with good snow cover, but not always. Our northern latitude somewhat simulates environments of much higher altitudes. We have a six month growing season with long hours of daylight but not always adequate summer rainfall. Soils are mostly acidic but range from scant inches on top of glacial silt and gravel, to peaty bogs over clay. Native birch, spruce and cottonwood groves are beautiful but root competition with under plantings can be a major problem.

We can’t expect to grow every species of primula in our gardens but we can begin by singling out species or sections of primula to try. With some environmental and cultural adjustments, many primula will adapt quite well to situations quite different than their native locales. Some thrive in quite ordinary garden conditions. Some species may well survive and even thrive here in Alaska better than most other places on earth, with the exception of their natural habitat. Some of our very best garden plants are waiting to be tried!

One should limit the beginnings of a primula collection first to those plants best suited to the limits of the existing garden site. If the site is open peaty bog, choose plants that could adapt to this or a modified version of this environment. If the site is silty and gravely or blessed with interesting topography, look for alpine types or those that love well drained soil. Regular watering can make an enormous difference in these situations. A flat site with poor existing soil is ideal for creating naturalistic mounds or raised beds filled with compost-rich soil. With a partially wooded site, choose those plants that love a cooler situation. A good rule of thumb to remember: species within sections tend to share many physical characteristics and often share geographical origins and habitat preferences.

In general terms, the two main requirements for the survival of most primula species are moisture during the growing season and winter rest for dormancy. They also detest extremes of temperature fluctuation and hot, dry air. Snow acts as an insulator to extreme cold and drying winter winds. In most of the environments where primula thrive, there is winter snow cover and the growing season is also cool and humid, even wet. Temperature, humidity and soil moisture fluctuations are moderate.

Most primula prefer soils that are moist but well-drained (moisture freely moving through the soil and not stagnant), and full of air space for the roots. Some will grow in heavy soils and standing water, but they are a unique group. Most prefer a “dry winter rest” with no standing water near the crowns. Most are also heavy feeders, preferring compost-rich soils. A pH of 5-7 is ideal for most, while a very few prefer slightly alkaline conditions.

We can adjust our garden conditions to approximate those in the wild in a number of ways. For better drainage, we can create new topography by mounding soil and rocks and by adding texture to the soil with gritty material and compost. We can create bog conditions by adding water features and man-made bogs using heavy or peaty soils. Soil pH can be changed with soil amendments. Nutrient-rich soils can be continually replenished with a top-dressing of compost. The afternoon shade cast by high-branched trees, a fence or structure can simulate cooler alpine or woodland conditions. For higher air humidity, a regular routine of watering is often enough.

Plants which detest winter wetness on their crowns or foliage may be covered with cloches, raised panes of glass, or other means of protection.

The problem of root competition from trees can be avoided by carefully selecting bed locations away from roots. Rather than planting around the base of trees, create beds that take advantage of the filtered light they provide but away from the roots. If primroses are placed near trees, liberal yearly applications of leaf compost and regular watering is absolutely essential.

In general, species from marshy or woodland sites prefer soils that are 75% organic compost and 25% gritty material. Soil should be at least 12” deep. Liberally amend soil with leaf compost, animal manure and rough-textured, partially decomposed garden compost, or composted sawdust/shavings. Topdressing around these primula should be with leaf compost.

For bog conditions, most primula prefer moist but free-draining soil. A location in a depression below a pond where the soil can be continually recharged with water is ideal. Bog plants can also often be grown if the soil is deep enough (18” or so) and amended to hold moisture during the growing season but not be saturated in winter wetness. Liberally amend soil with leaf compost and animal manure.

High alpines prefer soils that are 25% (or less) organic compost and at least 75% grit. A base course of 12” of sand and gravel assures good drainage. Above this, a 12” course of silty topsoil or topsoil mixed with leaf compost works well. Topdressing around alpines should be with a few inches of grit. Troughs filled to the rim with this mix, raised beds or rockeries are all appropriate situations for such plants.

Photo Credit: Robert Tonkin of garden auricula grown in the garden of Carmel Tyver in Anchorge