1969

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Chapter 2 - Climate and Soil

The combination of a fertile soil, a temperate climate and the varying contours of the ground makes it possible to grow a very wide range of plants and trees in the gardens on the University Estate.

The dominant influence on the climate is the prevailing air stream which comes across the Atlantic. In the Exeter District these westerlies are tempered by the high ground to the west and gales occur on not more than a dozen days in the year. Dartmoor also creates a rain shadow around the Exe estuary and the mean annual rainfall is only a little over 30 inches the year. The driest month is normally June with an average of less than two inches of rain. Autumn and winter are relatively wet while the early months of spring are usually fairly dry. The number of days on which more than 0.4 inch of rain is registered is surprisingly low, but some measurable rain, that is 0.01 inch or more, falls on about 180 days in the year. Snow falls, on the average, on less than 10 days a year and only on half of these occasions is it cold enough for the snow to lie.

Many plants, even from sub-tropical regions, will tolerate short periods of frost. The first screen frost in Exeter does not usually occur until early November and growth may begin well before April. The average of the lowest temperatures recorded an Exeter airport over the past 27 years is minus 7.7 degrees centigrade. The air temperature falls below freezing point on only about 25 days in the year and fails to rise above 0 degrees centigrade on only one or two days.

The mean average monthly temperature reaches its maximum of just over 16 degrees centigrade in June falling to 5.5 degrees centigrade in February, usually the coldest month of the year. This in itself is unusual since January is generally accepted as the coldest month of the year in Great Britain. Many plants cease to grow when the temperature falls below 4.5 degrees centigrade so clearly plant growth can take place most of the year, though occasional sharp frosts in the early autumn or late spring can be very damaging to young growth. Warm sunny walls where they occur in the gardens provide protected sites and most plants which tolerate a moderate frost can grow and thrive.

Sunshine, of course, has a marked though less direct effect on plant growth. The daily average ranges from just under two hours in December to over seven in June. In all, Exeter enjoys about 1,600 hours of sunshine per year. Air pollution reaches only low levels in this area, and consequently conifers and other evergreens are not damaged and grow remarkably well. The main climatic hazard is the dessicating east wind which occasionally blows for several weeks in the late winter and early spring.

The university property forms very roughly a semi-circle convex to the south and west. The highest part - the playing fields at the top of the central estate - is about 350 ft above sea level and lowest - the grounds of Thomas Hall - about 60 feet. In general, therefore, the slope of the ground affords a measure of protection from frost.

The soil varies in depth, being rather a thin cover on the slopes above Reed Hall but much deeper in the lower areas. The underlying rocks are Culm Measures of Carboniferous age, locally called "shillet". In the eastern part of the Estate the soils may be considerably influenced by downwash from neighbouring New Red rocks. In either case the soil is a rather heavy clay loam which is not infertile but in which it is sometimes difficult to establish young plants. It is markedly deficient in potassium and to some extent in phosphate and organic matter. The pH value lies generally on the acid side of neutral.