Hopefully the weather has improved sufficient to allow our thoughts to turn to some outdoor activity but we still need to be wary and I quote from a 1938 Amateur Gardening Every Day Log Book.
If Candlemas Day (February 2nd) be fair and bright Winter will have another flight. If on Candlemas Day it be shower and rain. Winter is gone and will not come again.
All the months in the year curse a fair Februeer. February fill dyke. Be it black or be white
Better if it be white it’s better to like. The second month of the year may witness greatly accelerated activity in various types of plant life. The hours of daylight become appreciably lengthened, and although intensified coldness is a likely accompaniment or heavy rainfall may enforce temporary suspension of outdoor work, the increasing daylight will have a marked effect upon things under glass. Many plants which have slumbered through December and January show signs of reawakening by the middle of this month, and that may be taken as the signal to start re-potting such plants as require it.
Germination of seeds sown in comfortably heated greenhouses will be more rapid and vigorous than last month, and propagation by cuttings of various kinds of bedding plants may be pressed forwards with increasing confidence of success. Root cuttings of various kinds of hardy perennials will callus and make good growth if put in now; they include anchusas, echinops, eryngiums, phloxes, oriental poppies, and statices.
It will be time, also, to start dahlias into growth from which cuttings are to be made, also lupins and delphiniums for the same purpose.
Outdoor seed sowing so early as February is fraught with considerable risk of failure. Even though germination may take place, spells of bad weather are prone to check and stunt growth of young seedlings. It may, nevertheless, be worthwhile trying a few early sowings on warm borders, especially if they can be covered with cloches or protectors of some kind.
Although the notes above were published some seventy years ago they are still entirely relevant as our climate has not really changed that much and never has conformed to any strict predictable pattern and is not likely to do so. We are all familiar with the notes that appear on seed packets advising sowing dates and some of theses also include other instructions such as do not sow before ‘X’ or do not sow after ‘Y’. Sowing dates are not only dictated by temperature but also by day length – both factors influence the growth of plants. Other important factors in the growth and flowering of all plants are the intensity and quality of the light received, available water and the food supply. Temperature often has a greater influence than the length of day during the growing season of the plant. In the British Isles the lower temperatures of winter restrict or prevent the growth of all but the most hardy plants and kill a great proportion of the half hardy and tender types used in summer bedding.
In many plants that flower during a specific period each year a critical temperature very often affects the formation (initiation) and development of their flower buds. These plants are classified as low temperature plants which initiate and/or develop flower buds below a critical temperature and only vegetate above it, or as high temperature plants which initiate and/or develop above a critical temperature and vegetate below it. This critical temperature differs for various species of plants. Low temperature plants include Buddleia, Calceolaria, Cypripeium, Cytisus, Digitalis, Gardenia, Gladiolus, Hyacinths, Bulbous Iris, Narcissus, Rhododendron, Tulip and most perennials.High temperature plants include Chrysanthemum hybrids, Hyacinths, Bulbous Iris, Narcissus, Rhododendron and Tulip. Plants that appear in both lists require high temperature for bud initiation and low temperature for bud development. Daylength has a great influence on a second broad group of flowering plants to the extent that when temperatures are high enough for growth to occur freely the date of flowering may be entirely dependent on daylength, light intensity, or both. A wide range of such plants require certain daylength conditions for flowering and will only vegetate at other times of the year. A long-day plant is one that ceases to flower or flowering decreases with decreasing daylength, and a short-day plant is one that begins to flower or increases flowering when the length of day is sufficiently shortened.
Long-day plants include spring cereals, lettuce, spinach, radish and potato and Short-day plants include tobacco, mid and late season chrysanthemums, salvia,poinsettia and cosmos.
Some plants including tomato, dandelion, buckwheat, and cucumber are ‘day neutral’ in that they flower readily under any length of day provided other factors are favourable. A fourth group consists of a few plants which are classified as ‘intermediate’ in their reaction to daylength and will only flower between twelve and sixteen hours of daylight. The practical result of the above has an effect on plants we all grow. The flowering bud in a tulip bulb will not develop until the bulb is subjected to at least six weeks at a temperature of 46 deg F (8 deg C), fruit set in tomatoes is abundant only when the temperature is between about 55 deg F (13 deg C). As the growth of most plants occurs mainly at night these figures refer to the night period. The flowering period of the popular half hardy bedding plant Nemesia varies widely from year to year and this is because high temperatures early in its normal flowering period of May to June or July will prevent further flower development. The effect on vegetables is much the same we are familiar with the problem of beetroot running to seed if planted too early. This is caused by a cold spell after germination which is why most varieties must not be sown before mid April. With potatoes the changeover from leaf growth to tuber production is governed by daylength not temperature and the overall yield depends on the leaf build up before the days get long enough for tuber formation. The old custom of planting potatoes on Good Friday (which is a moveable feast) is not as silly as it sounds – if Easter is so early that a spring frost kills back the foliage new shoots will be produced because the tuber will already have rooted and will have a reserve of food and dormant eyes. Good Friday rarely falls later than mid April which is significant for the later the seed is planted after 15th April the lower the yield. Much of the research into the effect of temperature and daylength was carried out in the 1950’s by S.A.Searle and L.P.Smith and this has resulted in the development of ‘new’ varieties (particularly of vegetables) that lengthen the availability season of homegrown beetroot, carrots, tomatoes etc. A little understanding of the above will perhaps help us to resist the temptation to sow too early because ‘it feels warm’. An old nurseryman who let me help him during my schooldays used to say ‘watch for weed seedlings – they are mostly native plants and know when it is safe to start growing’.