Nature has its own rhythm. This is influenced by the seasons, which in turn depend on numerous factors, mainly the climate and the position of the sun. Each phase is characterized by plants that present a specific growth phenomenon at that time. These indicator plants and phases are arranged together in the phenological calendar, which has been used by humans for centuries.

Phenology: study of phenomena

Phenology is a special field of science that deals with the recording of individual developmental phases of plants. The year can be divided into different phases based on the biological processes such as the flowering period, which are noticeable through indicator plants. The background to the "Doctrine of Appearances" comes from the Swedish naturalist Carl von Linné, who determined the first calendar for the timing of the flowering of various plants. Since that time, the phenological recording of vegetation phenomena has greatly expanded.

As a result, the actual background for exclusive recording has expanded significantly and is now even used by weather services and universities. Farmers, foresters and hobby gardeners also make use of the phenological annual classification, since it is independent of fixed dates. It focuses exclusively on the biological processes.

Notice: The behavior of native animal species is also an aspect of phenology but is not incorporated into the calendar. This is determined exclusively by plants, as these are much easier to observe.

Phenological calendar: explanation

An essential aspect of this science is a "phenological calendar". It is the division of the calendar year into ten sections, which are defined by indicator plants. Theoretically, people have always followed this concept, since wheat, for example, cannot be harvested over the winter. Linné's concept made it possible to record the individual sections even more precisely and use them accordingly. A phenological calendar shows you exactly which phases the year is divided into and which indicator plants appear there. This gives you an overview of the plants that tell you when spring ends or autumn begins. Included in the calendar are:

  • Periods (phenological seasons)
  • pointer plants
  • vegetation phenomenon

A big advantage of this system is the fact that a phenological calendar can be used worldwide. Although you cannot use indicator plants native to Central Europe in Australia, each country has its own species that enable the use of the calendar.

The phases

The phenological calendar follows a model similar to the classic four seasons. Instead of four comprehensive seasons, on the other hand, there are ten phases that are specially aligned with the indicator plants. The phases were defined based on the following growth phenomena that occur seasonally in plants:

  • beginning of flowering
  • end of bloom
  • leaf unfolding
  • leaf discoloration
  • leaf fall
  • needle case
  • needle discoloration
  • Formation of fruit buds
  • fruit ripening
  • harvesting the fruits

Based on these phenomena, the phases can be determined. As already described in the previous section, these shift a little from region to region. For example, midsummer arrives a little earlier in Karlsruhe than in the Ore Mountains. The Alpine area can look forward to a winter longer than the Frankfurt area. The phases are therefore mobile, which makes phenological calendars an interesting means of dividing the year. In addition, the calendar provides an insight into the indicator plants, which make a statement about the respective phase in the respective country. Many plant enthusiasts are specifically looking for indicator plants in order to recognize one of the following phases directly in nature:

1. Early Spring: Early spring follows directly on from winter and is considered the first phase of the phenological calendar. The beginning is marked by the flowering of the hazelnut (bot. Corylus avellana) and the snowdrop (bot. Galanthus). On average, early spring extends from the last week of February to mid or late March, when the last of the snow is gone.

2. First Spring: The best indication of the first spring is the beginning of the blooming of the forsythia (bot. Forsythia). The first spring lasts until the first week of May and during this period numerous fruit trees and berry bushes bloom. Cherry blossoms are typical of this period.

3. Full Spring: The characteristic indicator plant for full spring is the cultivated apple (bot. Malus domestica). As soon as you discover the first apple blossoms, winter has left the country except for the ice saints. Another indicator is the lilac (bot. Syringa), which bewitches your own garden with its fragrant blossoms.

4. Early Summer: Full spring gives way to early summer, which is characterized by numerous grasses and wildflowers. Elderflowers are also present during this period, which is mainly related to June. The high pollen levels are typical for early summer, which is not pleasant for allergy sufferers. Farmers begin harvesting hay during this time.

5. Midsummer: Directly after early summer comes midsummer, when the highest temperatures of the year are usually reached. Lime trees (bot. Tilia platyphyllos) are at their peak flowering period during this period. Currants (bot. Ribes rubrum and nigrum) and gooseberries (bot. Ribes uva-crispa) can also be harvested.

6. Late Summer: The last phase of summer is late summer. Rowan berries (bot. Sorbus aucuparia) and early apples ripen. Another harvest of hay occurs, marking the end of the seasonal grain harvest.

7. Early Autumn: A typical indicator of early autumn is the poisonous autumn crocus (bot. Colchicum autumnale). Furthermore, numerous types of fruit such as plums (bot. Prunus domestica subsp. domestica) and pears (bot. Pyrus communis) can be harvested at this time.

8. Full Autumn: The walnut harvest (bot. Juglans regia) is in full autumn. Likewise, the foliage of wild trees changes color while cultivated specimens lose their leaves.

9. Late Autumn: Late autumn leads into winter between mid-November and early December. The best sign is leaf fall from wild trees. In addition, agriculture has calmed down and numerous garden plants need winter protection.

10. Winter: Only a few species herald winter. There is mainly a long period of dormancy, which lasts until the next year's hazel blossom. Oaks (bot. Quercus) lose their foliage in this section.

The possibility of creating your own calendar for the nursery based on the phase has a long tradition. In early spring, for example, hedges and fruit trees are trimmed, while midsummer is ideal for sowing biennial plants. In many cases, a calendar based on phenology is more effective than dates, since the climate directly dictates which measures are necessary or recommended.

Notice: Due to global warming, the boundaries of individual phases can overlap or entire seasons can shift significantly. In spring in particular, many indicator plants appear noticeably earlier than in previous decades, since winters are no longer as pronounced in Central Europe.

Phenological Calendar: Reliable?

The question of whether the phenological calendar is reliable cannot simply be answered. The reason for this is the perspective. It should be borne in mind that a possible problem with the phenology is the strong dependence on the weather and other external influences. At first glance, this could significantly limit reliability if each phase is to be used to precisely determine a date. That's not the case. Up to now, phenological phases have mainly been used in order to be able to more easily chronologically classify certain phases in the cultivation of useful plants. This includes:

  • sowing
  • planting
  • harvest
  • hay cut

For these, a phenological calendar is considered to be extremely reliable, since even useful plants adapt to the climate. This means that if spring begins earlier, this can be recognized, for example, by an earlier hazel blossom. Farmers can use this as a guide and sow the corresponding types of grain earlier. In addition, extensive research on the observation of indicator plants has been carried out over the last 40 years, especially in Germany and Central Europe. Indicator plants help to recognize the extent to which climate change is affecting nature. Even as a hobby gardener or plant lover, you can therefore tell from the specific plants with a high degree of reliability whether spring is approaching or summer is slowly ending.

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Garden design