Contrary to the astronomical seasons, the phenological periods are not bound to fixed dates. Yearly periods are determined by observations from nature. When, for example, the black elderberries ripen, it is time to say goodbye to summer. Snowdrops , on the other hand, initiate an early spring.
The phenological calendar consists of 10 seasons: early spring, mid spring, late spring, early summer, mid summer, late summer, early autumn, mid autumn, late autumn and winter. The flowering, fruit ripening, leaf coloring or leaf fall of certain plant species - so-called indicator plants - mark the beginning of a new phase of the year.
Snowdrops and blooming hazel bring news of early spring. Winter is over.
Around April we have first spring in our regions. It begins when the forsythia flowers and when the gooseberries unfold their leaves.
In full spring the plant development is in full activity. This season is initiated by the blossoming of the apple tree and when the stem oak develops its leaves.
The early summer usually arrives in June. The black elderberry is in bloom. This is also the time of the hay is harvested and the beekeepers hurl the blossom honey after the rape or robinia blossoms.
During this hot period the large-leaved linden flowers and the currants ripen and the grain harvest gets started.
Summer is coming to an end when early apple varieties (such as the clear apple) are ripe to be picked. Mountain ahs has also reached fuit maturityand winter rye and winter wheat are now being harvested.
Around September the big harvests are brought in. Among other things, black elderberries and cornelian cherries ripen, which signals the early autumn.
We are in full autumn when the first fuits of the horse chestnut and oak are ripe and fall from the tree. The fruit harvest is now still being completed. Towards the end of this phase, the leaves of most deciduous trees turn a red-gold colour.
As soon as the foliage of the pedunculate oak turns an autumnal colour and the mountain ash sheds its leaves, late autumn begins. The winter grain rises and soon the vegetation will come to rest.
The falling leaves of the stalk oak, the late ripening apple and the needle fall of the European larch mark the beginning of the phenological winter. Nature remains in hibernation until the following spring, even if periods of mild temperatures should occur in winter. That way domestic plants protect themselves from possible frost.
References and further information
Deutscher Wetterdienst DWD (Phenological Seasons)
MeteoSchweiz (Spring index)
Blossom of the black elderberry
Flowering large-leaved linden
Ripe clear apples
Ripe horse chestnuts
Red-gold leaves of the pedunculate oak
Bald English oak