An the busy avenue in front of the Senckenberg Museum, Julia Krohmer makes an unexpected discovery. On the sidewalk, she glimpses something green in the cracks in the stones. The herb is called small love grass, as she explains. With pink chalk, the botanist from the Senckenberg Society writes on the pavement what she has just found at the “Herb Show”. A few meters further on, the star chickweed has nested on a lamppost. It also weathered the winter well despite the recent cold snap. Around the corner, at the side entrance to the research institute, annual meadow grass, wild carrot and rocket or prostrate pearlwort, among other things, have spread along the edge of the ugly exposed aggregate concrete slabs.
The herbs often have names that are hardly familiar to the layperson – apart from dandelion or wallflower. In Frankfurt alone, around 320 grasses, herbs and mosses have been detected between the cracks and channels of paving stones and joints – nationwide there are even 500. In a book (“That grows in your city”) Krohmer together with the Freiburg nature conservation professor Alexandra -Maria Klein portrayed the “Ritzenrebellen” for the first time. 95 species are described in it.
Appreciation for herbs
With the new city nature guide, the two authors want to give the plants, which are often denigrated as worthless “weeds”, new appreciation. Because most of them provide insects with nectar and pollen. This is especially important in spring, when the herbs often bloom early. But they are also of great importance for the city dwellers. If the cobblestones are overgrown, it is easier to step on. Above all, however, the plants with their roots, which are up to 70 centimeters deep, increase the infiltration of rainwater – which helps with the increasingly frequent heavy rain. In the course of climate change, they also contribute to the cooling of urban asphalt deserts in summer. It’s up to 20 degrees cooler in the herb cracks, says Krohmer.
City herbs can not only be beautiful. Most amazed at how tough and adaptable they are. They also cannot be killed by concrete, dirt, human footsteps or dog excrement. “You could kneel in admiration,” says Krohmer. They are more widespread in public space than is generally thought. In Frankfurt, the paved areas take up around two percent of the city area, which is around six and a half square kilometers. Depending on the type, the proportion of joint surfaces in the approximately 60 different types of paving is between 15 and 35 percent – enough for habitat islands in inhospitable places.
Look out for weeds
The fact that microflora in cities has a special ecological function is a recent finding. The new appreciation for wild plants on sidewalks first began in France and then spilled over to England. Three years ago, botany enthusiasts in Germany started taking stock of herbs in a number of cities using various hashtags (#Krautschau, #mehralskraut). At that time, Krohmer went to the Mainkai with a group of helpers and searched the cracks in the pavement there, to the astonishment of passers-by. “We drew a lot of attention to ourselves,” says the botanist.
The book, published by Kosmos-Verlag, now has what it takes to become a standard work: it will be translated into English and French. The topic has also reached the municipalities. Street cleaners no longer flatten every weed. “It has changed,” says co-author Alexandra-Maria Klein. Krohmer also noticed a “paradigm shift” in her talks with the Frankfurt city administration. Awareness of the wild plants on our doorstep should be further strengthened. On the International Day of Biological Diversity on May 22nd and during a nationwide week of action from May 18th to 29th, Senckenberg once again invites you to the “Herb Show” in Frankfurt. Incidentally, there are a particularly large number of types of herbs in Frankfurt on Merianplatz in Bornheim. However, if you are a fan of the wallflower, you will have a hard time finding it. The “Cymbalaria muralis” – the scientifically correct Latin name – is mainly found in the red sandstone cracks in Miltenberg am Main in Lower Franconia.