The palms are inseparable part of Polish culture and tradition during Easter time.
They are made using traditional materials such as: desiccated flowers, grass, corns and herbs. Those on the photo are from the Lublin region.
These substitutes were used in place of real subtropical palms, which were never easy to obtain in Poland.
See this link for more information about Easter Palms in Poland http://culture.polishsite.us/articles/art274fr.htm