[3] After finishing his studies, Wahlberg joined the orchestra Göta gardes musikkår, and earned money (25–50 öre per hour) by giving piano lessons.
He started by drawing landscapes, and sold a painting for the first time in 1856 to the Swedish Association of Art (Sveriges Allmänna Konstförening).
[3] The most well-known paintings Wahlberg made while living in Düsseldorf are Solnedgång i Bohuslän and Vinterlandskap med björnjakt, both of which depict Swedish forest landscapes.
[3] Almost every summer he made a short return to Sweden to study the nature in places such as Stockholm archipelago, Skåne, Halland, and Värmland.
[3] Wahlberg's fondness of romantic, dreaming, lyrical, and musical atmospheres is reflected in his paintings depicting the evening and the moonlight's play with tones and light.
[3] Among his most famous paintings from this period are Fiskläge vid bohuslänska kusten (1869, bought by Charles XV of Sweden),[4] Utsikt i Södermanland (view of a meadow and a lake in Södermanland, 1870), Landskap i månsken (landscape in moonlight, 1870), Månsken från södra Frankrike (moonlight in southern France, 1870), Nääs (a summer evening, 1871), I Vaxholm (an autumn day in Vaxholm, 1872), I Fontainebleauskogen (Fontainebleau forest, 1874), Maj i Nizza (May in Nice, 1878), Afton på Hallands Väderö (evening at an island, 1880), Fjällbacka (moonlight, 1881), and Svensk björkhage (1882).