There aren’t a lot of gardening stores in the city center, and you will not find much like this in the market hall. You might find some in Hermes by Keleti Railway station (Baross tér 16.), but to be sure, I’d rather visit one of the OBI stores in Budapest (in Köki Terminal, the end station of blue metro line), or the one by Savoya Park (end station of tram line 18).
There are also 100% gardening stores such as Fitoland and Oazis that you can search for in Google Maps.