Urban green spaces with healthy vegetation play a key role in improving the quality of life in cities. However, urban soils, the basis of the urban greenery, are under strong anthropogenic influence and can considerably differ from natural soils. In this study, we observed short-term greening and browning of lawns during one vegetation period in urban parks of Geneva (Switzerland). We related the temporal trajectory of seasonal Normalized Difference Vegetation Index (NDVI) (8 days median) as a proxy of vegetation condition at different test sites to the physical soil properties (soil depth, coarse material, bulk density, conditioned air and water content) and Soil Organic Carbon (SOC). Strong drops of NDVI during dry periods in summer were related to shallow soil depths (<40 cm) and a high amount of coarse material (>10%) as well as lower SOC. Bulk density of the fine earth and the soil structure quality (expressed by air and water content of soil cores conditioned at a soil water potential of −100 hPa) had a significant influence on grass growth in spring but not in summer. Dense soils with conditioned air content closer to the trigger value of degraded soil structure resulted in lower NDVI values in spring. Our approach of using Earth Observation (EO) data for observing short-term greening and browning patterns, in this case the rise and decline of NDVI values, revealed that the role of the soil properties changed with the season. This approach may contribute to digital soil mapping and the assessment of soil ecosystem services in urban contexts. Urban planners are advised to save natural soils from over-building and keep them for green spaces. If soil has to be restored to create new green spaces, it should be deep and should not contain much coarse material, even for grassy vegetation.