A simple, aboveground method to study cucumber (Cucumis sativus L.) root growth was developed using a subsurface herbicide banding technique. Those plants with roots that grow deeper or faster reach the herbicide sooner and exhibit herbicide injury symptoms sooner. Greenhouse pot trials showed that 0.25 or 0.50 kg simazine/ha could be used to produce distinctive symptoms; time to symptom expression increased with the depth of the band from the soil surface. Root washing experiments verified that root length was associated with response time. In field trials, response time and severity of symptoms varied with herbicide concentration, depth, and distance from the seed row, thereby providing an indication of where the roots were in the soil. About 100 diverse cucumber genotypes were tested for differences in root growth rate in the greenhouse and in the field. Time to symptom expression was normally distributed among the genotypes; analysis of variance (ANOVA) indicated significant genotypic differences. This system can be used for cultural or physiological studies, or nondestructively for selection and breeding purposes. If the herbicide is placed sufficiently deep to prevent damage to the cotyledons, the plants are capable of flowering and producing fruit. Chemical name used: 6-chloro-N, N′-diethyl-1,3,5-triazine-2,4-diamine (simazine).