ABSTRACT. The goal of our study was to improve 'Tannat' grape and wine composition, by achieving vine balance. We evaluated a new grape-growing paradigm for Uruguayan conditions that include unpredictable periods of water deficit or excess in nonirrigated vineyards and eliminates competition from cover crops. We used undertrellis cover crops (UTCC) to limit vine water availability, reduce vine growth rate and final canopy size. However, to avoid excessive vine water stress due to the UTCC competition, irrigation was used during water deficit periods. This strategy was tested in combination with variable planting density to optimize vine vigor control in our environment over two growing seasons in southern Uruguay. Two factors were evaluated in a split-split plot experiment with five replicates. Treatments were:UTCC (full cover of the vineyard soil with tall fescue) versus conventional alleyway tall fescue with 1.0 m wide weed-free strip under the trellis, and two spacings between vines (0.8 vs. 1.5 m). Deficit drip irrigation was provided at mid-day stem water potential (SWP) thresholds of -0.9 MPa early and -1.1 MPa later in season. Shoot growth rate, SWP, berry size and berry composition (Brix, organic acids, total anthocyanin) were monitored over the season as well as final yield, cluster and pruning weights. Preliminary results showed that UTCC regulated vine vegetative growth and final canopy size, reduced berry size, cluster weight and bunch-rot incidence as well as increased tartaric/malic ratio, Brix and anthocyanin concentration in grapes. The combination of UTCC and 1.5 m inter-row spacing led to below-optimal shoot growth. The use of such multiple techniques shows promise for achieving vine balance in high-capacity conditions. © 2017 ISHS.