The current UK clover varietal testing programme only conducts trials under very favourable growing conditions. This study tested commercial and experimental varieties when grown under typical marginal conditions in an upland area on nutrient poor soils. A total of 10 different varieties of Trifolium repens (AberLasting, AberDai, AberAce, Aran, Alice, AberSwan plus 4 experimental lines/varieties) and 8 different varieties of T. pratense (AberClaret, AberChianti, Merviot and 5 different experimental lines/varieties) were planted. Four replicate 6 m x 1.2 m plots of each variety were prepared in a randomized block design. Sowing rates and establishment were in accordance with the United Kingdom National List Trials, and the plots were subsequently managed using a similar cutting regime. Samples were taken towards the end of the first three growing seasons and botanical separations carried out to determine percentage biomass contribution of the sown varieties on a dry matter basis. All species showed a substantial decline from the first to third year, from an average of 55.7% to 7.9% for T. repens varieties, and 57.4% to 6.8% for T. pratense varieties. The results highlight the need to develop specific varieties adapted to low fertility conditions.