Two experiments related to the use of Gliricidia sepium in alley farming are reported. Evaluation of early vigour and mulch yield of a Gliricidia germplasm collection from Costa Rica indicated that the collection contains significant variation for both characteristics. Over four harvests, the four highest yielding accessions produced 37% more mulch than 'Ibadan Local'. Six planting densities were established with seedlings to determine their effects on mulch yield of Gliricidia. With more than 12 seedlings m-1, the percentage of seedlings which successfully established was reduced. Over four harvests, the greatest mulch yield was obtained with approximately 10 established trees m-1.