Seeds of Artemisia annua L. were produced by Humber VHB (Chichester, UK) in a glasshouse in winter 2006/07 and pelleted with a specialist vegetable pellet and sown and grown individually in 2.5-cm _ 2.5-cm and 3-cm-deep modules by Frontier Agriculture Ltd (lot B/2007). Six hundred individual seedlings of A. annua were transferred to East Malling Research, where the plants were subsequently grown. In late June, 400 seedlings were selected and potted into 7.5-L pots using Klassman medium Irish graded peat with no added N, P or K, to which 1.9 g of CaCO3 per litre of peat was added to raise the pH to between 5.8 and 6. Chemical analysis of the compost revealed that concentrations of N, P and K were respectively 30, ,0.6 and 5.3 mg L21 of compost. Plants were placed in a naturally lit unheated glasshouse for 3 weeks to establish. They were then sorted according to size and placed outside onto a freely draining gravel bed (11 _ 4.8 m) in 15 rows, on 19 July; the pots were staggered along the row, with 20 pots per row. Rain infiltration was excluded from the pots, which were covered with plastic. Plants at the end of each row acted as experimental guards; each experimental block was guarded by a complete row north and south, removing edge effects from the experiment.