Figure 1.

Pot set-up. We filled 1-L square pots with a 1:1 mixture of fine sand and fine vermiculite, and placed PVC barriers in the pots to create four pot quarters. The middle 2 × 2 cm was left open. We supplied plants with a 40ml nutrient solution three times a week with four syringes in the depicted spots (160 ml in total). Plants in the heterogeneous treatment received a high-strength nutrient solution (40 ml 1/2-strength Hoagland solution) in one quarter and a low-strength nutrient solution (40 ml 1/64-strength Hoagland solution) in the other three pot quarters. Plants in the homogeneous treatment received the same total amount of nutrients as in the other treatment but as equal intermediate-strength nutrient solutions (40 ml of ~1/8-strength Hoagland solution) in all four pot quarters.