[Hortic]

Here's a dilemma. I have 'Emir' melons in my greenhouse and these and the toms are watered by a very efficient solar watering set up. They stay nicely moist on the hottest days.

But I had the misfortune to pot these up in a commercial compost that I had not used before but was available through the allotment.
Now, this compost is very free draining. The solar watering keeps the plants topped up but I have a great deal of leachate in the trays below the pots. I've a capillary system set up to drain it off with mixed success. There is a lot of liquid in some of the trays, especially under the melons. I've adjusted the watering as best as I could but that compost drains way too fast. 

Here's the problem. The melons require free draining to grow properly. But when I lifted the pots out of the leachate, the lower leaves yellowed. If I put the pots back into the leachate it could be too wet and cause a rot. Damned if I do, damned if I don't. So, can I ask if anyone has a comment on this and any recommendations? (Outside of never using that particular commercial compost again.)