I have a water butt set aside from the others. I put my rhubarb leaves into it when I cut a few sticks. Put the lid back on the butt and leave for a couple of days. STAND WELL BACK WHEN YOU REMOVE THE LID...the smell is rancid!!!. Give the goo a good stir and put some in an old watering can and use on brassicas. It isn't 100% effective but it sure does cut down on butterflies appreciably. Don't spill any on your clothes or HID will not be best pleased!!!
It may be worthwhile keeping a few clothes pegs near the butt to put on your nose whilst using the goo!!!
