Hi Russ - it's all about feeing the soil and creating humus, as small boxes provide limited access to nutrients (even using good quality potting mix) because they get eaten up so quickly by the hungry plants. a worm farm or compost are perfect so you can feed the soil regularly each week as natural fertiliser. also - are the boxes draining from the bottom? when you water, the nutrients run straight out the bottom and the plants cant access them. You can build really simple self watering containers in old broccoli boxes... punch a few holes along a horizontal line, about 1/4 from the bottom of the box. then fill to this line with pebbles or gravel - this creates a water table where water will sit and if too much water is added it spills out through the holes. put the soil on top with lots of compost and worm castings, plant your vegies, and then mulch on top. this system allows the roots to reach water at the bottom, but stops the soil from being water-logged. it also allows you to mulch and build humus within the soil without draining it all away. I even water at the edges of the box so that the water goes straight to the water area without disturbing the humus to stop any nutrients draining away. i hope this makes sense! I read Jackie French's Soil Food Web book which was also really helpful. good luck!

- Catherine