Specialty Gardening: Balcony Planters, 1 by andycdn

andycdn wrote:
If you want to try the Watersorb crystals, there's a co-op going on here on DG at http://davesgarden.com/forums/t/698140/ They can really be a lifesaver for your plants in hot weather.

These are polymer crystals that you mix (sparingly) in the soil and they absorb water and swell up into jelly-like pieces. As the soil dries out they release the moisture to the plant roots. You can get away with watering less frequently. I use them at the cottage so my planters are usually safe for the week, and at home on the decks in boxes that would otherwise need watering twice a day.

This photo shows a balcony-railing planter with sun-loving subjects that survived a pretty hot summer with these crystals in the soil. They're good for patio tomatoes, too, which prefer even soil moisture.