Polymers
Polymers are chemical compounds created and designed to save tremendous amounts of water.
When these polymers or polyacrylamide crystals are used in the soil at planting time they can absorb 200 to 300 times their weight in water. They will hold it in the root zone where the plant then can use it. These crystals will turn to gel when they absorb water and nutrients and then will provide the plant with a consistent supply of water even through great periods of drought.
Polymers can also improve the structure of soil by expanding and contracting. Through this, the gel will absorb and release water. This very action increases air spaces in the soil which the plant roots need to exchange oxygen and carbon dioxide.
They are safe to use and classified by the EPA as non-hazardous.
When planting containers, polymer crystals may be used by first pre-moistening them and then mixing with the potting soil. About one part expanded granules to six parts soil. Then plant in the container as usual making sure there is good drainage. You may even mix the polymer crystals with a fertilizer solution prior to adding the soil and it will provide a time released source of nutrients.
Crystals may be used in an existing container by poking holes with a pencil to about 2/3 the dept of the pot and pour in a small amount of dry crystals. For a six inch pot four holes will do. For an eight inch pot, six holes, and for a ten inch pot about eight. Use one tsp of dry crystals for the ten inch pot.
Subsequent watering should be made at about one half the frequency of untreated soil.
There are several brands on the market.
Always read the label for specific instructions.