There are two types of fertilizers: timed-release and water soluble. Both
are needed for container vegetable growing success. Slow or timed-release
is added at planting time, and should be thoroughly incorporated into the
soil mix. Look for a complete, balanced type such as a 10-10-10, 13-13-13
or 14-14-14 formulation. Osmocote® in a 14-14-14 formulation is just
one example of a slow-release fertilizer that can be used. The ratio of
this fertilizer to soil mix is 1/2 tablespoon of fertilizer to one gallon
of soil mix. Thus, a 3 gallon container would need 1 1/2 tablespoons of
fertilizer, a 5 gallon would need 2 1/2 tablespoons, and so on.
Water soluble fertilizers are added about mid-season when the plants
begin to produce. This additional fertilizer is needed because most potting
mixes don't retain nutrients very well, the plant's roots are restricted
and thus somewhat stressed, and watering leaches nitrogen out of the soil.
Peters® 20-20-20 or Miracle Gro® 15-30-15 are just a couple of
the water soluble types that work well for container gardening. Some experienced
container vegetable gardeners have success with a "super bloom"
type of fertilizer, one with a high phosphorus content to stimulate blooms
and subsequent fruits. If you want to experiment with this type of fertilizer,
look for a 10-50-10 or 19-59-9 analysis. These water soluble fertilizers
should be mixed at a slightly weaker rate than the label recommends and
added once every week or two.
Since potting mixes drain water rapidly, fertilizer will be washed out
of the container as you water. Lighter mixes will require more frequent
fertilizing than heavier mixes. It's a good idea to use a dilute liquid
fertilizer with every other watering. Liquid fish emulsion or liquid seaweed
are great plant boosters, but remember that you need to provide your plants
with a variety of nutrients. Check the labels on the products in you garden
center to be sure that they contain a complete, balanced solution that
includes trace elements.