Published in the
Contra Costa Times on
Q. I have always placed a little gravel in
the bottom of my pots to improve the drainage. A gardening friend of mine told
me this is not a good idea. Why? How often should my plants be re-potted?
A. One of the most durable gardening myths
is that placing rocks in pots somehow helps the plants. Your friend is correct;
you
do not need to put anything in your pots except a good potting soil and your plants. If potting soil comes out of the drainage hole in the pot, place a small piece of screen over the hole to help hold the soil in place. Rocks and pebbles in the pot simply reduce root room and can actually increase the chances of root disease occurring since they impede rather than facilitate drainage.
The frequency of re-potting depends upon the plant. Plants
in containers should be repotted when their roots have filled the container,
which in an actively growing plant may occur frequently. Slower growing plants
will need to be repotted less often. Re-pot plants into slightly larger containers,
with fresh potting soil. A good potting soil will hold moisture, be well
aerated and slightly acidic. Select a mix with a high percentage of bark or
forest products of sphagnum peat mixed with vermiculite or perlite.
Leach the soil well prior to planting to reduce soluble salts. Some plants will
need specialty mixes, for example cacti need a sandy mix with less organic
material. If you are re-using pots, clean the pots well before replanting. Clay
pots in particular tend to accumulate salts, giving the pots a whitish bloom.
Soak the pots and scrub off all visible deposits before replanting. Salt
accumulation is a frequent problem with container plants. The salts tend to
accumulate in potting soils, a result of fertilizing and improper watering techniques.
Plants in containers should be watered until the water drains out of the
drainage holes, but plants should not sit in that water. The salts dissolve and
create a concentrated solution which if allowed to remain in the saucers is
reabsorbed by the plant roots. Plants vary in their sensitivity to salt damage,
and some seem to show damage regardless of the level of care. Spider plants are
notorious for having brown tipped leaves. The signs of salt damage include
reduced growth, leaves with brown edges or tips, leaf drop, small new growth
and dead roots. Plants should optimally be watered in a sink or outdoors where
the excess moisture and salts can drain away. Houseplants should be leached at
a minimum every 4-6months.