aa2by2 said: 
thanks for all your responses. i have decided to cut the stalk two feet from the soil and replant the top part.
another issue: sometimes after i water my corn plants a number of leaves will turn brown....i am guessing this is root rot from overwatering?
so could overwatering be prevented by putting in an inch or two layer of stones/pebbles/perlite at the bottom of the planter?
The main problem with overwatering is that too much water is retained in the pot instead of running out the bottom. Water displaces air, but oxygen and CO2 won't diffuse through water in soil voids as fast as through air in those same voids - gasses diffuse 10,000 or 100,000 times faster through air than through water.
Too much water is retained for two main reasons: perched water and capillary water.
The soil usually holds too much water because the soil is too fine-grained and not coarse enough.
Peat-based potting soils are like deathtraps if you tend to overwater as I do! Look for grit, crushed stone, bark chunks or coarse Perlite.
Capillary water clings to soil particles in a thin film. If the soil voids are as small as twice the thickness of a capillary film, they fill completely and HOLD that water, displacing air and drowning the roots. Small soil particles casue small open spaces. Coarse soil particles cause larger open spaces.
Perched water happens when the soil changes abruptly in coarseness or composition. For some reason, capillarity works better with "like to like" soils. When fine grained mixes sit on top of coarse gravel or pebbles, the water reacts as if the abrupt transition was impervious to water. the "capillary connection" breaks when you put stones, garvel or broken pots int he bottom of a pot.
That's an example of conventional wisdom that is dead wrong.
In containers, the whole batch of soil should be uniform and coarse enough to [b]drain quickly[/u]
The solution is a coarser soilless mix from top to bottom and specifically spilling out the drainage holes. If the soil can touch whatever is UNDER the pot, the water can be pulled by capillary attraction right out of the pot (especially if you set the pot down on something that wicks, like a cotton towel or flannel. (Like this, but with a bigger pot:)
http://garden.org/ideas/view/R...
Al / Tapla convinced me that soil mixes coarser than around 0.1" are ideal for containers. They drain fast enough that you CAN'T drown the roots, but you might have to water every day since the pot does not hold a lot of water. Instead, it holds a lot of air, which lets the roots breath!
