Expert: Long Island Gardener - 5/25/2008

Question
The hibiscus plant I purchased a month ago has been producing large deep colored blooms and very plentiful. As of the last three days, the blooms are smaller, paler and the leaves are turning yellow at the bottom. Thank you for any info.

Answer
I guess we can assume this is a tender, Florida-loving Hibiscus?  A hardy Hibiscus would be going dormant as we speak, accounting for Yellow leaves.

We have to know before we can proceed.

Tropical Hibiscus has glossy deep green leaves and, often, huge flowers.  They can be vivid scarlet, magenta, yellow, white, eggplant
violet; they can have double or single flowers.  The common hardy Hibiscus has very large buds, sometimes they even have large flowers, up to 6 inches wide.  But they don't reach the dinnerplate-sized blooms of the tender tropical Hibiscus.

Your data regarding "Ounces of Water" indicates you are monitoring this patient...er, this plant with medical precision.  I am impressed.  I don't recall ever seeing anyone outside of a research laboratory this careful about routine houseplant care.

Assuming now that you have a tropical Hibiscus, hardy to USDA Zone 9 and south, bear in mind that Hibiscus are thirsty drinkers and aggressive feeders.  Without knowing the size of the pot, and the root system, I can't tell you if that water is too much or not enough.  Room temperature water spiked with a little fertilizer every time you water should SOAK the plant.  Use a deep dish underwater tray instead of the usual shallow saucer; water until the runoff fills up the tray, then wait and see if it is soaked back up into the pot during the next 15 minutes.  If it is, that's how much you should water the next time the pot is nearly dry.

Use either a balanced fertilizer (20-20-20 or 10-10-10) or one highest in Phosphorous, which promotes flowering (10-20-10 or 5-20-0).

Don't water too much, either.  If you do this every day and the plant is not having a chance to dry out, cut back on the schedule - but not on the amount of water/fertilizer.  Any watering should DRENCH the pot.

That goes for pretty much every potted plant, from Orchids to Philodendrons.

Hibiscus are finicky to begin with.  They don't like any change - simply turning the pot to face the window to keep the plant from bending can make them drop leaves and buds and sulk.

And since it's Winter, the flowering and growth cycles slow down anyway.  Remember, these are tropical plants - used to consistent 12-3 hr  day lengths.  Get down to 9 or 10 daylight hours a day and they know something's up.  Yellowing, and dropping, of leaves is their way of saying I'm mad as hell and I'm not going to take it anymore.

Low humidity, however, they can take reasonable doses of.  The more humid the better.

Recap:  Water bigger but less often; spike with fertilizer (and don't overdo the fertilizer - you don't want to burn any roots here); and provide consistent humidity and temperatures.  No cold showers or  cool breezes for this plant.  EZ does it.

Let me know how it goes.  If this is a perennial, hardy Hibiscus, we will have to forget all of the above and start over.

THE LONG ISLAND GARDENER