Question
Hi, my Wife has a hibiscus that is about 15 - 20 years old. It's 4 ft. tall in a 12"x 12" round container with potting soil that is at least 10 years old.It gets plenty of sun in the sun room on the south side of the house for the warmer months and comes into the house for the winter. It's doing well, growing fresh vegetation even in the winter (southern Ontario), however it stopped flowering about 8 years ago. What could cause the flowering to cease and not resume? I'd like to repot with a soilless triple mix. Is this a good time of year to do this and should I prune it back? What would you suggest? It's time this one got some TLC.

Answer
David, if the plant is getting sufficient sunlight, the most likely problems are excess water retention or insufficient nutrients in the soil.

Be sure to use a soiless mix that has sphagnum moss. This amendment helps the soil hold water, while the soiless mix will improve drainage. In short, you will need to water heavily once every 10 days or until the soil is dry 2" below the top.

You also need to feed the plant with a fertilizer high in phosphorus. Avoid fertilizers with a high level of nitrogen since these tend to promote lush foliage and very little blooming. Phosphorus is the second number in the NPK ratio listed on the front of the container. A good ratio is 10-30-10.

I hope this answered your question. Please write again if I can ever be of assistance.

Regards,

Mike