Robellini's are a little sensitive to the cold, although Tampa has been spared this particular winter, other than a cold night a couple of weeks ago. I covered mine with a frost blanket. Your concern sounds more like a fertilization issue. Palms need a different fertilizer than your regular landscape plants. I feed my palms regularly every three months with a palm fertilizer and added doses of epsom salt. There are trace elements they need that are not as prevelant in regular shrub fertilizer. They are all a deep green and healthy. Palm spikes are okay, but I prefer scattering the palm fertilizer completely around the trunks of the palm. I extend it out 12 to 24 inches depending on the size of the palm. Hopefully that will correct your concern.