Once a week is still too much-i have a nobile that has survived one once a month! You're in the states? I think about now would be the time to start, and then as soon as new growth activity starts, go for it! Start with a light growth inducer fertliser (high Phosphorus i think), and then after a about two months, switch to a light tomato fertiliser, these are high in potassium and are cheap! Either that or water with one or two grains of Potassium Permanganate (potash) dissolved in abotu a litre or two of water. One grain is usually enough for 1.5L