Gardeners Supply I have used the gallon size successfully in a 28" pot, in your case it will require repotting. If you go this route you might be able to trim the roots a bit (not sure of your plant type). If you water the plant well before you put a spike in you can also/or use a terracotta spike which won't flood the soil. Terracotta Plant Watering Stakes. I use a combination of these 2 for our lake house (which we might not see for a month at a time). Regular or 1.5 liter wine bottles work better that 2 liter plastic.