Unless I missed it I do not know in what zone you are trying to grow the lemon tree. A light frost will not hurt the lemon tree so it is best to get them outside as soon as possible. They like to bloom around January. I have one I never bring in and it handles 25 degrees with no problem. During the blooming cycle it is best if the plant is exposed to the honeybees. My lemon trees get watered twice a day for 3 minutes during the summer and 2 minutes in the winter and there is always water running out of the pot. They are on an automatic trickling system. That causes the need for more frequent fertilization (Twice a month).
Go to Lowes or Home Depot and buy a moisture checker. They are only about $4.50. Best money you will ever spend. Don't bother buying a two probe model that tests PH. They rarely work. I'm lucky I finally found one that does test soil PH and I use it all the time.
