Never start from seed if you are anxious to see your fruits grow.
Go ahead and set aside a thermometer to measure your soil or substrate temperature in your growth medium.
Keep a current measure of the temperature in your root growth medium.
Remember that you can expect to see leaves falling off just about any Lemon tree, no matter the size or age, at 60 degrees F or less.
Trees missing leaves are sure to require more time to flower and fruit.
Your choice of the growth medium substrate will affect water holding capacity and drainage characteristics of the root structures of the tree.
The following lighting alternatives are available and may surprise the grower with the lemon tree growth success assuming all other other growth requirements are ideal: 1) Fluorescent 2) HPS bulbs 3) MH bulbs
My family has grown lemon trees for generations and after years of trial and error and reviewing current agricultural studies for optimal fruit production it has been definitely proven that lemon trees will bear optimal fruits if the root substrate achieves close to 80% nutrient solution when allowed to drain at gravitational pull at field capacity or pot container capacity.
Clonex Gel works great as a professional root hormone gel to help insure saturation of root structure for hydroponic lemon tree systems.