A healthy, mature, Aloe Vera will bloom (flower) when it's ready...
Which translates into -- as far as I'm aware you can't "force" an Aloe Vera plant to bloom, it will flower once it reaches maturity (roundabout 4 years old), is in good health and has stored up enough energy to-do-so.
Below are some points which will help keep a potted Aloe Vera plant in good health:
Container/Pot should have drainage holes.
Size of the container/pot should be suitable for the size of the plant ie Aloe Vera doesn't mind being a little bit root-bound.
- When repotting move up one pot size; early Spring is the best time to repot.
Potting medium should be free draining, either use a "Cactus" potting mix or add some additional "Perlite" or "Coarse Horticultural Sand" or... to a soil free potting mix.
Minimal water during the Winter.
Water thoroughly (saturate), then allow the potting mix to dry out between waterings during the growing season.
Keep in a bright, well lit spot, but out of direct sun-light (especially important during the heat of Summer).
Best not to subject to temperatures below 50°F (10°C).
Most definitely do not want to subject to "light" frost temperatures or anything below 32°F (0°C).
During Winter try to keep the temperature between 50 to 60°F (10 to 15°C), doing so will give the plant an opportunity to "rest".
I fertilize it with tea from my vermicomposter
Q. How much and how often?
A. I give it diluted dose of vermiicompost tea in almost every watering.
You're more than likely overfeeding it. One feeding per month during the growing season would be more than enough (IMHO).
It is in rich garden soil in a ten inch pot. I heard that this is the right size to start flowering.
Q. Please describe/explain "rich garden soil"?
A. The soil is good, dark, crumbly garden soil that grows plants very well.
That is not the ideal growing medium for an Aloe Vera. Why?
It will not be free draining enough ie The soil will retain too much moisture while it's drying out.
Refer above for recommended "potting medium".
When I said 'I heard this is the right size to start flowering', I was actually talking about the plant, not the pot.
Pot size has no bearing on flowering (refer to initial statements above).
Oops! ok my bad, I read it wrong...