Hot-House Tomatoes Not Setting Fruit – What’s Wrong?

Q.  I have a hot house in the back yard.  I built a planter and filled it with soil in which I added horse manure. I planted six or so tomato plants about 4 months ago. I put both mh and hps grow lights in and keep the room in the 70’s. My plants are huge but there is no sign of fruit. They are feed and watered and have grown up to the roof, they look healthy, they have flowers but don’t seem to have the little bulb with them that turns to fruit.  My goal is to have tomatoes all year around, but now our out door tomatoes have passed up my attempts to grow in the hot house. Can you help me, I’m new at this.  Can I be running the grow lights too much?
 
A.  Do your tomatoes get any sunlight, or is the light source only the grow-lights?  Tomatoes need real sunlight all day long in order to produce fruit, so if anything, they are getting too little light, not too much. 
 
What are you feeding them?  A balanced mix of natural minerals is what they need.  4-month old horse manure has long since used up its nitrogen, since nitrogen is volatile, and goes out into the air or the water fairly quickly.  And both phosphorus and potassium fairly quickly become fixed, or unavailable to the plants, by adhering to the soil particles.  Use the Mittleider Weekly Feed mix, fed just that way, and you’ll have healthy, productive plants.
 
And finally, is there any air movement in the hot house?  Tomatoes are self-pollinated, and in the garden, where there is some air movement from the breezes, they don’t need any help to pollinate.  However, in a still greenhouse, it may be necessary to vibrate the stems two or three times each day, to help them pollinate.