My tomatoes have loads of yellow flowers but refuse to turn into tomatoes

I'm in Calgary , and have a green house 10 X 20 feet , I open the ends during most days , and even have a house fan to keep air blowing gently through it .
My problem is 2 years ago I had loads of tomatoes , last year I left it to nature , and this spring planted the same varieties of heritage tomatoes as before ( when I got the bumper crop).
now 45 days after getting the first yellow flower I have yet to see a tomato forming . I tried pollinating with a q-tip. and as mentioned even put a fan in the one end as I did 2 years ago.

The soil is rich in compost and the plants are 4 feet tall in some cases .
Everything is the same this year as my other year , except I have planted a lot of beets along the edge of the greenhouse , with the tomatoes more to the center.
Is it possible beets even pollination?
It sounds ridiculous , but nothing else is different .

Thanks ,Neal
 

My first thought whenever people have this trouble with tomatoes is a temperature problem. Sustained high temperatures during the day or sustained low temperatures at night can cause tomato blossom drop. I know many places it has been hot this summer — has the weather been much different than two years ago? There are other factors that can cause this too (nitrogen, humidity, etc), but temperature is the most likely culprit in my experience. Opening up the greenhouse ends should be more than enough for pollination requirements. The most I've ever done to spur pollination indoors (with no wind at all) is shake the plant a bit once a day and put a small fan on.

Tomatoes have perfect flowers, meaning they don't need a pollinator. Try thumping your flower clusters each morning. This is supposed to shake loose the pollen, resulting in better fruit set.


EDIT to add: Essentially, the same solution as Kyle. Okay, I admit it, it takes me forever to type! Cross posted with Kyle.

I hope that shaking the whole plant will work for me, as I've been doing that instead of thumping the clusters. It takes less time!

There are two things that commonly prevent tomato fruiting, to my knowledge.

Heat stress -- Sustained daytime temperatures above 85*F/29*C and nighttime temperatures above 70*F/20*C can cause blossom drop. In this case, you'll see the blossoms shriveling up along with about 1cm of stem, and dropping off wholesale. This can happen even after fertilization -- I've seen "blossom drop" happen to set fruit during heat waves. I'm not sure how you can fix this, except perhaps by leaving your greenhouse open at all times and allowing the tomatoes to cool more in the evenings. Local microclimates can affect this greatly -- I'm in central CA and our tomatoes planted in a big block and mulched thickly are still setting fruit (we've not had a daytime high below 94*F since the beginning of July). The tomatoes in the middle of the block are doing best, and when you thrust an arm into the foliage it is noticeably cooler in there. The heat of the roots seems particularly important here -- an organic horticulturalist I listen to just suggested wrapping pots in insulation material to keep roots cooler. I've not tried it, but it's an intriguing idea for potted tomatoes.

Nitrogen -- You say you fertilized the soil well with compost, but was this yard waste compost (rich in carbon) or composted manure (rich in nitrogen)? Nitrogen stimulates green growth and too much nitrogen on tomatoes yields the classic 10ft tomato vines with 1 fruit. Phosphorus and potassium stimulate flowering and fruit set. I am not aware of a way you can fix this problem within the current season.

There are a few other things that can also reduce fruiting, but I'm not as familiar with them.
Overwatering -- I've heard plant enthusiasts (maybe Mike McGrath? not sure, so don't quote me on this) suggest that overwatering tomatoes makes them think conditions are "too good" and that they should keep putting on vegetative growth and not worry about flowers until later. "Overwatering" is a nebulous term though, and depends on your soil and climate. You could play around with stressing your tomatoes out a little by not watering for a few days (perhaps up to a week if they aren't droopy in the mornings?), and then giving a deep, slow watering at the end of the wee. (Drooping/flaccid/wilted leaves in the middle of the day aren't necessarily an indicator of lack of water, but are an adaptation to deal with heat stress during the hottest part of the day. When the leaves are wilted and flaccid, the stomata are closed, and prevent further water loss by the plant.)

Lack of pollinators -- I've never experienced this, but some people swear by hand-pollinating tomatoes. Some use a little electric toothbrush (or other vibrating device) to buzz some pollen off of one plant and on to another. I suspect you could also do it with a q-tip or through the above suggestion of brushing or tapping your plants vigorously with your hands.

Good luck!

Yesterday I noticed 2 tomatoes forming on one of my Black Krim plants , maybe the result of my pollinating them with Q-tips.
The majority of my plants are Chocolate Stripe and are my favorite , I have Navajo purple ,and silver fir also ..
Thanks for the advise .