You might want to research the allelopathic properties of sunflowers. Your plan would normally be considered detrimental to the tomato plants. Put the sunflowers in their own section of the garden away from any other crops.

Plus in your zone, why such late planting for your tomatoes?

Dave

Well I have no other spots for the Sunflowers and I have read on how people use them as supports. I assume those people would be planting them inches a part, where as I'll have them 1-1.5' a part.

I started them late again, for some reason I always do that. But last year they did great. I got them growing to about 10'. But those seeds were taken from a grocery store tomato. Hopefully they will do just as good. But like with any garden its really a experiment to see what works.

Since I'm experimenting I could always divide the crop in half and do one section the way I described above and then the other half put nursery pots into the ground and plant the sunflowers in those. That way I can see which crop has a higher production.

If you are in an area that gets days of over 100 degrees then planting them on the south side of the tomatoes may be of some help. I know they say tomatoes should grow in full sun. In areas that get over 100 if something is on the south end to give a bit of shade in the evening it can help tomatoes. The two plants that gave me the most tomatoes last year were shaded in the evening. The plant was still getting 10 hours of direct sunlight.

I think, as long as their(sunflowers' and tomatoes' ) roots do not get tangled up, it should be fine. Probably 1.5 apart is good enough.