Growing two sweetcorn varieties together

I don't think you can grow them together. You eat the seeds so cross pollination matters

Thompson and Morgan says
CAUTION: Extra Tender' corn can be grown with 'Super Sweet' varieties, but isolate from 'Sugar Enhanced' types as they will go starchy.

So you have to find out which types these are.

Another option is to temporally separate them - sow whichever is the quickest to mature first then sow the other a couple of weeks later so that the first will have been harvested by the time the tassels on the second are appearing

Usually, you only have to be concerned about cross pollination if you're saving seed for growing next year. With chillies for example, cross pollination doesn't affect the pods, just the genetics of the seeds inside.

Sweetcorn is different, and I haven't really understood it completely, but it's something to do with cross pollination (but only in some combinations, depending on the varieties) causing the corn kernels to become more starchy rather than producing the plant sugars that give the sweeter taste.

I think the 'standard sweet' and 'sugar enhanced' varieties are ok, and can be grown together, but the potential problems are with the newer 'supersweet' varieties, which need to be grown separately.

The 'supersweet' are also thought to be harder to germinate and grow, especially in the cooler conditions found in most of the UK, although there are varieties that are supposed to cope better with our climate. There's one variety called 'Northern Extra Sweet F1' which somehow would be more amusing if they'd called it 'Extra Sweet for Northerners F1'

The seed companies aren't always as helpful as they could be in making things clear, and which varieties need to be grown separately, and which can be safely grown together.

Descriptions like 'Tendersweet' and 'Extra Sweet' also muddy the waters.

Yes, grow them as far apart as poss, and also try sowing them at different times, so hopefully pollination will occur at different times.

The Double Red if it pollinates the yellow corn, will result in some red kernels in amongst the yellow kernels, and could affect the taste.

sweet_corn

If you grow Double Red (su) and Sparrow F1 (I think sh2) together at the same time, you will end up with some starchy kernels, the amount will depend on the degree of cross pollination. From previous experience this can be a real disappointment and rather than delicious scrummy cobs, they can end up tough as old boots and fairly tasteless. As suggested you can try growing them apart distance wise and or staggering their sowing time.

If you do decide you want to save seeds from Double Red you will need to grow out a large number of plants in isolation as sweet corn suffer from inbreeding depression. They are wind pollinated out-crossers and most often it is recommended to save seed from a minimum of 100 to 200 plants. Although you can save seed from less plants if you hand pollinate.

Thanks everyone for the advice!

Foolishly I sprouted them both at the same time but I'll do my best to keep them apart- I'll stick the Double reds down the end of the allotment and keep the sparrows in the back yard if I can squeeze them in somewhere.

Cheers!