watermelon cross pollination problem

[happyprince]

Hi,
I will grow some watermelons this year and I want to save seeds.I will grow three varieties: Blacktail Mountain,Alibaba and Gerlengech (a local Turkish variety which is extremely rare.)I have just sow the seeds of Gerlengech but Blacktail and Alibaba varieties were sown at the same time and the germination happened nearly at the same time too.
I have no other place to grow these varieties.I must grow them all in the same field.
Do different varieties have different blooming time?Do they flower at the same time?I know that Blacktail is an early variety;does it bloom earlier than Alibaba? If it does,can I be sure that these varieties did not cross pollinate?
I also plan to grow some cherry tomatoes.I heard that cherry tomatoes do not cross pollinate easily.Is it true?
any help will be appreciated,
Thanks a lot in advance...

[garnede]

You'll have to bag the blooms you want to save seed from and hand pollinate them. Then re bag till the fruit is set. Then tie a ribbon around the stem so you know to save the seed from that plant. It will work for both melons and tomatoes.

[happyprince]

thanks a lot everyone !