This week seems to be the week (the first week in July) for tomatoes to turn, especially here in the Piedmont of North Carolina. I have talked to countless people who have seen indications that there tomatoes are turning or have turned just in the last couple of days. I'm assuming if you are further North or in the mountains it might be another week or so for you. Just don't get too excited, by not waiting until the tomato fully turns, they might not be as ripe as you like. You have waited this long, what's an extra day?
If you pulled those squash or cucumbers too soon, don't fret. Or perhaps you left them on the vine too long..... well don't fret about that either.
The motto of the urban gardener should be to not waste anything. That is why it is a perfect time for seed harvesting. So cut those cucumbers up and place the seeds on a paper towel. Then wrap those seeds up in so more paper towels to help them dry. Next step, label that paper towel with the type of plant and the date using a Sharpie, and then store them in a cool dry place. I suggest a drawer in the garage cabinet. When Spring rolls around next year you won't have to spend that $1.35 on each seed packet. By harvesting seeds you will continue to have your own. You can also share them with family and friends. Or perhaps if they are pumpkin seeds you can roast them or prepare some other type of fall treat.
If you have a shredder you can shred that paper towel and use it for mulch in your garden next year too!!
By the way, take the fruit or veggies you just gored the seeds out of and place them in the compost pile for that rich soil you will use to nurture those seeds when you plant them next year.