Some believe that there is nothing better than a perfectly ripe tomato. Identifying a ripe tomato ready for picking can make the difference between heaven and a mulchy mess. You can't tell by color alone, particularly with heirloom tomatoes, which can be different colors (even striped and speckled). Further, you might be tempted to squeeze it to see if it's ripe, but some tomatoes are damaged if you handle them too forcefully. Here are some tips on determining whether your tomato is ready for the picking, or should remain on the vine a little longer.
Color and Shine
The first way to tell if your tomato is ripe is to check if the skin has turned from a dull, matte surface to one that is glossy and slightly shiny.
Next, check the color, which should be fairly deep unless your tomato seed packet identifies a paler color. Generally, red tomatoes should be a deep red, yellow tomatoes should be a deep yellow, etc. Further, the color should be fairly uniform; if one side of a tomato is red while part of it is still green, it's not yet ready.
Note that some gardeners harvest their tomatoes before they are completely ripe. This method can help you protect the fruit from cracking, which is more likely after a rain. If you choose this method, bring them indoors and allow them to ripen at about 70 degrees.
Feel and Texture
Your ripe tomato will give slightly to the touch — it shouldn't be soft, but rather just a little tender. Since tomatoes ripen from the inside out, this is a very good indicator. Be careful, however, to not bruise the fruit. Press it very lightly; you'll know immediately if it is not yet ripe, as it will still be quite hard.
Another indicator is how resistant the tomato is to being picked. If it hangs onto the vine for dear life when you try to pluck it, it's not yet ready. Ripe tomatoes should give way to a gentle tug.
Smell and Taste
A ripe tomato will give off a lovely fragrance, while an unripe tomato will not smell like much at all. Be careful to not confuse the tomato fruit's smell with the smell of the vines, which is almost always quite distinctive and strong.
Don't be afraid to take a taste! Veggies grown in a home garden are not as flawless and may not be as large as those you are used to purchasing in the supermarket, so you may not be familiar with a real, ripe tomato. Tasting a single tomato on your vine should leave you with many more to pick later — and can prevent letting your tomatoes remain too long on the vine which will just result in rot and splitting.
Tips on Harvesting
Once you start picking your tomatoes, be sure to check your tomato patch daily. Birds or other critters will be paying close attention to your beautifully ripe tomatoes, and the fruit will begin to fall off the vine when it is too ripe — so get them before you lose them.
If you're growing heirloom tomatoes, pick them just shy of full color, because they generally ripen before the color deepens.