Standard-sized tomatoes take 20 to 30 days from blossom set to reach full size–commonly called “mature green”; they take another 20 to 30 days to ripen, that is begin to change color. A tomato can be picked when it begins to change color–from green to red, pink, yellow, or orange depending upon the cultivar.
The optimal temperature range for tomato ripening is 68°F to 77°F; tomato ripening is slowed when temperatures are cooler or warmer than the optimum range. Tomatoes stop ripening when temperatures are less than 55°F and greater than 85°F. Once a mature green tomato has begun to blush or turn color, it can be brought to full color or full ripeness off the vine at room temperature–70°F to 75°F. A tomato will be equally flavorful brought to full ripeness on or off the vine–once it has moved beyond “mature green” to color change.
Estimated days to maturity, fruit size, and color can be used to estimate the harvest time for your tomato crop. Temperatures outside the optimum range can delay harvest. Tomatoes can not be forced to maturity more quickly than nature will allow. However, there are to expedite the tomato harvest when temperatures are right.
Once tomatoes on the plant begin to reach mature green, here’s how you can quicken the overall ripening of fruit on the vine:
• Harvest daily. Pick fruit as soon as it starts to show color; this will allow other fruit on the vine to gain size and come to harvest more quickly. Tomato fruit picked at first sign of color can be ripened at room temperature. Fruit ripened off the vine will be just as tasty as those left to mature on the vine. Cut or gently twist off fruits supporting the vine at the same time. Don’t leave overripe fruits on the vine; they decrease productivity and may spread disease.
• Remove flower clusters. Pluck new flower clusters from tomato plants that have already set fruit. Removing flowers will direct the plant’s energy into ripening the fruit already maturing on the vine. Remove flower clusters no later than a month before the first expected frost to ensure fruit on the plant makes it to harvest without frost or cold damage.
• Remove small or excess fruit. Pick small or excess fruit off of the tomato plant. Removing immature fruit or fruit you will not use will allow the plant to divert energy into ripening larger, already maturing fruit. Tomatoes that reach “mature green” size and have their first blush of color can be ripened off the vine at room temperature.
• Remove some leaves. Pinch away suckers and lower leaves. Tomato plants almost continuously produce new shoots–called suckers–between the main stem and lateral branches. Pinch or prune away this new growth so that the plant can channel its energy into producing and ripening fruit rather than producing new leaves. Leaves just above fruit or fruit clusters should be left in place to protect fruit from sunburn, but leaves low on the plant and yellow, brown, or diseased leaves should be removed. These leaves are taking energy away from fruit ripening.
• Reduce water and food late in season. Reduce water and fertilizer to encourage “mature green” fruits to ripen. Fertilizer–especially excess nitrogen–encourages new leaf growth at the expense of fruit growth and maturation. (Use fertilizer low in nitrogen 4-8-4 for tomatoes.) Reducing water as fruits reach mature size will enhance ripening (and concentrate flavor) and direct the plant’s energy away from new fruit set to ripening fruit already on the vine
• Stress roots near season end. Shifting or rotating plant roots by twisting gently at the crown of the plant will disturb distribution of nutrients and moisture from roots to fruit and foliage causing the plant to finish fruit growth, ripen, and go to seed.
• Protect plants from extreme temperatures. Shield plants from temperatures outside the optimum range; wrap cages with clear plastic or frost blankets to protect plants from temperatures below 60°F; drape shade cloth over frames to protect tomatoes from harsh sun and temperatures greater than 90°F. Temperature extremes will slow and even halt fruit maturation and ripening. If fruits have begun to turn color, pick them and finish ripening indoor at temperatures between 70°F and 75°F.
• Mulch with plastic sheeting. Use silver- or red-colored plastic sheeting or aluminum foil to speed growth where temperatures are low or days are overcast. The light reflected from colored plastic or foil stimulates the movement of carbohydrates into developing fruit resulting in early plant ripening by a week or more. Place a colored tarp under plants or secure the tarp to posts and stretch the tarp along the north side of the tomato bed or row.
Slow to harvest regions. In regions where tomatoes are consistently slow to ripen, here are general tips to speed the harvest every year:
• Early to mature varieties. Grow tomato varieties that require a shorter period of optimum temperatures. Quick-to-harvest tomato varieties that require 55 to 70 days from transplanting may be best suited for regions where temperatures do not stay in the optimum range long enough to ripen fruit.
• Plant earlier. Start tomato plants indoors and begin to harden off plants four to five weeks before the last frost. Move seedlings into the garden about three weeks before the last frost date. Set them into the ground an inch or so deeper than they were in their cartons and water them in. Place cloches or tomato cages wrapped in plastic around these transplants and protect them from low temperatures until night temperatures are consistently greater than 55°F.
• Keep plants warm. Where nights are cold, place self-standing sleeves or water around plants or flank young plants with flat tiles that hold the sun’s heat during the day and radiate it at night. Plant tomatoes near a wall or the side of a building that faces west or south. The wall will soak up the sun’s heat during the day and radiate it back out at night.
• Stake or cage plants. Support tomato vines with a stake or cage. Grow plants up exposing fruit to sun and air.
• Ensure pollination. On warm, calm days give flower clusters a little shake to aid pollination. Cool, wet weather or hot windy days can inhibit pollination. Blossom drop happens when flowers are not pollinated; where pollination does not happen, fruit will not follow.