Growing tomatoes can feel like a gamble sometimes… To top off or not to top off? Do I top off now or should I wait another week or two? Will the cold weather hit earlier or later than predicted? Will day time temperatures keep the soil warm enough? How do I best avoid a frost-bitten crop of half-ripened or completely green fruit when the weather turns cold?
Getting the most out of your tomato crop means knowing if, when, and how to top off your tomato plants. This requires having a sound understanding of the ripening process as well as your local climate.
What is Topping Tomato Plants
Topping is a type of pruning that is done towards the end of the season to remove any flowers and growing tips. This is common in temperate climates to divert the plants’ energy into the remaining fruit in an effort to ripen them before the cold weather arrives.
Why Topping Your Tomato Plants is Necessary
As the weather cools and the season draws to an end, any flowers remaining on the plant will have neither enough warmth nor enough time to develop into mature fruit, so they should be removed so that the plant focuses its energy on the remaining fruit. The primary purpose of topping is to accelerate fruit ripening in preparation for the final harvest before the frost kills the plant.
In temperate climates, topping your tomato plant is pretty much essential unless you are growing in a greenhouse or indoors. The only exceptions to this are determinate or ‘bush’ tomatoes, which have a very short flowering and fruiting period anyway.
Factors Affecting Tomato Ripening
Since the reason for topping off tomato plants is to speed up the ripening process, then it’s necessary to understand what factors affect fruit ripening.
- PHOSPHORUS: Encourage fruiting with a high phosphorus fertilizer throughout the fruiting period and immediately after topping the plant, but withholding fertilizer 3 – 4 weeks before the cold weather strikes can actually hasten the final ripening.
- WATER: Withholding or reducing water 1 – 2 weeks before the first frost can also speed up ripening and may help to keep the soil warmer.
- VARIETY: Heirlooms and larger varieties of tomatoes may take up to 65 days to ripen after flowering compared to smaller ones like cherry tomatoes, which may only take 30 days after flowering. Indeterminate varieties continue to grow, flower and fruit as long as the weather permits, so they need to be topped when cooler weather is predicted.
- TEMPERATURE: Both soil and air temperature affect tomato ripening. Flowers won’t develop and fruit won’t ripen when overnight temperatures drop below 55 °F (13 °C). A frost will kill most tomato plants and prevent ‘breaker’ tomatoes from ripening properly. Sunlight will make the skins thicker so place them in a dark cupboard or cardboard box with ventilation to ripen.
- GROWTH STAGE: Tomatoes that are harvested while still white or completely green won’t ripen, but tomatoes that have a hint of red color (called ‘breakers’) will slowly ripen at room temperature in a ventilated box, as long as they haven’t been out in a frost.
How to Top Off Tomato Plants
Simply look for any flowers and cut them off the plant, including all of the vegetation above the flowers. New growth can also be removed and even white fruit can be removed, depending on when the cold weather is predicted.
When to Top Off Tomato Plants
In most cases, your tomato plants will survive one or two nights below 55 °F (13 °C), but a weeks’ worth of cool weather on the monthly forecast can help to determine when to top off your tomato plants.
This leaves the plant about 3 – 4 weeks after topping for the remaining tomatoes to ripen before the cooler weather hits. For larger or heirloom varieties, the old farmer’s almanac can provide a predicted date of the first and last frosts for each year, and topping flowers on these varieties should be done about 6 weeks before this date. And if all else fails and you lose the weather gamble, simply pull the entire plant out of the ground before a killer frost and hang the whole plant in a shed to allow the fruit to finish ripening on the plant.
When NOT to Top Off Tomato Plants
In mild climates, indoors or greenhouses, topping is not necessary since the frost and cold temperatures won’t affect them as much. If given the right conditions, indeterminate tomato plants grow as perennials, but productivity decreases each year.
Determinate or ‘Bush’ tomato plants have usually finished their mass fruiting by mid-summer anyway, so there is usually no need to top off these varieties. Some hardy, determinate varieties which fruit early in the season include ‘Cold set’, ‘Earlirouge‘, ‘Subarctic’, ‘Siberia’ and ‘Bush Beefsteak’.
Basic Triggers and Associated Actions for Topping Tomato Plants
Below is a quick guide on the three weather triggers that I use to determine when to top off my tomato plants, keeping in mind that heirloom varieties will need a longer lead time.
- TRIGGER 1: The monthly weather forecast predicts overnight temperatures consistently below 55 °F (13 °C) in one month’s time.
- ACTION: Top the plant to remove any growing tips and flowers from the tomato plant and apply a final dose of high phosphorus fertilizer. Leave all un-ripe fruit on the plant and cross your fingers that they ripen over the next 4 weeks.
- TRIGGER 2: The forecast predicts freezing overnight temperatures in one weeks’ time.
- ACTION: Top the plant again to remove any small green tomatoes and flowers from the plant. Stop applying fertilizer and stop watering. Wrap plastic around the plants each night to keep them warm, or move them undercover.
- TRIGGER 3: The weather forecast predicts a frost during the night.
- ACTION: Either cover it, pull up the whole plant, and hang it in a shed, or harvest the remaining tomatoes to ripen in a shoebox or on the kitchen bench.
Conclusion
There is always the risk of topping your tomato plants too early and depriving yourself of those late-maturing fruits, but keeping an eye on the long-range weather forecast and growing a selection of different tomato varieties can minimize this risk.
