If there is a cold snap around the corner, you and your garden should be prepared. In order to be, you need to know, which temperatures are dangerous for your tomato plants and what to do in order to save your delicate plants. So how much cold can tomatoes tolerate? A quick guide!
What to keep in mind
Keep in mind that temperature is a complex thing! To just have a look at a thermometer is not always reliable as there are several factors to keep in mind.
Wet plants are more prone to suffer damage from the cold than dry ones. Cold winds are also increasing the risk as they cool the surface of the plant directly. Those factors can result in plant damage, even though a regular thermometer might not show a temperature quite low enough for you to expect this.
The physical state of a plant of course also determine, how much cold tomatoes can tolerate. Weak, sick or very young plants are naturally more susceptive to damage of all kind, as the cellular structure can be compromised already. Additionally it is important to be gentle when moving plants – for example when they are moved outside after being seeded indoors.
They can suffer from too much of a temperature difference or too much of either sun or shade. To avoid this kind of damage it is good to harden them off patiently.
The perfect temperatures for tomato plants
To thrive tomatoes need temperatures higher than 18 Celsius / 65 Fahrenheit. Night time temperatures should not be lower than 10 Celsius / 50 Fahrenheit to ensure healthy growth and a good fruit set.
Temperatures below freezing
Temperatures below freezing do lead to frost damage on the plant. If it freezes just for a couple of hours, cell destruction could be reduced to only a part of the tomato (like tender, outer leaves and flowers). From this kind of shock a healthy plant can normally recover. Otherwise the whole plant will be killed.
Temperatures below 5 Celsius / 41 Fahrenheit
Low temperatures close to freezing lead to a complete stop in plant and root growth. The metabolism of the plant comes to a hold which slowly starts damaging the cells. The plant will suffer permanent damage after 5 to 7 days of constantly low temperatures. A short cold spur will lead to droopy leaves but the plant will recover with temperatures warming up.
Temperatures below 10 Celsius / 50 Fahrenheit
The plants cellular functions are slowing down significantly. This will lead to permanent plant damage after around 2 weeks. In low temperatures like this pollination is highly unlikely which means that no fruit will grow. existing fruit will stunt in growth and is susceptible to disease.
Even with only night time temperatures this low, the plant will suffer nutrient deficiency after a couple of weeks. This is due to the roots struggling to absorb several vital components.
Temperatures below 15 Celsius / 59 Fahrenheit
The plant will grow slowly but it is almost sure that pollination will not be successful. Additional to this, the root system struggles to take up nutrients like iron, calcium and phosphorus. In consequence the leaves will start to show damage after around 2 weeks of constantly low temperature as well the existing fruit (discoloration, blossom end rot, etcetera). Damage in the fruit is irreversible. The damage in the leaves what who ever can be reversed with temperatures warming up again.