We all know that tomato plants need to be kept warm to grow successfully and that they like lots of light.
However, keeping them at an ideal temperature is next to impossible unless you have a professional set-up – so let’s talk about some realities!
- Germination is best around 21C.
- Keep seedlings and young plants around 18C (if possible!).
- Outside – above 15C and best not below 10C at night – difficult to achieve if growing outdoors!
- When tomato plants reach around 35C they stop growing and the same is true when temperatures are much below 10C depending on the variety.
- Humidity combined with low temperatures also has an influence on growth where condensation is high – see transpiration.
Germination will take about five days if the temperature is kept at 21C but if temperatures vary widely, it will usually take longer.
Seedlings are grown in the spring (of course!) but the problem for many regions is that light levels are low and days are short in spring-time.
Temperatures kept too high
This means that if temperatures are kept artificially high with low light, seedlings will become leggy.
Temperatures too low
If temperatures drop too low and seedlings are sat in cold, water soaked soil, “damping off” where they wither and die!, is a possibility along with poor growth and fungal disease.
I’m painting such a gloomy picture – again!
How to cope with high’s and low’s
If temps are too high or too low it is best to under water rather than over water seedlings. This will help stop them from becoming leggy and reduce the risk of disease.
I once left two young plants out on the patio at night and the temperatures dropped below freezing! Fortunately the plants, an Alicante and Moneymaker completely recovered and produced one of the best harvests I’ve ever had from these varieties.
Healthy plants can cope with adverse conditions – on the odd occasion, but I would never try this on purpose!
Also, it was a dry night so the plants didn’t have to cope with wet leaves – the combination of cold temperatures and wet leaves are the worse possible conditions for tomato plants.