- You’re now watering a tomato plant (a tiny one but still…) and you should consider it to be like any other plant in your collection. You water it until water pours out the bottom of the pot. And you finger-check it to ensure it’s dry enough to water.
- You feed every week without fail.
- I no longer worry about warm water. Room temperature water is fine for transplants that are growing well.
- It’s really that simple.
A Pro Technique For Temperature Of Growing Transplants
- Optimum daytime temperature for tomatoes is 72-74 for a young plant. (note there is a difference between growing and fruiting temperatures covered later)
- Optimum night temperatures 62-64 F. for a resting young plant
This is something they do not teach you in gardening class but is something I read about back in 1991 when I was still running my nursery.
DIF is the difference between day and night temperatures.
So a Positive DIF is when the day temperature is higher than the night temperature (written as +DIF)
Zero DIF – when they’re the same
Negative DIF when the daytime is lower than the night temperature. (written as -DIF)
It’s counterintuitive but Negative Dif (when night temperatures are higher than day temperatures) will create a shorter, stockier plant with more branches.
And tomatoes are in the high response class which means they will stay much shorter, stockier when the night temperatures are higher than the day temperatures.
So yes, you raise the thermostat at night and turn it down in the morning.
The range of DIF is from 1-15 degrees F. In other words, the tomato plant will give you the shortest stockiest growth if you create a 15F degree difference between the night and day temperatures (warmer by 15F at night than during the day)
Research further showed this difference was “primarily” felt if the DIF was applied between “just at sunrise” for a few hours. It didn’t have to be all day.
I would go out in the early 5am morning just as the sun was starting to come up to open up the vents and blast our greenhouses with cold air. By the time the sun warmed the greenhouses up, the main effects of DIF were finished for the day. So our plants received a night of warm air, were blasted by cold air to make a 15F difference for as long as the fans could hold the sunshine heat rise at bay. As the sun set, the greenhouses would be cooled again until it was down and then the fans would be shut down until the next morning. The furnaces would kick back in, the temperatures would rise and our plants had a negative DIF.
And they stayed short – very short and blocky – and no other greenhouse in the area seemed to be doing this. 🙂
In your home growing area – you can use a small heater to mimic the same effect.
Some more reading on DIF
The Question You May Be Asking
How do we make DIF work with the preferred tomato growing temperatures?
That answer is to apply DIF only in the early morning hours – cool to 64F from sunrise for three hours and then allow the temperature to rise to 72F.
How Do We Do That In The House?
Ah, the eternal problem of balancing growing a plant inside a house where you’re trying to live too. 🙂
We have a small basement room where I can close the door and adjust the heat independently.
Or. I often don’t worry about it because I know that even if I screw up and produce a tall seedling, I can recover when I plant. And that lesson is coming up.
In summary, if I have to choose between a healthy but too-tall transplant or messing about too much with heat and cooling and DIF calculations, I now take the too-tall plant. I can fix that easily (in the next section).