Everything is related to transpiration
It is by transpiration that the nutrients pumped by the roots are able to climb up to the head and the fruits. Anything (ANYTHING) that stops transpiration is compromising health and growth. The nutrients can’t reach the top of the plant anymore.
We start to see deficiencies (yellow leaves), blossom-end rot, and tiny, weak stems.
Extreme temperatures are a dangerous threat that stops transpiration. But we want to focus on humidity.
The goal is to ensure a good transpiration rate throughout the day.
When air moisture is too high, the plant doesn’t have enough room to breathe out its water. That is when problems arise. Growth stops, leaves and fruits aren’t fed anymore, AND fungal diseases develop.
Keeping control over humidity: over-irrigation
The easiest way to avoid having too much moisture is to not add more moisture to the air. Over-irrigating does just that.
How do you know if you are irrigating too much?
- When you put your fingers in the ground at different times of the day, is it always wet?
- Is the top of the soil always dark, with some green algae starting to grow?
If the answer is yes, reduce your irrigation by 20%. That's 2 minutes on a 10-minute irrigation.
Last irrigation
Another thing to keep in mind is not to spend the whole night with wet soil.
If, in the morning before the first irrigation of the day, your soil is wet at a finger’s depth, try to give your last irrigation sooner in the afternoon. Don’t irrigate AT LEAST 4 hours before sunset.
Irrigation depends on cloud cover
The amount of water the plant needs is directly correlated to the amount of light it receives. So, when it’s cloudy, you have to irrigate much less than on a sunny day.
For example, if you give 60 min on a sunny day, you should give:
- 40 min on a partly cloudy day
- 20 min on a fully cloudy day.
This will help you avoid adding too much moisture to the air. This gives you a better chance of keeping the right humidity. It will also prevent flushing your minerals.
Maturity of the plant
If you give 60 min to mature plants, you should give less time to smaller plants.
A beef tomato plant is mature when it reaches 18 leaves. The amount of water to give to beef tomatoes that have fewer leaves is a simple rule of three.
- 60 min x number of leaves/18 leaves = minutes of irrigation
So, for a 9-leaf plant, this would be the equation:
- 60 min x 9 leaves /18 leaves = 30 minutes
Spacing
We discussed optimal spacing in this ebook, but here we would like to give a simple rule of thumb:
You should be able to see through a double bed of trellised crops.
If you can't see someone working in front of you on the other side of the bed, you need to prune!
Number of leaves required per crop:
- Beef tomatoes, 18 leaves.
- Cherry tomatoes, 14 leaves.
- Cucumbers, 20 leaves.
Try to stay close to these numbers.
If you have enough leaves and can't see through, the spacing is too crowded. Top off some plants. Then, harvest the ripe fruits and cut off the plants.
Airflow
Having good airflow is mandatory. The more height you have on your roll-up's side, the better.
Insect netting is a great way to keep off pests. But it is also a huge airflow reducer. If you don't need it, removing it will help a lot.
Horizontal air flow fans (HAF) are a great way to keep air circulating 24/7. We recommend having at least 4 fans for a 30’x100’ greenhouse.
Dehumidification Pulse
One way to dehumidify and stop fungal growth is to pulse the air out in the morning.
You do this by opening your roll-ups, starting every fan you have, and starting your heater for 20 min.
This will let in drier air and keep your temperature close to its current level. Thus, reducing your tunnel's absolute humidity.
We aim for 20 min as a guideline. But the real duration depends on how long it takes to return to a disease-risk-free zone of 3g/m3 of humidity deficit.
Want to learn more about humidity deficit, click here.
That's it: a few tips to keep good humidity
It will ensure constant growth and fruit quality!
Keep in mind that humidity is not only disease-related but a key element in plant growth and big yields!
Want to automate your humidity control, and profit from a low disease greenhouse? Check out our solutions!