It’s the first day of the best month for sowing tomato seeds.
The sun is shining in my part of the world and the urge to sow a few seeds this weekend is overwhelming!
If you have more willpower than I do, the best sowing time for tomatoes is from the middle of March to the beginning of April in the UK.
I usually start by sowing varieties that won’t become too leggy in low light. Getting seedlings through March and April in dull, short days is a challenge – always kept indoors overnight of course.
Also, I like to sow bush varieties first – they won’t grow as tall as indeterminate plants so are easier to manage before planting out in their final position.
This hormone (or group of hormones) causes the internode of a stem (distance between sets of leaves) to elongate and cell division to occur. Gibberellin is made in the stems, roots and young leaves.
Elongation of the internodes is a characteristic in tomato plants that isn’t helpful because it can reduce the number of trusses on a tall variety before it reaches the greenhouse roof!
Leggy Seedlings and Young Plants
If a plant doesn’t receive enough light, it will also grow tall and leggy with greater distance between leaf sets (internodes) than normal. In this case, the hormone plays it’s role to help the plant search for light above.
Too much nitrogen is also a cause of leggy plants in the early stages of growth – especially when:
- Light levels are low
- Temperatures are moderate
- Moisture in the soil is high
To keep plants from becoming leggy in low light conditions, reduce temperature and especially moisture in the growing medium.
Gibberellins are often used on commercially grown dessert grapes so that the stems attached to the grapes are longer and give more room for the grapes to grow, causing them to be bigger.
The variety Shirley has short internodes as one of its natural characteristics and is therefore one of its advantages.
Anti-gibberellins are used to prevent commercial crops such as bedding plants grown in glasshouses from becoming leggy. Hormones that are used to manipulate plant growth are called Plant Growth Regulators – PGR’s.
Transpiration – Tomato Plants Perspire!
As water vapour is lost from the leaves, water is replaced through the roots.
Without this loss and replacement process, plants wouldn’t be able to absorb the nutrients they need, that are dissolved in water, and taken up through their roots.
If a plant loses moisture from its leaves faster than it can absorb moisture through its roots, the plant wilts.
If a plant absorbs moisture from its roots faster than the leaves can perspire (transpire), fruit will crack and sometimes leaves will appear bubbly/spongy as the pressure inside increases. This often happens when soil that has been allowed to become dry gets a good watering or a heavy downpour of rain!
Moisture loss and availability
If I were a tomato plant, I would probably spend a lot of my time worrying about the amount of moisture loss from my leaves and the amount of moisture available around my roots!
Keeping the right amount of moisture, or pressure, in a tomato plant is a full-time job. Get it wrong and the plant wilts or the fruit cracks or it doesn’t get enough food and that’s just for starters!
So why do we need to know this stuff … is it important for my plants?
Putting into practice
Understanding how transpiration works helps us to get the most from the circumstances in which a plant is growing. Or even change those circumstances!
Here are four conditions that effect the amount a plant transpires.
Transpiration increases as:
- Light increases
- Air flow increases
- Temperature goes up
- Air becomes more dry (less humid)
Have you noticed that when you put young plants outside for the first few times in the spring, they are more likely to wilt in the cooler conditions on the patio, than in the warmer temperatures on the windowsill!
The reason is because there is more air movement outside in the garden, so water loss increases from leaves. They may also suffer stress from the change of conditions.
One of the problems is, when plants are still young, they don’t have the root area to absorb moisture quickly enough so they may wilt in direct sunlight.
Transpiration and mineral take up
Reducing the strength of nutrient levels helps too.
Over-feeding plants on a sunny day may also cause them to wilt because higher levels of minerals in the root area, reduces the rate of water a plant can absorb because of osmosis. We’ll look at osmosis next week.
Of course the more leaves a plant has, the more water it will lose when the sun comes out and the breeze blows. A good reason for de-leafing and removing lower leaves in mature plants.
Temperature and humidity play their part too
As you might imagine, plants lose more moisture in warmer conditions. Dry air will also increase vapour loss from leaves than when it’s humid and the air is already full of moisture.
A greenhouse that isn’t well aerated and contains a lot of condensation will reduce transpiration greatly and growth will be reduced.
Also, foliar spraying in humid conditions is much less effective and is likely to increase the chance of disease.
Understanding transpiration helps us to grow plants better.
I hope the sun is shining where you are.
The most economical way, if you grow around 30 or more plants, is probably a seed tray filled with compost. A lid is also useful to retain humidity when the seedlings germinate. The humidity inside the lid helps the seedlings discard their seed husks and helps prevent stress as the seedlings acclimatise.
Another inexpensive method, if you only need a few plants, is to use a grow pot/kit which you will find in a discount store. It includes seeds and a small amount of compost – just sow in the pot and that’s it!
Jiffy pellets are also a very good way to germinate seeds and you can buy these included with a propagator. The windowsill type is very popular and useful.
It’s fun to watch the jiffy pellets expand in a tray of water!
However, the ultimate way to germinate seeds and grow seedlings is by using Root-it sponges. These come in trays and also in a standard or windowsill propagator.
The advantage sponges have over other methods is the air and moisture ratio which helps develop a very good root system quickly.
Also, like jiffy pellets, there is no need for the roots to be disturbed when transplanting. There is also no need to buy bags of seed compost if sowing into pellets and sponges.
However, you can obtain good results whatever method you use.