This page is for all those who, like me, want to know a bit more about what makes tomato plants grow.
I’ve also included some advanced tips that aren’t essential for success, but are helpful to maximize the health, growing rate and yield of the plants we are so fond of.
Watering Tomato Plants
It’s very easy to damage the root hairs of seedlings and young plants by over-watering. Roots that are kept wet 24/7 are vulnerable to disease and will not develop to their full potential.
Furthermore, roots need oxygen for respiration (see below) and over-watering reduces the oxygen and air content in soil.
The wet/dry cycle is the best way to water tomato plants which allows air back into the root zone as the soil (or other growing medium) goes from wet to dry.
Soil that is too fine, or contracts greatly as is dries-out and therefore expels air, isn’t suitable for tomato plants.
Acid – Alkaline and pH
This is the way the amount of acid/alkalinity is measured in soil and water, with pH 7.0 being neutral.
Tomato plants like soil and water that is slightly acidic because they are able to absorb the widest range of nutrients (food) when the soil and or water is on the acid side – below pH 7.0.
For tomatoes grown in soil a pH between 6.0 to 6.8 is good.
In hydroponic growing (growing without soil in a medium such as perlite) a pH between 5.5 and 6.5 is good for tomatoes.
Tap Water and pH
The pH of tap water has a significant effect on plants grown in containers of soil (and hydroponic situations too of course!).
It may not be possible to test the multi-purpose compost and grow bags at the garden centre for soil pH, but it is very useful to know what your tap water pH is, and be able to adjust it.
A pH water test kit is inexpensive and can make a big difference when you know the efficiency of your tap water.
My tap water is pH 7.4 which is too alkaline for tomatoes, so I lower the pH to about 6.5.
It’s easy to do this with lemon juice. Just 1ml for every 2 litres takes it down to around 6.4. in my situation, but your tap water and probably lemon juice strength will be different from mine – I use a bottled lemon juice from my local shop.
If you grow tomatoes under cover and water them with tap water, it is best to check that the pH is suitable – needs to be around 6.5.
Rain Water and Pollution
If you grow tomatoes outdoors, rain water is usually around pH 6.5 (or even lower depending on how polluted the air in your region is), so rain water is usually good for tomato plants – if its not too polluted.
My rain water recently tested at pH 6.0 – I live in the West Midlands near Birmingham which shows that rain water becomes more acidic in major industrial areas as it absorbs pollution from the air.
Chlorine and Tap Water
Allow water from the tap to stand overnight in the watering can to reduce the chlorine content.
Feeding Tomato Plants
Over-feeding can be just as damaging as over-watering to tomato plants and is the cause of many problems.
Nutrient build-up can cause toxicity – not so much from the macro nutrients, but the danger is an overdose of the micro nutrients (trace elements) that can cause the greatest damage to a tomato plant.
Too much of one nutrient can also prevent the roots from absorbing other nutrients.
Strength of Nutrients and EC
Nutrient strength is measured in EC, which is electrical conductivity.
A good level for this in tomato plants is between 1.5 and 2.5 depending on the stage of growth and other factors.
On a bright sunny day, plants absorb more water and with it more nutrients. This means that it is more likely that plants may absorb too much food and become over-fed. So, on bright sunny days, nutrient levels – EC levels – can be reduced.
On a cloudy day, there is less intake of water and nutrients, so EC levels can be increased. as there is less chance of over-feeding.
It is not critical on a daily basis when growing tomato plants in soil, but in long periods of sunny or dull weather, nutrient strength (EC) is an important consideration for plants grown in soil.
Tomato plants grow well between 65 and 75C.
Some varieties are happy and grow well at lower temperatures, others excel at higher temperatures.
There is a reasonably wide divergence between varieties in many respects. It is therefore up to the tomato grower to get to know each variety in order to get the best results.
Some varieties have also been developed for specific situations – for wide temperature fluctuations outdoors, or for managed conditions in professional greenhouses.
For tomatoes humidity is best between 55 and 75% – lower or higher than this can cause blossom drop and other setting related problems.
Photosynthesis converts light, carbon dioxide and water into sugars (carbohydrates).
The process of burning sugars to create energy for growth. Oxygen is also used in this process so it is important that there is plenty of air (oxygen) in the root zone.
Water evaporates through the stomata (tiny openings) in the leaves. As water is lost through the leaves, water plus nutrients and oxygen is drawn up from the soil by the roots.
Transpiration increases in bright, warm and windy conditions. A fan near a tomato plant will cause it to transpire more than one at the far end of the greenhouse.
However, if you over-water plants on a cloudy day, when they transpire less and need less water, there is a danger of tomato skins splitting as pressure increases in the plants and fruit.
Substrate and Aeration
Tomato plants can grow in many different media – not just soil.
If the media can hold moisture, air and be free draining roots are happy.
By adding perlite to soil, aeration will be greatly improved and so will the health and yield of plants. Up to 50% perlite for container grown tomatoes is ideal.
Nothing has been mentioned about individual nutrients, growing tomatoes organically and friendly soil bacteria and disease prevention to name just a few more aspects related to tomato growing.
There’s no end to it all!