Tomatoes and Extreme Weather

I usually put the final touches to the newsletter early on Saturday morning – just before the email goes out. It gives me the opportunity to be topical and talk about the weather!

Tomato plants growing outside will probably have received a lot of rain overnight if you are in the UK – and there’s more to come.

It’s good that temperatures are reduced when it rains but the problem rain can bring is saturated soil.

What happens when oxygen is removed from soil?

• Growth is reduced – respiration slows owing to lack of oxygen in the root zone.
• Nutrients are unable to be absorbed – without oxygen in the soil, plants are unable to absorb many of the nutrients they need. You often see tomato plants that have been over watered with pale yellow leaves because they can’t take up the nutrients they need from the soil – even though the nutrients are there!
• Root disease sets in very quickly if soil remains saturated for more than a day or two.

There isn’t a lot you can do to avoid the rain, but it’s best not to sit pots in trays in very wet weather. Also, give pots and containers every opportunity to drain.

If tomatoes could talk, they would say … “It ain’t half hot Mum!”

The weather (before today) has been very hot and it’s been an excellent season in the UK so far. However, high temperatures have posed a challenge for many readers of the newsletter who have reported problems including:

• Blossom End Rot (BER) – even on the cherry varieties!
• Tomatoes with a disappointing taste – after all that effort!

Blossom End Rot
BER is one of those problems that even the most experienced grower will find on one or two of his/her tomatoes.
Some varieties are more susceptible than others and some growing methods are more prone to BER than others.
Although the cause of BER is calcium deficiency in the fleshy wall as the fruit is swelling, the source of the problem is an interruption to the plant’s water circulation – a bit like turning off your central heating system. As soon as the plant runs low on water, even for a short time, the calcium supply to the swelling fruit is interrupted and the result is BER!

Providing a watering system that can cope with hot weather is the key – manual watering morning and evening may not be enough.

Tomato Taste
To put all the effort into growing your own tomatoes and end up with fruit that tastes little better than the supermarket tomatoes is disappointing to say the least!

Unfortunately, there are so many variables involved, especially if growing organically. For example, it is almost impossible to measure the amount of nutrients plants are receiving and nutrient strength has a direct effect on the taste of tomatoes.

Tomatoes won’t taste exactly the same every season because of the variables involved, not to mention the weather. However, there are ways to avoid tasteless tomatoes so here are a few tips.

Plants run out of energy
The hotter it is, the more energy (sugars from the leaves) a plant uses to keep itself functioning (respiration).

The problem is, in very hot weather, especially in a greenhouse, plants can use more energy than they make. When this happens it is very important to find every way possible to keep them cooler, otherwise the sugars that should be sweetening the fruit are being used up by the plant because of the hot temperatures.

Reflect sunlight – don’t absorb it
Direct sunlight on black surfaces – especially plant pots and containers is damaging to roots and will over-heat a plant causing stress and sugar-free tomatoes (that’s sugar-free in a bad sense!).

Use white paper, card or plastic on the front of black pots … and shade black trays that pots are stood in too. Also, Quadgrow Planters have black reservoirs, so shade them or stick white plastic etc. on the front.

Just put your hand on any black surface in direct sunlight and feel what the plants have to cope with!

Black surfaces also give off heat – it’s like having extra heating in the greenhouse – I think I’ve made my point!

Another tip for improving taste is deleafing
Removing ageing leaf branches up to the first truss is good, but remember that trusses of tomatoes receive their sugars etc. from their nearest leaf branch. Removal of leaf branches above the first truss is best done after the fruit have started to ripen. Otherwise, there may not be enough sugars from the leaves to go ’round.

I mentioned earlier that a higher nutrient strength increases the taste of tomatoes. One reason for this is because it reduces the water content of the fruit.

Feeding tomatoes
There are many differing views about feeding tomatoes. One reason is because plants go through different phases of growth – each one requiring a different strength/balance of nutrients for optimum results.

Giving different strengths of food throughout the life cycle of a tomato plant isn’t essential, but it is one area that directly affects taste. Next season I’ll make a number of feeding plans available, from simple (with a few tweeks) to more advanced for the tomato grower who has more time!

Tomatoes and acidity
You will find that at the beginning of the summer, tomatoes contain a slightly higher acid content than in mid-summer. So the toms picked from your plants should become slightly less acidic as the season continues.

It’s still raining outside – I had better pop out into the garden and check on my plants!

Regards,
Nick