The weather has been disappointing here in the UK recently, with temperatures lower than usual for this time of the season.

Poor Weather and Tomato Growing

When temperatures are low and condensation and damp air is high, plants are at their most vulnerable to disease.

It’s good to reduce the amount of water plants receive when temperatures are low. Water in the morning to help avoid plants standing in cold wet soil overnight.

Foliar feeding is also best done when air humidity is at its lowest – when air is damp, leaves will not absorb or release as much moisture as when the air is dry.

Keep plants sheltered from the wind and rain – we’ve had plenty of both lately!

When small plants are blown around, plants will become stressed and the fine roots at the base of their stems may be damaged.

Low Light Levels
When light levels are low and/or when air humidity is high, plants require a slightly higher strength feed than when there is plenty of sun and the air is dry – why?

Because of transpiration (see previous newsletters) which is when plant leaves release moisture – the more moisture they release, the more moisture (containing food) is replaced through their roots.

So a plant that transpires a lot, receives more food.

To help balance the nutrient intake, a slightly reduced strength feed is given in good weather, and a slightly increase strength in poor weather.

Cherry tomatoes growing on patio
Tomatoes on patio last season.

Tomato plants are amazing!
If they need more nutrients than they can absorb through their roots, they’ll take them from their lower leaves.

It’s a bit like borrowing from Peter to pay Paul – with Peter at the bottom and Paul at the top – the growing tip always gets the best portions.

Yellow leaves
You can buy the best quality potting compost or grow bags, but unless temperatures are reasonable, both day and night, plants will often display nutrient deficiencies in their lower leaves.

yellow leaves and nutrient deficiency
These yellow leaves around the base of a tomato plant are the result of nutrient deficiency caused by poor temperatures and translocation.

This is because nutrients are only available to plant roots above certain temperatures. So when it’s too cold, the only nutrients that are available to the growing tip(s) are those in the lower leaves.

The lowest leaf branches can be removed. This helps prevent nutrient deficient leaves from becoming infected and passing that infection to the rest of the plant.

Yellow leaves are usually harmless but you may see all sorts of marks and many shapes and colours appear on lower leaves at this time of the season.

The best way to proceed is to remove the affected leaf branches and to foliar spray the plant with a “pick-me-up” such as:

  • Liquid seaweed extract – contains a good range of nutrients.
  • A general feed like Miracle Grow that contains micro nutrients.
  • Magnesium – will help make light green leaves a darker green.
  • Calcium nitrate contains nitrogen and calcium for strong healthy growth – also good for avoiding blossom end rot.

All of the above are best given as a foliar feed in order to avoid creating an unbalance in the soil.

Liquid Seaweed
Liquid Seaweed

You will also find more information and tips for this time of the season in last year’s newsletters. I try to be topical, so read the ones around this time last season.

I think we have some better weather on the horizon starting next week – hopefully!