Canary Plants and Feeding Tomatoes

Having reached the second half of June, the rest of the season is mainly concerned with:

  • Feeding
  • Watering
  • Pruning
  • Problems

Many problems can be avoided if we get the first three right!

Plants often tell us what they need – the answer isn’t blowing in the wind, or even in the tea leaves – it’s displayed in the plant leaves!

Canary Plants and Feeding
However, it can take a week or more for problems to show in the leaves of a tomato plant, and by then, the plant’s growth has been effected. Some growers use a “canary plant” (not a real plant) similar to the canaries used by miners, working down the mines!

For example, a cucumber plant will display some nutrient deficiencies much sooner than a tomato plant. By growing a cucumber plant alongside our tomato plants, we can get advance notice when a nutrient deficiency is likely to occur.

Feeding tomatoes is a funny business and some actions have the opposite effect …

Overfeeding can cause nutrient deficiency and Blossom End Rot – a shortage of calcium.

The reasons are because, some nutrients, if given in too high a concentration, will block other nutrients from being absorbed by a plant’s roots.

Foliar feeding avoids this problem and is most effective when a top-up of a nutrient like magnesium or calcium is needed.

Tip: Keep soil feed to just the basic tomato food and add other supplements by foliar feeding.


How To Foliar Feed
When foliar feeding, it’s best to spray the underside of the leaves – that’s where the leaf holes are (stomata) and a quick way to get a nutrient into a plant’s system.

It’s also good not to spray the whole plant – why? – because when every leaf of a plant is wet, a plant stops absorbing moisture and nutrients through its roots.

This temporary interruption can cause Blossom End Rot, but by spraying just some of the leaves, a plant is still able to release water vapour from its other (dry) leaves and continue its uptake of calcium. Even a slight interruption can cause Blossom End Rot.

Tip: When spraying calcium, spray only the leaves above and below each truss – the leaves nearest the fruit.

When spraying magnesium, spray only the top or bottom leaves.

Watering and Feeding
The great thing about reservoir systems such as the Quadgrow Planter and watering valves like the Aquavalve, is that they provide water and nutrients as plants need them. In other words, there is no interruption to the uptake of moisture and nutrients. This is a huge advantage when it comes to growing tomatoes.

Leaf Problems

Magnesium deficiency on lower leaves.
Magnesium deficiency on lower leaves and very common – not a problem!

Looking at the broad picture, it’s easy to get hung-up on every little speck and spot and all those disease pictures on the internet!

If the problem is limited to the lower leaves, its probably caused by a nutrient deficiency such as magnesium or a minor disease that can be controlled if the effected leaf branches are removed.

Problems on upper leaves are usually more serious and difficult to deal with.

The Limiting Factor
For the best growth, the challenge is knowing what a plant needs most – its “limiting factor”.

All other things being equal, the limiting factor is what is holding the growth of a plant back – stopping it from its full growth potential.

If there is plenty of everything except sunlight – a plant’s limiting factor is getting enough sun.

There’s not a lot we can do about that one, but there is a lot we can do about watering, feeding, disease prevention and pruning, all of which can improve the rate of growth and the quality of the taste and appearance of the fruit.

Over the next few weeks we’ll look at some options for feeding, the best way to prune without reducing the flavour of the fruit and one or two unusual ways to help prevent disease.

I hope your plants are doing well!



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