At its simplest, osmosis is the movement of water into plant roots.

More specifically, It is the movement of water/nutrients from a weak solution (outside the roots) to a stronger solution (inside the roots). Roots contain a strong solution of sugars etc. so they can absorb a weaker solution of water and nutrients from outside in the soil.

Nutrient Strength
What happens if the solution outside the roots is the same or stronger than the solution inside the roots?

Or in other words … what happens if I give my tomato plants a very high concentration of tomato food?

Instead of the movement of water and nutrients into the roots, it will have the opposite effect and water and nutrients will be drawn out of the roots and the plant will wilt.

Speed of Movement
This is where the subject of osmosis becomes very relevant to tomato growing.
A weak solution (just water) will move more quickly into the roots than a slightly stronger solution.

In other words, a plant can absorb food at half strength faster than it can absorb food at the full recommended strength.

So how might we use this knowledge?

On a hot day when plants need plenty of water, feeding them at full strength will slow their water intake. It may even cause them to wilt.

The problem with soil
We just don’t know what’s in it! Furthermore, there is a tendency for nutrient salts to build up in containers of soil and grow bags and become stronger than we are aware of.

This leads to all sorts of issues including:

Stress, damaged roots, undersized ripe fruit, low yield, nutrient deficiency and toxicity etc.

A good flush through with tepid clean water can be helpful half way through the season to remove any nutrient salt build up. Think of it as a “detox” for tomato plants!

Growth can be managed on a more technical level by using various nutrient strengths and the process of osmosis.

More about this in coming newsletters!

These issues are more relevant to those who use standard tomato feeds such as Tomorite than to those who use organic methods. Standard tomato food contains higher levels of nutrient salts than organic feed (usually).