Growing San Marzano Tomatoes in Kratky Hydroponics – Update: Week 6

I just realised that I forgot to write a post for last week, oops. Sorry about that. Guess the jump of growth between the last post and this one is going to be significant. This post is going to be big (not just plant growth), but because I discuss edema, flowers and fruiting too.

Lets look back at week 4 growth:

San Marzano Tomato 1 Month, In Kratky Hydroponics
San Marzano Tomato 1 Month, In Kratky Hydroponics

I was so proud of how big they were growing… and how fast – each day seemed to produce another branch, another leaf, or another inch or two of height… little did I know that the plants would keep growing at such a speed, even two weeks later. I have created a monster; a gorgeous, hopefully soon to eat yummy, monster:

San Marzano Tomato 6 Weeks Old, Grown In Kratky Hydroponics
San Marzano Tomato 6 Weeks Old, Grown In Kratky Hydroponics

Its getting huge! We have two of the trellis supports already installed, and tonight I will be putting in the third. Thats a trellis each week…

The Curious Case of Edema

Would you believe that I have actually been cutting branches off? We’ve actually been having a problem with how fast this plant is growing. So fast that it’s actually becoming a serious problem and risk, for the plant itself.

Edema on San Marzano Tomato Plant Leaves
Edema on San Marzano Tomato Plant Leaves

See those little green spots on the tomato leaves? That’s edema. Its what happens when the plant is absorbing too much liquid… Is that even possible in a hydroponic system? Yeah it is. Edema causes the cellular structure on the leaves to swell up as they absorb moere and more liquid, to the point that they will rupture, often killing that leaf. Often you will also see crusty spots on the leaves from dried sap and water.

In mild cases its not usually an issue, but more and more of our tomato branches were becoming effected. It tends to effect the lower branches or leaves first, slowly effecting more of the plant if the environment remains unchanged.

There are a couple reasons why it can happen:

  • There isn’t enough airflow around the plant and the plant isn’t transpiring enough (sort of like you getting hot and sweaty without a cool wind). This can also happen if the plant leaves is too dense and thick, restricting airflow around inner branches. This is the most common reason.
  • The nutrients are unbalanced; the plant is sucking up too much liquid to try and get enough of one or more nutrients.
  • The water is too warm whilst the leaves are cooler, causing the plant to activate drinking mode. Sort of like when a plant is growing in a hot region – when it rains the upper plant becomes cool and signals to the roots that fresh water is being supplied.

I will write a blog post covering edema bit more and ways to resolve this. It affects all plants, not just tomatoes.

In our situation, the foliage was becoming too dense. The constant but small airflow that we had in the room wasn’t reaching the inner branches and leaves, so the plant wasn’t able to lose the excess liquids through sweating.

Over Dense Foliage on San Marzano Tomato, Week 6 Growth in Kratky Hydroponics
Over Dense Foliage on San Marzano Tomato, Week 6 Growth in Kratky Hydroponics

For now our solution was to maintain a slightly more average temperature in the grow room rather than cooler at night and warmer during the day. We are still researching the ideal fan for our grow room as some people have had issues with the common oscillating fans causing leaf burn due to overexposure of wind.

Fruitful Endeavours

Flowers on San Marzano Tomatoes at 6 Weeks, Grown In Kratky Hydroponics
Flowers on San Marzano Tomatoes at 6 Weeks, Grown In Kratky Hydroponics

It’s not all bad news; our “hard work” is paying off. The tomato plant is only 6 weeks old, and yet we have been getting flowers now for nearly two weeks!

Flowers on San Marzano Tomatoes at 6 Weeks, Grown In Kratky Hydroponics
Flowers on San Marzano Tomatoes at 6 Weeks, Grown In Kratky Hydroponics

San Marzano are an indeterminate tomato plant variety, meaning they will continuous flower, fruit and grow indefinitely as long as the environment is ideal. So it makes sense that not all the flowers are opening at once. I did a count of the flower buds that I could see – both opened and unopened. There was over 35 flower buds!

Flowers on San Marzano Tomatoes at 6 Weeks, Grown In Kratky Hydroponics
Flowers on San Marzano Tomatoes at 6 Weeks, Grown In Kratky Hydroponics

The average San Marzano tomato weighs around 120-140grams (4.2-5oz). Assuming all 35 flowers produce tomatoes, thats a minimum of 4.2kg (9.2lbs) of tomatoes! I’m so glad that I have bought some canning equipment so I can bottle up these delicious tomatoes.

Have you preserved your home-grown or store bought tomatoes? Whats your favourite way to use tomatoes? Mine is definitely pizza sauce. Let me know in the comments below.