How to Manage Moisture in Container Tomatoes: Fruit Cracking/Blossom End Rot

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Part One of Two:

The key to growing large bountiful tomatoes in containers is moisture control. Moisture control is the goal with control being the operative word. Tomatoes and most vegetables need even moisture. Periods of prolonged drought followed by too much water damages plant systems. I am going to focus on the tomato plant and how moisture control impacts the growth of the container plant.

A container tomato needs continued, mostly even, moisture. A single day of a fully dried out container, which can happen in a day when your tomato plant is a good size and the day time temperatures are in the 80’s, will harm your tomato. At face value, drought will limit growth. The plant will pull moisture from the tomatoes to survive. Fruit production will be limited and plant and fruit size will be smaller than designed. Many other things can happen with your tomato plant when moisture is uneven. Uneven means totally dried out, then soaked, mostly dried out, soaked again and another day of drying out completely. This is the bane of growing tomatoes in containers.

A dry container tomato followed by an excess of water can crack your tomatoes. You have seen cracked tomatoes before. This comes from a plant that is struggling with uneven moisture. They gorge themselves on the excess water, swell quickly and crack. The other problem has to do with a combination of factors but uneven moisture plays a huge role. Blossom end rot is the browning of the bottom of the tomato where the blossom was once attached.

Blossom end rot is physiological disease. It is not spread by a virus or fungus. It has to do with moisture, root systems and the ability of the plant to use calcium. It is most prevalent during vigorous tomato development but can occur at any time while the plant develops fruits. If a plant is struggling to absorb water, it cannot transport minerals properly throughout its system. A lack of calcium in the soil or the lack of the plants ability to transport and use calcium will cause blossom end rot. There are 2 ways to address this: correct moisture control and the addition of calcium (lime). Most container soils have sufficient nutrients in them and the main cause of fruit cracking and blossom end rot is due to moisture control.

The best way to manage your container tomatoes so that they grow large and stay healthy is a plan to address moisture management from the beginning. Seriously, tomatoes start out small and visually we assume an under sized container can handle them. You have to imagine how a 5-6 foot tomato will look in the container. At minimum you will need a container that holds up to 5 gallons of soil mix. I recommend using paint containers from your local do-it-yourself stores.

I have a basic design that works. It is a semi-self watering container system that will buy you the extra umpf for maintaining even moisture control. Unless you can water daily and sometimes twice daily on every hot day, you want some sort of self watering system to help you out. The supplies required for this are: 2 five gallon paint containers, a bag of moisture control garden soil, a funnel, a drill with a ¼ drill bit and an old bathroom towel.

Part Two: Coming This Week.