Container Gardening

When I went to my mother’s house yesterday, I found her (in-ground) tomatoes suffering from a fairly severe case of early blight.  In my part of the world (Massachusetts), this has been an extremely wet June, leading to some delays in vegetable growth and some fun and exciting health problems for our plants.  Inspired, I’ve decided to talk about early blight in container tomatoes.

As with most vegetable diseases, this is more common with in-ground plants than it is with vegetables grown in pots.  Most plant diseases incubate in the soil, and the soil for in-ground vegetable gardens is more likely to be contaminated than the soil in containers, especially if you use fresh potting mix every year for your container garden.

However, the fact that it’s more common with in-ground tomatoes doesn’t mean you don’t see it when growing containers in pots.  So, what is early blight?

Early blight is a fungal infection that can affect eggplant, pepper, potato, and tomato plants.  It tends to do the most damage to potato and tomato plants.  It survives between hosts in the soil, living off the plant matter in the dirt.

Early blight can affect the leaves, the stem, and the fruit of tomato plants.  The symptoms vary depending on what part of the plant you are looking at.

Leaf Lesions

The first place you usually spot early blight is on the oldest leaves, near the bottom of the plant.  It will show as brown blotchy spots, surrounded by a yellow halo.  Eventually, the yellow will overtake the entire leaf, and it will wither and die.

If the damage spreads to the stem, it will show as dark, elongated patches on the stem.  Fruit can also be affected, with dark sunken lesions on the fruit.  These are leathery to the touch, and usually occur at the stem end of the fruit.

If you catch early blight when it first appears, it is usually correctable.  Early blight spreads up the plant from the lowest affected leaves, so when you see leaves with the characteristic lesions, remove them immediately.  Damaged stems will eventually kill off any plant growing beyond them, so if you have main stem damage, it is best to pull the entire plant and start over.  Any affected fruits should be picked and thrown away, letting the plant focus its energy on healthy tomatoes.

You can use a mild fungicide to catch early cases of blight.  Organic gardeners find that a milk spray (one part milk to 10 parts water, misted on the plant after every rain), helps prevent fungal infections or treat existing ones.

Preventing blight is usually easier than fixing it, however.  The most common way for tomatoes to develop blight is from infected soil splashing up onto their lower leaves.  To prevent this, make sure to tie up all leaves that hang close to the ground.  You can trim the lower branches entirely as the plant grows: these won’t get as much sun and will not thrive anyway.

You can also mulch over your soil, creating a barrier between the dirt and the plant.  This has the added benefit of keeping the soil more moist between watering sessions, which is always a challenge for container gardeners.

So, you’ve decided to try growing tomatoes in containers.  You’ve chosen your containers, planted your tomatoes and watched them grow.  Everything has been going great!

Then, one morning, you go out to check on them, and something isn’t right.  Maybe the leaves are off-color.  Maybe the fruit looks wrong.  One way or another, your tomato has gotten sick.  What do you do?  Here are three common problems with potted tomato plants that affect the fruit and how to prevent or deal with them.

1. Blossom-end rot

Blossom-end rot is exactly what it sounds like: the tomato begins to rot from the place where the blossom attached.  It is caused by low levels of calcium in the plant.  An ounce of prevention is worth a pound of cure here.  The best way to keep blossom-end rot away from your plants is to keep calcium levels high.

You can start your plants off well by crushing some eggshells in the soil before planting your seedlings.  Fertilize with a non-ammoniacal nitrogen fertilizer, and make sure you are watering regularly and your pots have good drainage.  DO NOT OVER-FERTILIZE.

If you already have blossom-end rot, try to stabilize your plant’s moisture as much as possible.  It’s a good idea to pick and throw out affected fruit as soon as you notice to reduce strain on the plant.

2. Sunscald

If your underripe tomatoes are getting hard, white or light-colored patches on them, they may have sunscald.  These patches will eventually blister and sink in.

Sunscald is caused by too much direct sunlight on the fruit.  Tomatoes are very leafy plants, and those leaves serve two purposes: they soak up a lot of light for energy, and they shade the more delicate fruit.

To prevent sunscald, try to keep your tomato plants lush and thick.  If you prune them, make sure all your fruits remain shaded when you are finished.  If something else causes your plant to lose leaves, you can protect your fruit with light screens.

3. Growth Cracks

When a tomato grows too fast, the skin can’t always keep up.  When this happens, you see cracking.  There are three kinds of growth cracks.

• Radial cracks: These cracks start at the stem of the tomato and reach outward.
• Concentric cracks: These cracks make circles around the stem, never touching it.
• Russeting: In russeting, tiny cracks form and scar all over the tomato, giving the fruit a rough appearance.

Growth cracks almost always result from a dry period followed by a very wet period, where the tomatoes work to make up growth.  To avoid cracking, make sure your tomatoes have a consistent, steady water supply.  Regular fertilization will also help.

Note: If your pots are too small, they may have a hard time holding enough water.  Consider moving to larger pots if cracking is a regular problem in your container tomatoes.