Tomato Plant Care: Take Steps for Disease-Free Tomatoes

Offer Tomatoes Support

Almost all tomatoes need some form of support. Left to their own devices, vining, or indeterminate tomatoes, would sprawl along the ground, but we want to grow them vertically to make the most of space and minimize transmission of soil-borne diseases such as, for example, septoria leaf spot.

• There are different types tomato supports that can be used throughout the garden: sturdy canes for outdoor plants and string supports for greenhouse tomatoes. (See video for a demonstration on both tying a stem into the cane and weaving a string support around a stem.) Weaving stems into position are best done in the afternoon/early evening, when stems are more supple as they have warmed up during the course of the day.
• There are additional benefits of growing vertically, including better light levels and, through targeted pruning and removal of side shoots, better air circulation.
• Bush, or determinate tomatoes don’t need nearly as much attention. They are much shorter and stockier than vining tomatoes, but even these types will benefit from some sort of support, particularly as the plants get laden with heavy fruits.
• In all cases, the aim is to keep the plants up off the ground to reduce the risk of diseases spreading and fruit rotting where they touch the soil.

Pruning Tomatoes

Another way to manage disease risk is to cut off the lowest leaves of your tomato plants.

• Ideally, we don’t want any leaves coming into contact with the soil, so prune out leaves to keep them well clear of the soil surface.
• Once plants are more established you can remove all the leaves up to the first flower/fruit truss. Doing this also helps with airflow, a good thing as stagnant air is a prime breeding ground for air-borne disease such as blight.
• Vining tomatoes will need any sideshoots removing. Also known as ‘suckers’, they will appear where the leaves join the main stem and it’s important to remove them in order to concentrate more of the plant’s energy on fruit production and to avoid issues with overcrowding and reduced airflow. 
• Pruning and sideshooting is best done in the morning as plants are more swollen after the cool of the night. This way they should snap off neatly, giving a clean break.
• In a cooler climate, you can prune once four trusses have formed on outdoor tomatoes, and once the main stem reaches the greenhouse roof for the tomatoes grown in there. 

Cover the Soil with Mulch

Work to achieve a healthy, nourished soil and the plants you grow in it will surely thrive! If you improved your soil before planting your tomatoes – such as an inch layer of compost – then you shouldn’t need to add any more compost over the course of the growing season. However, what you can add is a layer of mulch.

• Apply a mulch as talking – of shredded bark or grass clippings.
• Mulching has so many benefits: weed reduction, shaded soil for cooler roots in hot climates, moisture retention for more efficient use of water, and as a barrier between the soil and the foliage on your tomatoes, again reducing the disease risk. 
• When you water there is less chance of splash back onto the plants. And, of course, you won’t have to water as often.
• Mulches will also promote more even soil moisture, helping avoid issues such as fruit split – when plants are watered after a prolonged dry period, causing the fruits to suddenly swell and the skins to split open under the resulting pressure.
• Steady soil moisture also prevents blossom end rot, when calcium fails to reach the fruits due to a lack of water flowing through the plant.
• You can also grow tomatoes in straw bales, so they won’t need mulching. The bales also offer more consistent conditions at the roots.
• If you are growing in containers or growbags, please be sure to never let the potting mix dry out. Potting mix is a pain to rewet after it’s dried out, so try to prevent this happening in the first place. An irrigation system may help, as will growing in larger containers, which are slower to dry out. And remember you can also mulch the surface of potting mix in the same way as the soil.

Water and Feed Well

So how often should you be watering? The answer is: it depends! 

• In temperate climates, water tomatoes in containers at least once a day if it’s warm and dry, dropping to maybe twice a week in cooler, cloudier weather. Tomatoes grown in beds and borders will usually need watering less often. Of course, if you’re in a hot climate then you’re going to be watering more often than this.
• Do the finger test. Stick a finger down where the roots are – perhaps an inch or so beneath the soil surface, beneath any mulch, and assess how damp it is down there. If it’s dry, water. If it’s damp, don’t. Over time you’ll get a kind of sense for how moist it’s likely to be.
• Avoid wetting the leaves at all costs to reduce the chances for diseases to get a foothold. Try not to splash back soil or potting mix onto the leaves – this is where pruning and mulching help.
• Tomatoes are quite hungry plants. Plants grown in soil improved with plenty of compost may not need additional feeding, but plants in containers, grow bags and straw bales certainly will.
• Use a purpose-sold liquid tomato feed for this because it will have a good balance of nutrients specifically suited to tomatoes and other fruiting vegetables.

Reduce the Risk of Blight

Blight is the most widespread threat to our tomatoes. It’s notorious for cutting down plants in their prime, dashing hopes of summer-long harvests. This soil-borne disease is carried on the wind, so it’s just about everywhere. But there are precautions you can take to try and avoid it.

• Make sure to water carefully – taking care not to wet the leaves – and water in the morning if you can, so the soil surface has a chance to dry off during the course of the day.
• As mentioned earlier, cut off the lowest leaves so there is no foliage in contact with the soil and soil can’t splash up onto the leaves when you water.
• Encourage that all-important airflow. Pruning off those lower leaves and side shoots will help, but make sure plants are properly spaced too. If you’re growing in a greenhouse or tunnel, open up the doors, vents and windows as wide as they go to encourage a good ventilation. Tomatoes grown under cover will be less susceptible to blight, but they are no means immune, so watch out!
• Inspect plants regularly are remove infected material the very moment you spot it – act fast as blight spreads quickly.
• Avoid growing tomatoes near potatoes, as blight can pass between them, affecting both crops. Remove all traces of tomato and potato crops, including tubers, at the end of the growing season.

At this point it’s also worth mentioning one of the more common pests of tomatoes is the tomato hornworm. Hornworms weaken plants by eating the foliage. Being green in color, they don’t exactly stand out against the leaves, but a little tip is to head out at night and shine a blacklight or UV light on your plants. Incredibly the hornworms glow in the light, making them easy to spot and pick off.

See our video on Top Tips for Trouble-free Tomatoes which demonstrates many of the points discussed above!

Taken together, these simple steps should power your tomatoes through the growing season, giving you truly trouble-free plants and a delicious harvest.

If you’d like to know more about growing tomatoes, see the Almanac’s Tomato Growing Guide. 

And if you do run into trouble, see these top 10 tomato problems and solutions!