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Monadnock Grows Together: Tomato Health

​Hello Garden Friends!

I wanted to share some thoughts with you about tomato health in general, and also about late blight in particular.

Tomatoes are not particularly difficult to grow, but like most plants they do have health needs. Plant health starts with the soil; generally it’s a good idea to have your soil tested every two years. Tomatoes in particular are “heavy feeders,” which means they like a lot of nitrogen. They also need phosphorus and potassium; together these three nutrients are often labeled NPK. In addition to NPK, tomatoes (like all plants) need micronutrients like calcium, copper, magnesium, potassium, and more. Healthy soil will likely provide all of these things to your tomatoes; you can also add a good quality compost as an amendment. If you are curious to learn more about homemade organic fertilizers you can feed your tomatoes and the rest of your garden, check out this page.

All tomatoes need some kind of physical support. This could be a tomato cage, a stake, a trellis of some kind, a fence… your creativity is the limit, just keep those plants off the ground. Tomatoes need to be trimmed as well, and it’s best to make this a regular habit so it doesn’t become overwhelming. Primarily, you’ll want to regularly remove the suckers (see diagram below). I also like to trim the bottom leaves so the plant isn’t touching the ground.

Tomatoes need consistent moisture, particularly when they’re setting fruit. Straw mulch can help with this, and can also prevent soil from splashing up on to the tomato’s leaves. You can also explore passive watering techniques; read more about those here. When it comes to watering, the best time of day to do this is in the morning, so the plant has time to dry off during the day. Do your best to water the ground, rather than the plant itself.

You have likely noticed that I’ve mentioned keeping the plant off the ground and soil off the plant a number of times. This is to help with disease prevention, particularly fungal diseases, of which late blight is one.

Late blight, or Phytophthora infestans is a highly contagious fungal disease that affects tomatoes and potatoes. It usually comes around later in the season, when the weather is humid. It can be spread through direct contact, soil contact, and the spores can be blown through the wind. Prevention is the best way to handle late blight.

Consider planting blight-resistant tomato varieties; often plant tags or seed catalogs will indicate if a particular varietal is disease resistant. This is quite a good article on blight resistance, and includes a long list of resistant varieties.

When you plant your tomatoes, plant them with enough space to ensure good air flow between the plants. This will decrease the likelihood of catching late blight and spreading it through your plot. Keep your tomatoes well-trimmed and off the ground. Use a mulch to keep soil from splashing up onto the plant. Water in the morning, and try to water the ground rather than the plant.

Monitor your plants closely and regularly. If you do notice signs of late blight on your tomato plants (leaves with dark, water soaked patches, that turn dry, brown and papery; possible ring of white mold; stems that turn black; fruit with large, irregular, brown, greasy-looking spots) (from The Organic Gardner’s Handbook of Natural Insect and Disease Control, by Barbara W. Ellis and Fern Marshall Bradley), remove the affected parts of the plant at once, double bag them in plastic, and throw them in the trash. Do not compost them; this will spread the disease. Apply a foliar spray of compost tea; you can make some yourself by putting a gallon of well-rotted manure-based compost into a five gallon bucket, filling it with water, letting it sit in the sun for a few days, and then straining out the solids. Apply the tea in the evening. Check your plants regularly, as you may need to follow this procedure a number of times. You may also want to consider a copper spray; your local garden center should supply this.

When it comes to late blight and other fungal diseases, prevention and control are the focus. There is no cure. Additionally, it’s very important to watch for blight on your tomatoes or potatoes; it is highly contagious (yes, I’m repeating myself – this is important!) and can easily spread to other gardeners’ or farmers’ plots. Caring for your garden also means you’re caring for your community’s gardens!

If you want to read more about late blight and other fungal diseases in tomatoes, UNH extension has a really great article on the topic. They are a great go-to when researching garden problems!

I don’t want to scare you away from growing tomatoes! Being well-informed is the best way to be prepared for potential problems. The most important thing to do in your garden and with your tomatoes is to HAVE FUN and keep learning and growing!

If you have questions, comments, or stories you’d like to share about your garden or your tomatoes, please do – I’m looking forward to hearing from you!

Happy Growing!

Written by: Rachel Brice

Urban Ag & Gardens Coordinator


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