Article and photos by Rob Danforth

We keep tomatoes up, off the ground, to avoid problems, we keep the plants free from competition from weeds and bad companions, we make sure their soil is continually moist, we aerate the soil to get air to the roots, and we trim the plants to ensure air flow, to restrain growth, and concentrate plant energy in a limited number of fruit.  However, if you plant them, problems may come.


Proactive strategies:

  1. Ensure that the soil is healthy with generous additions of compost or non-burning fertilizer with calcium.
  2. Reduce weed pressure by weeding regularly and/or by adding mulch – all naked soil in pot or plot is fertile ground for weeds which compete with the tomatoes for plant food.
  3. If you have added home grown mulch, watch for volunteer plants (e.g.: tomatoes, squash, sunflower, dill) which may sprout from seeds in the compost and compete for plant food.
  4. Water roots only and not the leaves.  Wet leaves attract and hold bacteria and fungus spores.  A watering can is recommended so leaves do not get wet, you can ensure each plant was watered twice, and you can check each plant for wind damage, insects (e.g., tomato horn worm; Colorado potato beetle), disease, side shoots, suckers, and nutrient deficiencies.
  5. Reduce bacteria and fungus on plants by reducing soil splash & keeping leaves from touching soil.  Remove lower leaves, and add a mulch.

Reactive strategies – Note:  weakened plants attract feeding insects, nature’s bio-janitors.   

  • Pale yellow or tawney colour in the leaves, usually starting from the center vein in a leaf, suggests a nitrogen deficiency. Add fertilizer with NPK (Nitrogen, Phosphorus, Potassium).
  • Yellow leaves, usually at the bottom first but could be anywhere on the plant can indicate that a plant is drowning. Reduce water as best you can.  Transplanting may be necessary.  Recovery will be slow!
  • Purple splotches on leaves indicate a phosphorus deficiency. Add fertilizer with NPK.
  • Tomato “blossom end rot” is a result of uneven watering which reduces calcium uptake and produces a calcium deficiency, not a disease. Remove affected tomatoes & compost them – do not let the plant waste energy developing inedible fruit.  In container or in-ground, add Epson salts and powdered milk (50/50 in 1/4 cup total) to the soil, rake the surface, & water in. You can also fertilize with chicken manure which contains calcium. Recovery will be slow.
  • Septoria: older leaves & fruit will show spots first. Add potassium to the soil.
  • Wilted leaves: plant is thirsty so add water and be on the lookout for blossom end rot. However, in a polytunnel, the wilt may be a result of cooking the plants – too much heat and humidity!  Give them air and good ventilation.  Recovery will be very slow.
  • Brown spots dotting the leaves may be early or late tomato blight. Leaves will eventually go all brown and crispy and dark spots like bruises can appear on the stems.  Clean up all debris, cut and green bin, trash, or burn all diseased parts.  Clean tools and gloves with hot soapy water, alcohol sanitizers, or diluted bleach to eliminate disease transfer. Blighted plants will still produce edible tomatoes, so cut away the blighted sections daily but allow the fruit to continue – this blight does not hurt people.  After surgery, a blighted tomato plant will ultimately look like a leafless vine with fruit dangling. Blight will remain in the soil for a few years.
  • Brown patches on the leaves and wizened tomatoes may be sun burn or sun scald! Do not trim tomato leaves too much so the tomatoes are naked (blight is the exception – trim it all!).  Reduce the strength of the sun with a sun screen.  Tomatoes need sun, but do very well in medium strength sun.
  • Ugly spots on the tomatoes (often on the tops) will be bacteria eating into the skin of the tomato. Remove the fruit and compost them or if the bacteria spread is not too great, cut off the affected areas and eat the tomato.

General garden notes: 

– Bacteria eats into the leaves and fruit starting with a small dimple on the surface, fungus clings to surfaces and has fruiting bodies that produce spores like mildew or furry looking growths, and viruses are systemic (i.e., inside the plant). Viruses cause structural deformation and noticeable colour variation in leaves and fruit, quite different from shapes and colours you expect.  Bacteria and fungus can be composted.  Viruses (e.g., mosaic virus) cannot be cured so eliminate entire plants (leaves, stems, fruits, and roots, as well as fallen plant debris) and do not compost.

– Tomatoes planted in the same soil year after year may do well for about 3 years in a row, but nutrients will be depleted, and blight will come! Then you will have to wait 3 years with many applications of compost before reusing that spot for tomatoes.  Rotation is the best strategy.  Tomatoes in containers (e.g., a “potato bag” or lard bucket with drain holes) can help with rotation.

–  Add compost to pot and plot 2x/year (e.g., fall or early spring & mid-season) to neutralize disease over time, balance pH, add nutrients (NPK + a great many essential trace elements), retain moisture, and keep the soil friable.

Nature’s wisdom:  if you are having persistent problems with certain types of plants (vegetables, herbs, or flowers) listen to what nature is telling you and consider growing only what will be successful in your soil and climate.  If at first … try and try again is not always the best advice.  Plant stress is one thing; gardener stress is quite another!

Happy Gardening!

DTE Tomato series:  Starting & Transplanting, Maintenance, Disease & Stress Management, Tomato Salvage & Seed Saving.