Remember the excitement of planting those tomato seeds back in the depths of the rainy season?
It probably looked like this: A chilly February morning in the Pacific Northwest, the sky is a muted gray. But inside, your tiny seedlings are glowing under the warm, artificial sun of your grow lights. You carefully rotate the pots, ensuring each young plant gets its fair share of light. You run a fan to mimic the gentle spring breeze, strengthening their tender stems. Each morning, you greet them with the same anticipation you felt as a child on Christmas morning, hopeful for a bumper crop.
Fast forward a few months, and the foggy mornings have given way to the rare yet glorious PNW summer sun. You've carefully hardened off your seedlings, watching them adapt to the outdoor world. The last frost has finally passed, and your precious tomato plants are now thriving in the garden, ready to bask in the sun/rain/sun cycle typical of our region.
But then, on a seemingly perfect dry summer day, you notice something startling while tending to your tomato plants—unusual spots and curling leaves! WTF (what the foliar…). Is it blight? Are all your tomato dreams shattered, like a mason jar full of tomato sauce that got too hot in the pressure canner?
Don't worry just yet. You’re keen. You’re smart. You're here and so you’re already one step ahead. Many of these issues have straightforward solutions, and some may not even signify a problem at all.
Let’s take a diagnostic approach to interpret what your tomato plants are trying to tell you. We'll look at what Pacific Northwest-specific issues might be causing these behaviors, and give you actionable solutions to keep your tomatoes in tip top shape.
Those cool damp springs that come standard in the PNW can unfortunately be a hospitable environment for fungal diseases, such as early blight and Septoria leaf spot.
North Carolina Extension Service notes that Septoria leaf spot is most severe when temperatures are mild (60-80°F or 15-27°C), rainfall is frequent, and relative humidity is high. Sound familiar?
Clemson University shares similar information for early blight, which favors temperatures between 59-80°F (15-27°C) and high humidity or leaf wetness.
Our cool, damp springs in the PNW are prime breeding grounds for both of these diseases.
If you see brown spots or speckling on your plants, it can be a sign of fungal infections. University of Wisconsin-Madisondescribes the fungal disease of Septoria leaf spot as “circular, tan-to-gray spots with darker brown margins.” It can be paired with dark specs encased in a yellow circle, and shows on lower leaves first.
Solution:
Tip:
Plant a hairy vetch cover crop after your tomato harvest to prevent fungal and other disease issues from occurring in the future, and practice crop rotation. For best results, don’t plant any other nightshades (i.e. peppers, eggplants, potatoes) in this spot for another 3 seasons.
Wilting can indicate several problems, including root rot, verticillium wilt, or inadequate watering.
While our springs and falls are notoriously wet, our summers can be filled with lengthy droughts. During this time, regular watering is important to prevent wilting tomato leaves.
Solution:
Tip:
If plants are stressed from not enough water, consider applying mulch like grass clippings or organic straw to help prevent water evaporation.
Often a sign of phosphorus deficiencyor cold nighttime temperatures.
Oregon State University describes the typical clay soil of the region
While we usually have great sleeping weather in the PNW, those cool nights can be the cause of this foliar issue.
Solution:
Tip:
Certain plants have naturally high levels of phosphorus in their leaves, which can be turned into a nutritive compost tea. Recent study found leaves of Lamb’s Quarters, lettuce, and amaranth to be particularly high in phosphorus. Bone meal works well too.
This can result from viral infections (like tomato mosaic virus), or pest attacks (e.g., aphids. Interestingly, WSU shares that aphids spread this virus around to plants.
In another source, WSU says, “Virtually every crop grown in Washington is used as a host by one or more species of aphid.”
Solution:
Tip:
As the University of Florida states, “Plant viruses cannot be cured, hence management efforts should be directed toward reducing virus spread.” Frequent observation of your plants can help remove troubled plants before the issue spreads throughout your whole summer crop.
The Department of Plant Pathology at the University of Kentucky describes this as a frequent occurrence when tomatoes are in heavy production mode. This can indicate nutrient deficiencies (especially magnesium).
Washington State University shares that both calcium and magnesium is usually in low quantities in soils west of the Cascade range.
Solution:
Tip:
Nettle compost tea can boost magnesium levels.
These can be caused by sunburn, fungal infections (e.g., Early Blight), or nutrient imbalances.
Solution:
Tip:
NC State Extension recommends that you water plants at the soil surface and mulch around plants with grass clippings or organic straw to help prevent blight in the soil from splashing up onto your plants.
UFL notes that this is often a sign of spider mite infestation.
While many of the issues outlined in this article are due to the Pacific Northwest’s wet springs, spider mites thrive in our dry summers. Nicole Sanches, OSU Extension Service Master Gardener, shares that “hot, dry, dusty weather is ideal for spider mites.”
Solution:
University of Maryland Extension Master Gardener Gerald Brust shares that this is caused by excess water uptake and poor transpiration.
It can be especially common when growing tomatoes under cover, like is usually recommended for Pacific Northwest gardeners.
Solution:
White, powdery spots on leaves, stems, and buds.
Like other fungal diseases, powdery mildew can be prevalent in the PNW. Northewest Center for Alternatives to Pesticides says, “When the weather is mild, which is not uncommon during the mild summers of the Pacific Northwest, many plants will be vulnerable to attack. Stay vigilant!”
Solution:
Tip:
Plant resistant tomato varieties and keep the garden area clean of debris. NWCAP offers some solace: “Many plants will be able to outgrow it, or live through it with only somewhat lower yields or quality.”
Dark brown to black spots on leaves with a fuzzy white growth on the underside during wet conditions.
The NW Potato Research Consortium tells us, “Late blight is a historically famous plant disease that can be very serious in Western Washington.”
Solution:
Tip:
Plant blight-resistant varieties and space plants properly to improve air flow.
Slugs are a PNW gardener’s #1 enemy. They leave irregular holes in leaves that can add up fast. Solution:
Tip: Water in the morning to reduce evening moisture, which attracts slugs.
White or yellow patches on leaves and fruit.
Solution:
Tip: Use shade cloth or plant taller companions to provide natural shade.
Sometimes leaves curl due to environmental stressors like heat and wind but do not signify a major issue.
Just like a person might curl up under stress, tomato plants occasionally curl their leaves due to environmental stressors. If they are otherwise healthy and producing fruit, there's no need for alarm
Observation: If the plant is otherwise healthy and producing fruit, occasional curling is usually not a concern.
As tomato plants grow, it's natural for older leaves at the base to yellow and drop off.
Think of it as a natural shedding process, much like trees losing leaves in autumn. As the tomato plant focuses its energy on new growth and fruit production, it's natural for older leaves at the base to yellow and drop off.
Observation: This is part of the normal lifecycle of the plant, especially as it focuses energy on new growth and fruit production.
Young tomato plants sometimes develop crinkly or ruffled leaves as they grow.
Observation: If the plant continues to grow normally and appears healthy overall, this is typically not a cause for concern.
Directly after your tomato harvest, plant a hairy vetch cover crop. This cover crop has been shown in studies to reduce instances of Fusarium Wilt, Powdery Mildew, and Blight. Hairy vetch also attracts beneficial insects that will eat aphids, like lacewings and ladybugs. Hairy vetch germinates best in moderate temperatures, so plant as soon as you can in September or October. Here’s more about how I am improving the soil of my greenhouse with hairy vetch.
Note where you planted the tomatoes and don’t plant any other nightshades there for 3 years. This will help prevent pest and disease build-up in the soil. After your hairy vetch cover crop, plant a spring crop of broccoli or beets, followed by a summer crop of bush beans. Try out a winter rye cover crop, and then go for cucumbers, winter squash, or zucchini the following year. Next year, try some early spring carrots followed by summer salads. One more cover crop and then you’re ready for tomatoes to be in this same spot again!
Stock up on organic straw mulch and apply this to the soil around your tomato plants to prevent disease spread and to retain moisture during our dry summers.
This keeps water at the base of the plant to avoid splashing, and will keep your plants hydrated with less water during the dry heat of the summer.
The PNW is well known around the world for our various mushrooms that grow in our verdant forests. But did you know that a mycorrhizal inoculant can help improve the overall health of your tomato plant? These beneficial fungi friends help with nutrient and water delivery to your plants and can help them fight off disease. Two summers ago, I noticed that tomato plants that received myrorrhizae at transplant made absolutely gigantic fruit! Try this OMRI certified brand.
Planting nasturtiums or marigolds around tomato plants can attract aphids, slugs, and other pests, diverting them from the main crop.
Oregon State University recommends, “Choose early maturing varieties, 80 days or less. If you are close to the ocean, fewer days is better. For our climate, yo ushould add about two weeks to the states days to maturity.”
(note that all info comes from the seed company directly linked)
Wheatly’s Frost Resistant Grape Tomato:
Minusinsk Lion Slicing Tomato:
Cuor di Bue Albenga Paste Tomato:
Moutaineer Delight Slicing Tomato:
Once you understand the leaf language of your tomato plants, you can jump into action to stop any issues before they become serious. Daily observation can help you track when any problems arise so that next year, you can prevent issues before they occur - or not freak out over something totally normal.
1. Why are my tomato leaves turning yellow?
2. How often should I water my tomato plants in the PNW?
3. What are the best tomato varieties for the PNW climate?
4. Can I grow tomatoes in containers in the PNW?
5. How do I prevent fungal diseases in my tomato plants?
6. When should I start my tomato seeds indoors?
7. What should I do if my tomato plants are not setting fruit?
Problem: Tomato Leaves Are Wilting
Problem: Tomato Leaves Have Brown Spots or Speckling
Problem: Tomato Leaves Are Turning Purple or Red
Problem: Tomato Leaves Are Twisted or Distorted
Problem: Tomato Fruits Have White or Yellow Patches (Sunscald)
Problem: Tomatoes Have Irregular Holes (Slug and Snail Damage)
Problem: Tomato Leaves Have a White, Powdery Coating (Powdery Mildew)
Problem: Tomato Leaves Have Interveinal Chlorosis (Yellowing Between Leaf Veins)
