FIMBY: What’s (already) wrong with my tomato plants?

The tomato plants have barely been in the ground a month, or two weeks, or three days — and already problems are showing up.

The good news is: At this stage in the season it’s not too late to fix most of the problems. And with other issues, the gardener has time to dump a  problem plant and start over, perhaps with a different variety, or in a different location or container. The really big problems occur mid-season when fruit forms (or doesn’t), the heat kicks in and the pesty insects appear.

But right now tomato gardeners have to be honest with themselves — is the problem really with the gardener? Too eager to water, or too neglectful? Let’s explore the topic.

Yellowing

— If the tomato leaves are yellowing all over, the plant might be overwatered or underwatered. That doesn’t sound helpful, but check the soil! Tomatoes — once established — do best with deep but less-frequent watering. If the soil is soggy, the plant might be drowning — especially if the leaves also are droopy.

— Are only older leaves yellowing? That’s actually a normal reaction to growth, especially if the plant is still in a small container. The plant is pulling nitrogen out of the older leaves into the newer ones. Those yellow leaves will never go back to green, so clip them off.  Get the plant into its final home, whether in ground or in a large container. Don’t fertilize it immediately, which can stress a plant, but make a note to give it some low-dose fertilizer within a week. Mulch with compost.

— If the leaves aren’t yellow so much as light green,  it’s stressed and needs nitrogen. This often happens if it’s been grown from seed but left in a container too long.  Get it planted in nice rich soil, baby it a little, and it will recover after the roots are acclimated.

Wilting

— Wilting doesn’t necessarily mean the plant needs water! It’s stressed, yes.  Underwatering is unlikely at this time of year — in that case the top will wilt before the rest of the plant. Wilting could be happening in concert with leaf yellowing, caused by overwatering.

Other causes are more troubling: Wilting diseases such as fusarium wilt or verticillium wilt can strike quickly, and what looked like a healthy plant yesterday may have entirely collapsed. Root-knot nematodes also can cause wilting. Sometimes just one side of the plant wilts! These diseases are spread through the soil and into the roots — which is why crop rotation is so important — and heirloom tomato varieties are often susceptible. Those VFN symbols on hybrid tomato tags or in seed catalogs indicate resistance to these diseases. 

What to do? The plant ultimately won’t recover, so carefully dig it out and discard it (not in the compost).  Avoid planting another tomato there unless certain it’s a disease-resistant variety.

Spots on leaves

— White spots the size of hole punch dots can mean bleaching by sun or raindrops on a plant that is not fully acclimated to outdoors. These plants will recover and grow out of the discolorations. Smaller white spots, like pin dots, can indicate the presence of aphids or spider mites, which are attracted to already-stressed plants. Spider mites prefer hot, dry weather, so keep an eye out for those as spring heads to summer.

— Dark spots indicate trouble.

Large dark spots appear on the lower leaves when rain splashes plants in humid weather — this could be early blight, a fungus. We typically have drier weather by late spring, but I do remember one damp June when suddenly several Sacramento tomato gardeners were reporting early blight. The plants can recover but drastic measures are required: Any leaves showing blight must be cut off and discarded. When the weather clears, new unspotted growth should appear. Mulching around the plants also helps avoid blight.

Septoria leaf spot also creates larger spots on leaves, often coinciding with early blight. This also is a fungus, also related to humid weather or overhead watering, but not a fatal one if caught early. Remove infected leaves, improve air circulation around plants, and mulch around them, too.

Dark pin dots all over leaves can mean bacterial speck or bacterial spot. These disease bacteria survive in soil, in debris from diseased plants (such as immature compost), and on seeds. Again, wet weather or overhead watering contributes to their spread. No cure, so remove the plants and discard; don’t compost them. Pin-dot holes, meanwhile, can mean the presence of flea beetles.

 Purple-tinged plants

This condition shows up in young transplants; the poor things need phosphorus, but should find it once planted in good soil, either in the ground or in potting soil boosted with compost. Remember to fertilize with a low-dose balanced fertilizer.

Leggy plants

Tomato plants grow leggy when they’re not receiving enough sunlight. This can happen when seedlings are kept too long indoors, or grow with inadequate light. The plant will be fine, but should be planted deeply, and not in the shade. New roots will grow along the buried stem, and the top of the plant will bush out. Very leggy plants even can be planted at a 90-degree angle in a shallow ditch, and the top gently angled vertically.

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Ready for a deep dive into tomato problems, including ones involving the fruit? This gallery and chart (scroll to the bottom) from the University of Maryland Extension is an excellent resource, with clear images. Remember, though, that Maryland is much more humid than Northern California; gardeners there have more problems with fungal diseases.