Thursday, June 24, 2010

Early Summer Tomato Troubles

The cool, damp spring is still with us....even though it's 90 degrees, dry and officially summer. The harbinger of that recent past? The backyard tomato crop. Take a close look at those ripening red orbs that you planted during a drizzly April and early May.
Do they look like this?

Fruit Cracking
Or this? 

Or like this?
Solar Yellowing

Soon... they may look like this!

Blossom End Rot

The first two conditions, fruit cracking  and bacterial speck, you can blame on the cool, wet spring weather. 

That third condition, solar yellowing, is just what the name implies: too much hot sun, too soon.

That fourth ugly example, blossom end rot? A combination of weather, irregular watering, and lack of calcium uptake.

Another weather related malady: lack of tomato fruit set.

FRUIT CRACKS are tomatoes with deep ridges, radiating from the stem. When a wet spring suddenly turns to summer, those hot, sunny days may deplete more soil moisture than you anticipated. Radial cracking can occur during alternate rainy and sunny periods, such as what we had in May. Fruit exposed to the sun may also develop cracks. Maintain a uniform water supply. Mulches can help maintain that uniformity. A full leaf canopy will also help protect fruit from the sun and reduce cracking.

BACTERIAL SPECK: Hits during rain or overhead irrigation early in the season, during cool weather. Retards growth, reduces yields up to 25%, fruit spots, leaf spots. Leaf spots are near the edge of the leaf, dark brown with a yellow ring. Can spread throughout the leaf margin area. Common in cool coastal areas of CA. Solution: plant later in the season; avoid overhead watering.

Blossom end rot. According to the University of California, Tomato plants with blossom end rot show small, light brown spots at the blossom end of immature fruit. The affected area gradually expands into a sunken, leathery, brown or black lesion as the fruit ripens. Hard, brown areas may develop inside the fruit, either with or without external symptoms. Blossom end rot results from a low level of calcium in the fruit and water balance in the plant. It is aggravated by high soil salt content or low soil moisture and is more common on sandier soils.  Too much nitrogen fertilizer can also be a factor. Improper soil pH may play a role; tomatoes prefer a pH range of 6.0-7.0. To reduce incidences of blossom end rot, make sure that the root zone neither dries out nor remains saturated. Follow recommended rates for fertilizers. Some varieties are more affected than others. The disease is not caused by a pathogen. Although UC says there are no pesticide solutions, some gardeners believe that calcium sprays intended for this purpose offer some relief. My solution: avoid varieties that have betrayed you in the past, especially paste tomatoes.

SOLAR YELLOWING. According to the  UC Davis, Vegetable Research and Information Center , the reason for the yellow or yellow-orange color, rather than the normal red, is that the red pigment (lycopene) fails to form above 86 degrees (F). This phenomenon was first described by researchers in 1952 and was later confirmed by others. When lycopene fails to form, only carotenes remain for fruit color. An orangey-red color results. In production areas where temperatures do not exceed 85 degrees (F), much higher red color develops.

Failure to Set Blossoms. If you're lucky, your tomato plant has more to it than this picture right now. Among the reasons your tomato plant may look healthy, but lack fruit and blossoms:
Night temperatures are too low (below 55);
Day temperatures are too high (above 90);
Tomatoes were planted too early in the season; 
(late April-mid-May is best tomato planting time here in the valleys, foothills and Bay Area of Northern CA);
Too much nitrogen fertilizer;
Plants are in too much shade;
Tomato variety isn't adapted to California's hot summers;
Early season blossoms are not good fruit setters.

What's an impatient gardener to do about a lack of tomatoes?

Hormone sprays, designed to help deter blossom drop on tomatoes, is more effective at improving fruit set if the reason is low nighttime temperatures. According to the University of California, those sprays will not help in high temperatures. 
Another strategy: hand pollinate your tomatoes. When you see open tomato blossoms, gently shake or tap stems during mid-morning, three times a week. This can help fruit set during the late spring and early summer.

To avoid too much nitrogen fertilizer, choose a vegetable or tomato fertilizer that has relatively low amounts of nitrogen, phosphorus and potassium (as represented by the three prominent numbers on the front of most fertilizer containers). Choosing an organic fertilizer for tomatoes and vegetables, such as a 5-7-3, is a safe bet. Read and follow all label directions, no matter which fertilizer you choose.

More tomato growing info for the home gardener: UC Davis, Vegetable Research and Information Center


  1. Unfortunately about half my plants are too small to have any fruit and have very few blossoms. They are victims of the cool, wet spring.

  2. The timing of your post was right on. Our tomatoes seem to be slow in developing blossoms. You give me some clues as to the cause.

  3. So many variables! I can tell you that one of the Oxhearts is doing VERY well (it may be the B). It's growing fast -- producing multiple fruitsets at every level. I could not ask for more. As for the others? Not so much. The MP formed two early tomatoes -- but hasn't produced anything else yet even though it's tripled in size. Perhaps my IV with direct Miracle Grow crystal injection wasn't such a good idea after all.

    You do know I'm kidding. I hope.

    As for my plants? Hardly any fruit set that I can see. But they're just getting to that stage where they should start setting something. I've got to keep reminding myself that I delayed plantout for six weeks...

  4. Just picked my first tomato (Banana Legs) last night. It had a crack on the side, but was otherwise perfect. Checked the drip &, sure enough, the emitter had somehow been moved far enough that it wouldn't be doing much good. Hopefully the next few will be crack-free.

    If only I had an answer to why my massive Cherokee Purple rotted ! It was huge, just beginning to color up when it developed a soft spot on its side that soon made it obvious the whole fruit was a loss.

  5. Great info! I will further inspect my tomatos. I do have alot of fruits on my Black Krim, about the size of golf balls, so far so good. I have lots of flowers on the rest of my plants. Im still awaiting flowers on my Mortgage Lifters, the plants are still very small. They are in an area thats only getting 6 hours of sun.

  6. Tomatoes listed in the catalog as "early" or that have a shorter days-to-maturity generally set and ripen better in cool weather: Early Girls, Black Prince, Cherokee Purple, etc. Those listed as "main season", "late" or that have long DTM are not going to do well in a year like this one.

    Plant a mix of the two and you will be more likely to get a longer harvest season in a normal year, and a better chance of getting any tomatoes at all in a challenging year like this one or a year of excessive heat.

  7. I thought I had some type of worm before I found this article. I have a slight case of bottom end rot. Going to try a few of these ideas. Thanks for posting.