Protection for Tomato Skins
sun's rays are tough on our faces and arms, but we can wear sunscreen
to reduce the damage to our skin. Tomatoes don't have that option.
Exposed to bright sun, the fruit can heat up dramatically, reaching
temperatures as much as 18 degrees warmer than the surrounding air.
Sunscald damage to your tomatoes depends on their stage of maturity,
and the intensity and duration of the heat. The fruit is most
susceptible when it is green or when the first pink color begins to
show (called the breaker state).
the fruit's temperature exceeds 86 degrees Fahrenheit on its sunny
side, the flesh remains hard and will not ripen. At this temperature,
the fruit can't produce the red pigment, lycopene, but still produces
the yellow pigment, carotene. At a sizzling 104 degrees, the tomato
stops producing carotene and the damaged area turns white. Damaged
cells eventually collapse and the area may become sunken.
To prevent sunscald, maintain a healthy foliage cover. Keep plants
well-watered and free of pests and diseases that can reduce foliage.
Don't prune your tomato
plants and place them densely enough that they
can benefit from mutual shade. Keeping the soil cool with plenty of
water and mulch helps, too.
If you let
your plants sprawl on the ground, don't turn them to expose the
underside of the fruit. That's a common cause of sunscald.
Summer heat can also cause cracking in tomatoes. Radial cracks are most
common, starting near the fruit stem, and developing down the sides of
the fruit wall. Concentric cracks sometimes appear as circles around
the stem end of the fruit.
Cracking is most common during hot, rainy periods when temperatures are
in the 90s, particularly following long dry spells. It is most severe
on fruit that is ripening in full sun and plants that have been heavily
pruned. Those heavily pruned or that have lost foliage due to insects,
disease or weather will heat up and be most likely to crack.
To help prevent your tomatoes from cracking, use the same strategy as
for sunscald. Fertilize plants judiciously and encourage good foliage
cover. Mulch the soil around the plants and keep it consistently moist,
using drip irrigation instead of overhead impact sprinklers.
Some tomato cultivars, such as "Beafsteak-type" tomatoes, are known for
cracking, while others are more resistant. Cultivars like 'Early Girl,'
'Ultra Girl' and 'Springset' resist cracking.
Cheryl Moore-Gough, Montana
State University Plant Sciences
and Plant Pathology, (406) 994-6523
Vegetables from Self-Watering Containers
from the Farm
Many Varieties of Tomato
Farmer's Market Guide