Preventing Rotten Tomatoes
One of the greatest joys in summer is
to harvest your first ripe tomato —
unless the tomato is rotten.
Blossom end rot is the No. #1
threat to tomato plants in our gardens
today. Our drought has made matters
much worse this year.
Blossom end rot is most often
associated with a lack of calcium in
the fruits. Without enough calcium in
their cell walls, the tomato fruits
collapse at their bottoms.
Blossom end rot also is associated
with drought, high temperatures and
low humidities. All of these factors
are occurring throughout North
Dakota.
What’s the answer? We need to
get more calcium to the fruits.
Some gardeners try to prevent this
rot by adding calcium to the soil.
They sprinkle eggshells and Tums
near the plants. This approach isn’t
bad but does little good because most
soils in North Dakota have an
abundance of calcium already in
them.
Other gardeners add Epsom salts
to the soil, but the magnesium in
Epsom salts may worsen the
situation.
The best strategy to reduce
blossom end rot is to irrigate
properly.
The uptake of calcium in the soil
by tomato roots depends on the
uptake of water. Irrigate regularly.
Avoid extremes of waterlogged and
droughty soil. Mulch to maintain
consistent levels of moisture in the
soil.
Cultivate shallowly. Don’t damage
the roots of your tomato vines. We
need these roots to absorb the
calcium in the soil solution.
Your fertilization practices can
make a difference. Do not
overfertilize.
Tomato leaves compete with
tomato fruits for calcium in the vine.
Overfertilization will lead to vines full
of leaves that will take calcium from
the vine before fruits can get it.
As a general rule, do not sidedress
tomato vines until their first fruits are
set.
Avoid fertilizers containing
ammonium nitrate, a very common
source of nitrogen. Ammonium ions
compete with calcium ions for the
limited areas on roots where nutrients
are absorbed. Calcium nitrate is a
better choice.
Calcium sprays are available that
may prevent blossom end rot, but
their effectiveness is inconsistent.
Follow the instructions on the label.
The bottoms of tomato fruits may rot due to a lack of calcium.
You can prepare your own spray if
you want to give it a try. Mix 4
tablespoons of calcium nitrate per
gallon of water. Spray fruits, not
leaves, two to three times a week. The
key time is when tomatoes are dime-
sized or smaller.
Now is a good time to inspect
your tomatoes to see if they are
rotten. The first cluster of fruits is
most often damaged. Remove any
rotten fruits.
Subsequent clusters of fruits are
much less susceptible to blossom end
rot. As summer progresses, the vine’s
network of roots expands, allowing it
to absorb more calcium into the
plant. The leaves and fruits on the
vine are in better balance later in
summer, too.
Focus your attention on irrigating
your garden when needed and don’t
overfertilize. Soon you will be
enjoying lots of tasty tomatoes this
summer.
2 NDSU Yard & Garden Report August
