Undoubtedly, the main reason tomatoes are so widely
grown is that home-grown tomatoes taste so much better than their
store-bought counterparts. But another reason is the intrinsic vigor and
hardiness of this nightshade relative, which almost always guarantees a
successful harvest. However, the rapid growth of a healthy tomato plant
can also lead to problems.
Like all plants, a tomato is a solar-powered
sugar factory. For the first month or so it's in the garden, all of the
sugar it produces is directed towards new leaf growth. During this
stage, tomato plants grow very rapidly, doubling their size every 12 to
15 days. Eventually, the plants make more sugar than the single growing
tip can use, which signals the plant to make new branches and to flower.
This usually happens after 10 to 13 leaves have expanded, at which time
the plant is 12 to 18 inches tall. In the next few weeks, the entire
character of the tomato plant changes. If unsupported, the increasing
weight of filling fruit and multiple side branches forces the plant to
lie on the ground (see
spacing options). Once the main stem is horizontal, there is an
increased tendency to branch. Left to its own devices, a vigorous
indeterminate tomato plant can easily cover a 4- by 4-foot area with as
many as 10 stems, each 3 to 5 feet long. By season's end, it will be an
unsightly, impenetrable, disease-wracked tangle.
Prune for plant structure and health
With tomatoes, we want to maximize the
efficiency of photosynthesis and minimize the risk of disease. This is
best accomplished by ensuring that each leaf has plenty of room and is
supported up off the ground. When a tomato plant lies on the ground, or
when its growth is extremely dense, many of its leaves are forced into
permanent shade, greatly reducing the amount of sugar they produce.
There is no free ride in the plant world. If a leaf uses more sugar than
it makes, a layer of abscission cells develops between the main stem and
the leaf petiole; eventually the leaf yellows and drops. Of course,
sloughed-off leaves are replaced by new ones, but time is wasted.
Prostrate plants get around to fruit production two or three weeks later
than a pruned and staked plant. Most of the fruits they do produce are
on the small side, and tend to come in one big, late harvest.
Get plants off the ground.
Give plants room.
Never prune or tie plants when the
leaves are wet.
A properly pruned and supported single-stem
tomato plant presents all of its leaves to the sun. Most of the sugar
produced is directed to the developing fruit, since the only competition
is a single growing tip. The result is large fruits that are steadily
produced until frost. If more stems are allowed to develop, some of the
precious sugar production is diverted from fruit to multiple growing
tips. Fruit production, although slowed, never stops. The result is a
nearly continuous supply of fruits throughout the season. In general,
more stems means more but smaller fruits, which are produced
increasingly later in the season. (This is much less applicable to
determinate plants, due to their shortened growing season and
better-defined fruiting period. Therefore, determinate plants require
Pruning also affects plant health. The leaves of a
pruned and supported plant dry off faster, so bacterial and fungal
pathogens have less opportunity to spread. Soil is less liable to splash
up onto staked plants. The bottom line: Upright plants have fewer
problems with leaf spots and fruit rots because their leaves stay drier
and free from pathogen-laden soil.
The way you choose to train and prune your tomato
plants will affect how you space your plants, as well as the best method
of support . There's no one right way to do it. Instead there are a few
good patterns to follow.
Side stems affect plant vigor
As a tomato grows, side shoots, or
suckers, form in the crotches, or axils, between the leaves and the main
stem. If left alone, these suckers will grow just like the main stem,
producing flowers and fruit.
Suckers appear sequentially, from the bottom of the
plant up. The farther up on the plant a sucker develops, the weaker it
is, because the sugar concentration gets lower as you move up the plant.
On the other hand, side stems arising from below the first flower
cluster, although stronger, compromise the strength of the main stem.
For a multi-stemmed plant, your aim is to have all stems roughly the
same size, although the main stem should always be stronger, because it
has to feed the entire plant for the next five or six months. Here's how
I achieve this.
I keep tomatoes free of side stems below the first
fruit cluster. When trained to one vine and left free-standing, tomato
plants develop strong main stems. To encourage a strong stem, I remove
all suckers and I don't tie plants to their supports until the first
tomatoes need no pruning other than removing all suckers below the first
flower cluster, because pruning won't affect their fruit size or plant
vigor. If you do any pruning at all above the first flower cluster on
determinate tomatoes, you'll only be throwing away potential fruit.
tomatoes can have from one to many stems, although four is the most I'd
recommend. The fewer the stems, the fewer but larger the fruits, and the
less room the plant needs in the garden. For a multi-stemmed plant, let
a second stem grow from the first node above the first fruit. Allow a
third stem to develop from the second node above the first set fruit,
and so forth. Keeping the branching as close to the first fruit as
possible means those side stems will be vigorous but will not overpower
the main stem.
Simple vs. Missouri pruning
There are two ways to deal with a sucker that
isn't destined to become a stem. The simplest is to pinch it off
entirely; not surprisingly, this is called "simple pruning." This should
be done when the sucker is still small and succulent. Grab the base of
it between your thumb and index finger and bend it back and forth. The
sucker should snap off, producing a small wound, which will heal
quickly. Avoid cutting the sucker with a knife or scissors, because the
resulting stump can become easily infected. Once a sucker becomes too
tough and leathery to snap off, however, you'll have to use a blade. I
recommend a retractable razor knife.
In Missouri pruning, you pinch out just the tip of
the sucker, letting one or two leaves remain. The advantage is that the
plant has more leaf area for photosynthesis and to protect developing
fruit from sun-scald. The disadvantage is that new suckers inevitably
develop along the side stems, adding to your future pruning chores.
Personally, I prefer Missouri pruning, despite its shortcomings. I
relish revisiting each Missouri-pruned side stem, repeatedly reinforcing
my initial godlike decision to cut or not to cut. Either method works,
though, so enjoy your newfound power.
Missouri pruning is necessary when things have
gotten out of hand. When you're dealing with large suckers, it's better
to pinch off just the tip than to cut off the whole thing close to the
main stem. For one thing, if disease hits, it's farther away from the
main stem. And for another, removing just the growing tip is less of a
shock to the plant than removing a foot or so of side stem.
You'll find that suckers grow very quickly during
the hot summer months. I can't count the times I've returned home from a
five-day road trip in July to find my formerly well-tended tomatoes
covered with foot-long suckers growing in all the wrong directions. This
is indeed a situation that tests one's resolve. It helps to know that
side stems started this late in the season will always be spindly and
produce inferior fruit. You must be heartless and tip them all.
Blest be the tie that doesn't bind
Once flowering commences, all tomato
vines must be tied to their supports. Although vigorous, the plants are
also easily damaged, so take care in how you tie them and what you use.
Cloth strips work well as long as they're not too old and threadbare.
Pieces of panty hose cause the least damage to plants, but they're not
biodegradable. Twine should be at least 1/8 inch thick, or else it can
cut into the tomato stems. Twine made of natural fibers like jute or
sisal will break down sufficiently over winter not to cause problems
with tiller tines, as panty hose would.
There are two types of ties. Training ties direct
plant growth upwards, and supporting ties keep it there. The top foot of
a tomato stem, or leader, is very succulent and easily snapped; it needs
to be directed upwards, gently. I wrap a short piece of twine around the
middle of the leader, cross it over on itself, and loosely tie it to the
support. The resulting figure-eight tie reduces the chance the tender
stem will rub against the support and get bruised.
Fruit will form along this stem. If left to
the devices of the loose training ties, the weight of the fruit will
pull the ties down the stake. Eventually, the stem will bend over and
crease. Luckily, as the stem matures, it toughens; by the time fruit
develops, the stem can tolerate a tighter tie. To support a fruit
cluster as it fills and gains weight, I loop a longer piece of twine, 12
to 18 inches, around the stem just above the fruit cluster, creating a
sling. Then I gently pull it up to take the weight off the stem. I wrap
the twine twice around the stake, and firmly tie it to the stake 6 to 10
inches higher than the point of attachment to the vine. To keep the tie
from slipping, I knot it underneath the point where the sling meets the
A final pruning pays off
Later in the season, about 30 days before
the first frost, there is one last pruning chore. The plants must be
topped. The fruit that has set must be given every opportunity to
mature. To this end, I direct all carbohydrates produced by the plant to
the fruit by removing all the growing tips. This, too, can be hard to
do. Every gardener is reluctant to admit the season is coming to an end.
However, this final pruning can make all the difference between hard,
green fruits, hurriedly picked before frost, which later rot in a paper
bag, and ripe, home-grown tomatoes in your Thanksgiving salad. Be tough,
fight your nurturing instincts, and top those plants.