The question of "optimal" pruning of tomatoes is rife with contradictory opinions. Sometimes even contradictory facts! What is provably true for one variety, may be totally opposite for another variety. I am sharing what I have learned from a decade of growing in my AeroGardens, and extensive reading from Universities and agricultural services. But by all means, do your own research too! Try different methods on your own plants. There are lots and lots of variables that can affect your personal results.
Before we get to specifics, a bit on the overall pruning theory.
One of the important things to remember, is that most tomato pruning advice out there is for indeterminate varieties, as that is the vast majority of "regular garden" tomatoes. However, nearly all varieties that are suitable for growing in hydroponics in general, and AeroGardens specifically, are determinate simply by virtue of being microdwarfs. To my knowledge, all microdwarfs are determinate - otherwise they would just keep growing and no longer be able to be considered a microdwarf. This requires a different approach to pruning than your typical garden tomato.
(As with all pruning, be sure to use clean, preferably sterilized, sharp cutting implements. I use embroidery scissors, as they get into tight spaces better than anything else I've found. I keep a set specifically for plant pruning, as using them for general purposes can leave the blades with nicks and dull spots.)
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| Newly forming sucker |
In indeterminate varieties, it is important to remove suckers, the side branches that form in the crux of a leaf and the main stem. Because of the nature of indeterminates, suckers will compete with the main stem, in essence becoming a 'new' main stem. This will result in more fruits, but all the fruit produced will be smaller. Also, eventually the plant, allowed to grow suckers at will, can become a truly massive monster bush of vines. For the sake of keeping a home garden tidy, and to get nice big fruits, pruning most or all suckers is important.
However, for determinate varieties, like all the varieties AeroGarden offers and most or all the other microdwarf varieties, suckers are a good thing. In determinate varieties, the number of fruit will not affect the size of the fruits; if there are more flowers than the plant can support, it will just shed the excess flowers. Additionally, being determinate - meaning it reaches a certain size and maintains roughly that size - the branches will only reach a certain size, and they will all produce fruit. Meaning in determinate varieties, removing branches just means you are reducing the size of your eventual harvest.
The other main difference between determinate and indeterminate tomatoes, is where the flower/fruit clusters form. On indeterminates, they grow all along the stems. However, in determinates, though you will get some clusters on the main stem, most of them form at the tips of the side branches. Thus, if you remove the suckers, you're also removing the majority of potential fruit.
This brings us, then, to some more specifics.
Because our gardens are small and indoors with not much airflow, making sure there is enough space to maximize what airflow there is can be very important to minimize risk of disease, particularly fungal infections. Because of this, I always remove the first leaf-and-sucker pairs closest to the deck (two of each, one on either side of the plant) once there are 4-5 more leaf pairs (about 6 weeks, usually), so that it doesn't rob the plant of its primary photosynthesis ability. This results in an empty space around the bases of the plants. I will remove any 'new' volunteer leaves that reach the deck, but leave all other suckers.
The next thing I do, in some cases, is controversial, and really entirely optional. Some microdwarf varieties (Heirloom Cherries, Golden Harvest, and Mighty Mini from AG are all of this type) put out the first flower branch extremely early, sometimes with only 2 or 3 mature leaf branch pairs. In these cases, I remove the first flower cluster, to allow the plants to mature a little bit more before it starts diverting energy to supporting fruit. I have actually tried before with a pair of the Heirloom Cherries, grown under the exact same conditions in the same AeroGarden - I removed the first flower branch from one, and let the other go ahead and flower. The first ripe tomato I got from the pair was actually from the one I removed the first flower branch (though the one I let grow was only a day or two behind). The amount of growth over that week or so before the next flower branch formed, allowed the plant to produce and ripen the first tomatoes significantly faster. It was also about 1/4 larger than its sibling, an advantage that remained for the span of their lives.
In some garden+variety combinations (such as growing Heirloom Cherries in a Harvest or Mega Cherries in a Bounty), the plant will eventually get taller than the garden. In order to prevent this, you have to do something called 'topping' - cut off the growing tip so that it quits growing taller and instead grows wider.
The AeroGarden instructions call for topping after 5 leaf pairs. This is a very 'no fuss' point to cut it. However, with so many more varieties in both tomatoes and gardens (these guidelines were from back when it was only Heirloom Cherries in the equivalent of a Harvest), approaching it this way is much too simplified, in my opinion. I rather wait until the specific garden's light is at full extension, then cut the tip off about 4 (for 12" tall gardens) or 6 (for 24" gardens) inches below the lights. This gives the stem a little space to expand as the plant matures, but should be sufficient to keep them within the limits of the height.
The final consideration, is the foliage. This is perhaps the most controversial part, and everyone has their opinions on 'the ideal'. Two things are relatively undeniable, though: the plant needs leaves to power itself via photosynthesis, but you can remove a fair bit of the foliage without hurting it.
Any leaf that isn't in full or close to full light, will end up using energy and nutrients (sugars) from the plant, rather than creating it through photosynthesis. Because (theoretically) there is no foliage loss due to pests or disease or water supply problems, our indoor tomatoes end up with "too much" foliage. Some people just remove leaves from the bottom up as they get shaded by higher foliage, but I dislike the 'umbrella' shape this produces, so I am as likely to remove the leaf that is doing the shading as the one that has become shaded, leaving me with a more sparsely leaved plant, but with leaves up and down the length of the plant. (This also includes leaves that grow far out from the effective cone of light from your light source.)
Note: this preference is based on the types of tomatoes I normally grow, which tend to be fairly upright in growth, like AG's Mega Cherry. If you have one of the micro-minis that tend to be a solid mass of plant that grows in a low, wide mound, like AG Mighty Minis, you'll be better off going in and removing all the inner leaves while leaving the upper layer intact. The tomatoes don't need the light (see below), the leaves do.
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| A single tomato leaf |
You can get even more specific; there is some evidence that the leaf branch directly opposite a flower cluster on the stem is 'assigned' to produce sugars for that specific flower (and thus fruit) cluster, and some have even claimed that each lobe of the leaf may be connected to a specific fruit.
But ultimately, as long as you remove leaves that are taking sugars instead of producing them, but leave enough to feed the growing fruit, which specific leaves you take doesn't make a great deal of difference in my experience.
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| The Tomato Forest, pre-pruning |
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| After pruning, nicely behaved tomato plants |
One final note: There is some belief that the fruit needs to be exposed to the light. In most cases, this is not true. There are a few varieties (usually referred to as anthocyanin varieties), that the fruits need direct light exposure in order to develop their color, such as the deep purple Indigo Rose, but even without the light exposure they will produce perfectly tasty tomatoes, just not the distinctive deep purple color. And with the vast majority of tomatoes, getting light on the fruits specifically is really not a consideration.
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