Pruning Tomatoes: Don't You Have Anything Better To Do?

Once again, two tomato care questions have reappeared here: "Should I prune off  (snip off, pinch out) the first tomato flowers that appear, in order to get more tomatoes later?" And, "Do I need to prune my tomato plants?"

Those early tomato flowers, especially if the weather doesn’t cooperate, will fall all by themselves, thank you. Your assistance is not needed. And if you want to prune your tomato plant, you better have a damn good reason.

Flower drop and tomato fruit set failure can happen in May and June for a number of reasons, including night temperatures below 55; daytime temperatures above 90; excess nitrogen fertilizer, too much shade, too much smog, plants set out too early in spring, or planting the wrong variety for your area (Beefsteaks and San Francisco is not a match made in heaven).

However, by removing those flowers once they are in a situation where they can be pollinated successfully, what is accomplished by removing those flowers? FEWER TOMATOES! And, unless you are trying to stop production, it would be counterproductive to your ultimate goal: shoving that beautiful red orb into the face of your non-gardening neighbor in July, singing, “Nyah, nyah, nyah!”

Wow, where did this fallacy begin? One caller to the radio show offered a clue when he prefaced that question with, “Last night, the local TV Weatherman said…”

Bad move, taking gardening advice from a person who guesses for a living.

Still, that piece of  poor advice must have some historic legs to it. And sure enough, there are many people at Internet gardening forums who are passing on this wrong-headed notion. And as far as I can tell, it’s the result of one gardener reading a piece of university-based research on tomato pruning, and mangling the retelling of that research.

For example, Texas A and M University offers these tips for tomatoes:

"Greenhouse/Hydroponic Tomato Culture (winter)
Single crop rotation-seeded in July or by early August.  Transplants set in greenhouse within 10 to 30 days of seeding.  Harvest begins from 85 to 100 days following date of seeding and continues into June or early July.  Cessation of pollination is six weeks before  termination of the crop.  Growing point is allowed to grow for at least five to seven leaves  above last fruit truss to help prevent sunburned fruit.  Remove flower buds above last fruit truss to assure no additional fruit set."

Gardener A reads this, and then retells the story to Gardener B, omitting the fact that these were WINTER tomatoes grown in a GREENHOUSE, HYDROPONICALLY. Gardener B then tells Gardener C: “Pruning tomato flower buds is recommended by Texas A and M.” Gardener C then goes online and writes: “Remove flower buds on tomato plants to increase the number of tomatoes.”

Or something like that. And another digital gardening virus is born.

PRUNE YOUR TOMATO PLANTS? WHY?

Cornell University says hacking back your tomato plants is not necessary:

“…you can grow perfectly fine fruit without pruning your plants. But if you want to prune, here are a few guidelines. For determinate types, there is no need to prune at all. For indeterminate types, allow one, two, or three suckers to grow from the base of the plant. Each of these will become a main stem with lots of flowers and fruit. Prune off all the others suckers and provide the plants with strong support. 

Research has shown that the best time to remove suckers is when they are about 3 to 4 inches long. For the semi-determinate types, limit your pruning. When the plant is 8 - 10 inches high, look carefully and observe the first flower cluster on the stem. Remove all the suckers below the flower cluster except for the one immediately below the cluster. You may have to go back and give these a second pruning 7 to 10 days later. Remove no more than that or you run the risk of pruning too much. The amount of pruning among these varieties to produce optimum yields varies. Some varieties would do better if you left 2 suckers below the flower cluster. Experiment and see which works best for the variety you are growing.”

The book, “Ortho’s All About Tomatoes”, puts it more succinctly, quoting the late Dr. Phillip Minges of Cornell: “Tomato yields per plant may be lowered by pruning. Removing the leaves or shoots does not conserve food for the crop, it tends to reduce the total food supply…use training methods that require little pruning.”

When and how should you prune tomatoes?
Very little, only when necessary, to keep the plants within bounds. If you grow your tomatoes in cages (recommended), you would only need to remove those branches that escape and are threatening to wrap itself around a nearby pepper plant.

If you grow your tomatoes using stakes for support, you may need to reach for your garden pruners, according to the University of California:
“Staked tomato plants usually require pruning to a few main stems. At the junction of each leaf and the first main stem, a new shoot will develop. Choose one to three of these shoots, normally at the first and second leaf-stem junction, for the additional main stems. Once a week, pinch off most of the other shoots, called suckers, with your fingers, to keep the plants from becoming to large for their support.”

And, it should be pointed out, that if you follow those pruning guidelines for staked tomatoes, you are sacrificing about 25% of your eventual tomato crop.
 That is yet another good argument to cage, not stake your tomatoes.

Cages can be made from sheets or rolls of concrete reinforcement wire with a six inch mesh (the six inch opening makes it easier to reach those tomatoes). The sheets are usually 42” by 84”. Snip off the vertical bars on one of the 42” ends, bend it into a circle, attach the horizontal arms from the snipped end around the other  42” side and you have a tomato cage that’s 42” tall and about 27” in diameter. And it will last for decades. Want a bigger cage? Turn the sheet sideways, snip one of the long ends, bend it into a circle, and you have a cage that’s 84 inches tall and about a foot wide. But I would only do that if I am trying to grow tomatoes as per the instructions of a square foot garden.

And if you need another reason NOT to prune your tomato plants, there's this:
Sunscald (sunburn) of tomatoes. The fruit turns light brown and leathery on the side exposed to the sun. The solution? Don't prune the leaf cover from the plant!

 
A final hint when searching for garden answers on the Internet. Be leery of advice from gardening forums, unless that advice is linked to a study or research that you can also access. When using a search engine, include the words to identify a prominent agricultural school where the advice is reviewed by multiple parties before publication: UC (University of California), WSU (Washington State), Cornell, TAMU (Texas and M), etc.
For example Googling the phrase “tomato worm UC” will lead you to the University of California Integrated Pest Management website first. If you were to just enter the words, “tomato worm”, well…good luck.

Foliar Feeding: The Pros and Cons

  You know how it is: you hear something enough, you believe it's true. Look on the side of any box of water soluble fertilizer, or any organic gardening guide, and there will be instructions on foliar feeding: spraying a water soluble fertilizer onto the leaves of a plant, as an alternative source of nutrition for the plant.

      Awhile back on the radio show, a tempest in a teapot developed when Milo Shammas, the President of the Dr. Earth line of organic products, mentioned that the best way to apply a foliar fertilizer, which he endorses, is in as fine a spray as possible. In his corner, Rodale's Encyclopedia of Organic Gardening, which states: "Plants can absorb liquid fertilizers through both their roots and through their leaf pores. Foliar feeding can supply nutrients when they are lacking or unavailable in the soil, or when roots are stressed. It is especially effective for giving fast growing plants like vegetables an extra boost during the growing season...Any sprayer or mister will work, from hand trigger units to knapsack sprayers. Set your sprayer to emit as fine a spray as possible."

      Disagreeing with the "fine spray" approach is another organic advocate and frequent guest of the radio shows, Steve Zien of the Sacramento area-based organic consulting service, Living Resources Company. 
     Zien says, "Some time ago I read a few studies that indicated that most of that (spraying with a fine spray) was not necessary. The studies used radio isotopes to follow the nutrients in the foliar fertilizer. They found that it got into the plant even when the water droplets were large. Another study indicated that even with the best spray equipment making the smallest water droplets possible with today's technology, the water droplets were still too large to physically enter the plant. They concluded that water droplet size is not important when foliar feeding. Other studies have shown that foliar fertilizer can even be absorbed by branches and tree trunks.  These two facts indicate that where you spray is also not critical.  Numerous studies have shown that foliar feeding is much more efficient at getting the nutrients absorbed and to the entire plant and more rapidly as well. 
     I think all the studies emphasize that even with all the benefits of foliar feeding, it cannot be considered a substitute for proper soil nutrition, and I fully agree with that. You need to feed the soil foodweb for healthy, pest resistant plants.I no longer worry about where I apply the foliar fertilizer. I try to apply it to as many plant surfaces as possible but do not worry about paying attention to the undersides of the leaves."

     Throwing cold water on both those practices are a couple of college educators, Deborah Flower of the Horticulture Department of American River College in Sacramento; and, Linda Chalker-Scott of the Horticulture Department at Washington State University and author of the award-winning book, "The Informed Gardener", who says this about foliar feeding: 
     "The existing research does not justify foliar fertilization of landscape plants as a general method of mineral nutrition. It can be useful for diagnosing deficiencies; for instance, spraying leaves with iron chelate can help determine if interveinal chlorosis is from iron deficiency. It would obviously have a benefit for those landowners with landscape fruit trees that perpetually have flower or fruit disorders associated with micronutrient deficiencies. Applying fertilizers to leaves (or the soil) without regard to actual mineral needs wastes time and money, can injure plant roots and soil organisms, and contributes to the increasing problem of environmental pollution. The bottom line:
• Tree and shrub species differ dramatically in their ability to absorb foliar fertilizers.
• Proper plant selection relative to soil type is crucial to appropriate mineral nutrition.
• Foliar spraying is best accomplished on overcast, cool days to reduce leaf burn.
• In landscape plants, foliar spraying can test for nutrient deficiencies, but not solve them.
• Micronutrients are the only minerals that are effectively applied through foliar application.
• Foliar application will not alleviate mineral deficiencies in roots or subsequent crown growth.
• Foliar spraying is only a temporary solution to the larger problem of soil nutrient availability.
• Minerals (especially micronutrients) applied in amounts that exceed a plant’s needs can injure or kill the plant and contribute to environmental pollution.
• Any benefit from foliar spraying of landscape trees and shrubs is minor considering the cost and labor required."

     Chiming in is Deborah Flower of American River College: "I have been reading 'Plant Physiology' by Taiz and Zeiger, and 'Mineral Nutrition of Higher Plants' by Horst Marschner.  The latter discusses foliar feeding in chapter 4.  It says: there are small pores in the cuticle through which minerals can enter the plant.  These pores are in highest density near guard cells around stomata and at base of trichomes (hairs, scales, etc.).  They are tiny and lined with negative charges.  So, only very small (less than one nanometer in diameter) cations and uncharged molecules will enter these openings.
It says leaves do absorb ions, but (pages 123-125):
Rate of uptake is VERY low.
Rate of uptake varies between species and growing conditions.  Plants with thicker cuticle (due to species or growing conditions) absorb less.
Older leaves have lowest rate of uptake due to leaky plant cells that fill intercellular spaces, which is where ions travel in the leaf.
A very high concentration of ions is needed outside the leaf to get any into the leaf.
The supply of nutrients in the leaf from foliar feeding is temporary.
There is limited movement of nutrients from leaves to other plant parts.
Urea can enter leaves through these openings (ammonia and nitrate cannot), because it is an uncharged particle, but can cause damage in the leaf, due to nutrient imbalance in the leaf once it is absorbed.
Surfactants should be used with all foliar feeding to increase surface spread of spray.

      So, my opinion is that yes, plants do absorb nutrients through their leaves (neither book mentioned absorbtion through branches or trunks) but the amount is very small, nutrients do not travel far from point of entry, and there is lots of nutrient run-off during the process, which can lead to pollution.  Therefore, foliar feeding is not effective as the primary source of nutrients for plants. I disagree that foliar feeding gets nutrients to all parts of the plant. There is lots of evidence that fertilizer that gets into the leaf migrates little to other parts of the plant. It stays in the leaf or travels to a strong sink like a fruit.  Foliar feeding can correct micro-nutrient deficiencies in leaves and some fruit, but until the nutrition is balanced in the root zone, the symptom will continue to appear in new plant parts. Many of my students seem to believe foliar feeding is better for the plant than nutrient absorption by roots, and that concerns me.  Foliar feeding can be used to correct some nutritional problems, primarily in production situations, but should not be relied on as the primary source of nutrients for the plant. If people are foliar feeding I believe most of the nutrients being absorbed by the plant are entering the roots, probably after running off the plant onto the soil."


  Milo Shammas, of Dr. Earth, responds: "Fred, all very true and I agree with her, I do not recommend foliar feeding as the primary source of nutrients. Whatever runs off the foliage will ultimately be absorbed by the root system. Nothing can replace ion absorption through the root system.
 Foliar feeding as a supplement? Yes
Is it effective? Yes
Would I depend on it solely? No
Is there harm in using it? No
Do younger leaves absorb it better? Yes
 I own and manage 45 acres of organic walnuts and I personally spray my ranch with Dr. Earth liquid solution twice a year,  I do spend the money on it, I have conducted the efficacy and I know it works, I do believe in it, I do endorse it, I do not depend on it."

    After standing back, listening to all this, I have come to the conclusion: although foliar feeding may have minimal value, it does have a bigger, positive effect: washing off bad bugs from the leaves. Of course, a spray of water can accomplish the same thing.