Tuesday, March 31, 2015

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.

Tuesday, December 30, 2014

Happy New Year, Mr. Freeze!

It took awhile, but several hours of continuous freezing temperatures are finally coming to Sacramento's 2014-2015 wintertime experience...on New Year's morning. The National Weather Service is forecasting a freeze watch for a wide swath of Northern California from New Year's Eve through January 2. Their prediction includes temperatures falling into the mid to upper 20's for eight or more hours during the night and early morning hours. "A FREEZE WATCH MEANS SUB-FREEZING TEMPERATURES ARE POSSIBLE. THESE CONDITIONS COULD KILL CROPS AND OTHER SENSITIVE VEGETATION," warns the National Weather Service. 

Further down the Central Valley, the Fresno and Bakersfield areas - prime citrus growing regions - are facing even more dire predictions of extended cold this week with temperatures predicted to dip to 21 degrees Thursday and Friday mornings. That's the classic definition of a hard freeze,  deadly to plants, livestock, pets and water pipes.
Freeze Protection for Lemon Tree
 
Frozen Hosta
















 

 

  Many of us learned to take hard freeze warnings seriously in 1990, when consecutive low morning temperatures of 22, 18, 21 and 23 in Sacramento descended upon us during the period of December 21-24. Temperatures did not get above 25 degrees in parts of the San Joaquin Valley for three to five days and all time record low temperatures were set at Sacramento, Stockton, and Bakersfield. Many records were set for duration of freezing temperatures. The agricultural industry was devastated as acres of trees, not just fruit, were destroyed. Thirty-three counties were disaster-declared.

Homeowners back then learned which plants don't like it cold (hibiscus, geraniums and other plants popular in the Bay Area and Southern California); and, which plants were the hardy survivors (another reason the oleander was chosen for the Highway 99 median strip).
The National Weather Service has a nifty Tabular Forecast chart link within their "Additional Forecasts and Information" list at the bottom of their local forecast page. This tabular chart predicts the temperature, hour by hour, for the selected location, for the next six days. This is probably more useful for predicting the duration of freezing temperatures, rather than the actual temperatures themselves. When those durations exceed four hours at temperatures of 28 degrees or less, that's when plant damage can become fatal to sensitive plants. Remember to pinpoint your own location when using the local forecast page link by using the Google map embedded on that page to find your location.
Here's a last minute checklist for your home and garden if the TV weather people (or panicky bloggers) tell you upcoming morning low temperatures will be in the mid-20's:
 
• If it hasn't rained, water plants thoroughly, especially container plants.

 
• If possible, move sensitive container plants next to a south or west facing wall.

 
• Cover citrus and other sensitive plants with burlap, row cover fabric or sheets (be sure to keep the sheets dry). Tent plastic sheets on supports over the plants; don't let plastic touch plant leaves. A light bulb placed in such a plant can offer a few degrees of protection. For best protection, sheets should reach all the way to the ground around citrus trees and other freeze-susceptible plants.

 
• If using an anti-transpirant polymer coating material such as Wilt-Pruf or Cloud Cover, apply at the warmest time of the day, or at least six hours before an expected frost. Read and follow all label directions. If using these products, thoroughly water the plant before applying. In my opinion, use these coatings only as a last resort. Watering plants, moving plants or covering/adding heat to sensitive plants is a more effective strategy.

 
• Disconnect hoses and drip lines, removing end caps. Lay out straight, off the driveway and out of the path of vehicles. If possible, turn off any exterior water lines at the main; or, thoroughly wrap any exposed pipes and faucets.

  • To prevent broken grass blades, don't walk on a frozen lawn.
 
• Remove the lowest sprinkler head on each line for drainage.



Protect exposed pipes around wells and pumps
  







  • To prevent frozen attic pipes, let lukewarm water trickle out of the indoor faucet farthest from the inlet. Also, let faucets with pipes running along an outer, north facing wall trickle during the night.  
 
 
• Open cabinet doors to get more heat to the pipes. Close the garage door if water pipes pass through the garage.
 
• Setting your thermostat nightly at 55 can add needed heat to the attic pipes.

 
• If leaving the house for a vacation during an expected freeze, turn off the water to the house, and open up the faucet farthest from the inlet. Be sure to turn off your water heater.

  • Cover unprotected faucets and pipes, including any spa or pool equipment.
 
• To prevent cracking tile, run your pool and spa equipment during the freezing hours. 

 
• Don't forget about your pets during a prolonged freeze. Bring them indoors at night. Move or replace their drinking water. Break up any frozen water in bird baths. 


 




• Cover the worm bin, too! Or, move it indoors.