Subject: Watering or foliar spray more effective?

Date: August 1, 1997

Dear SWF:

I have a rather large vegetable garden, some perennial shrubs and some special houseplants.  Are your liquid products intended to use while watering the plants or should they be sprayed on the plants?  Which method is better for the plant, watering or spraying the foliage?  My neighbor said it didn’t matter as long as the plant got the nutrients.

Sam B.

This is a very common question.  To water, or to spray!  The technical answer is that a foliar feeding of nutrients is far more effective than watering the roots.  During the 1980’s, the people at National Air Space Ad (NASA) began experimenting with growing plants.  This was in conjunction with their program to grow plants in space.  Their experiments showed conclusively that the foliar feeding of nutrients, or fertilizers, was 900% more effective than watering the roots.  This also makes logical sense if you think about the nutrient cycles of most plants.  Much of the work in the plants are done in the leaves.  The roots provide a source and a conduit to get nutrients to the leaves where they will ultimately be utilized.  Putting the nutrients on the leaf structure bypasses the transportation issues with getting from the roots to the leaves.  Often, in a weakened or unhealthy plant, the ability to transport nutrients is one of the first casualties.

Why do you grow tomatoes?  You know that having the tomato available in your backyard is far better than a tomato grown somewhere in South America that has to get picked and sent to the packing house, where it is packed and shipped to a distributor in California, and then has to get shipped to your grocery store’s distribution center, shipped to your local store and eventually finds its place on the shelf.  It is far more effective, given the choice, to have that tomato grown and available outside your kitchen, where it can be picked and sliced and enjoyed the same day.

We all buy tomatoes from the grocery store in the winter.  They are red and often actually have some taste.  They cut up fine and work well in your salad and provide some portion of the nutrients found in your backyard tomato.  And so is the case with watering your plants.  Your neighbor is partially correct.  It is not wrong to water your plants with fertilizer, it is just better if you can do a foliar feed.  All things being equal and given the choice, the foliar feeding would be more effective.  Because of the NASA experiments, I do not expect you to see the 900% difference.  Obviously it is easier to spray your gardens than it is your houseplants.  And the houseplants love the organic seaweed products.

Many commercial growers are not set up to do foliar spraying.  Their systems utilize drip irrigation.  They continue to use seaweed products, which never touch the foliage, and continue to get excellent results.   When I spray my gardens and outside plants, I use both methods.  I overspray the leaves, topside and bottom,   allowing the runoff to drip around the plant which results in watering the plant.  On the roses, I might even spend a few minutes watering the actual base of the plant.  I spray everything in the yard, plants, grass, and deck.  Then I start over and do the whole thing again, spraying and overspraying the leaves of the plants.  This is what works for me.  If you do foliar spraying, the use of a surfactant will help.  One of the earlier questions asks about surfactants, and their use.  Just like the doses and frequency of application, you should experiment and come up with a system that works for you, knowing that any application of seaweed will be a boost for your plant.


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