For; Pacific Coast Nurseryman

High Soluble Salts and Water Stressed Plants

A Big Problem in the Interiorscape

by

Julie P. Newman

Scorched leaf tips and margins are a common sight in the

interiorscape. Everywhere you go, you'll find beautiful plants marred by

brown crispy ends. This problem is more common than root rot diseases,

though it's often confused with maladies caused by soil pathogens. It is

even more prevalent than mealybugs and spider mites. What our plants are

suffering from is a widespread epidemic caused by too much salt and not

enough water. Toxic substances such as fluorides and boron are also to

blame. Looking at the interior landscape industry on the West Coast today,

this may be the biggest cultural problem we face.

Interiorscapers often inherit fluoride and boron toxicities from the

grower. Soluble salts, on the other hand, may become a problem, due to

the use of poor quality water in maintenance programs. In many areas of

California, interiorscapers must contend with salty water - water

containing an abundance of soluble minerals. However, even in areas where

water is relatively pure, such as in Seattle, soluble salts in the growing

medium may still wreak havoc for interiorscapers, due to excessive

fertilizer applications and water stress.

How water stress affects plants

What is happening is that when plants are irrigated and/or fertilized

they are literally bathed in salt water. As water evaporates from the

growing medium or is used by the plant, the salts left behind in the medium

become more concentrated. Plants may not get watered again until the medium

is very dry because of maintenance schedules. During this time the salts

may accumulate to levels that are injurious to plants.

The high salt levels created by low moisture in the growing medium

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indirectly injure plants by inhibiting water absorption by the roots. In

addition, water may actually leave the roots and move back into the medium

in response to a salt gradient. Plants wilt, the breathing pores (stomata)

close, and photosynthesis shuts down.

At the Interior Plantscape Workshop of the 1986 Ohio Florist Short

Course in July, Dr. John Peterson spoke about water studies conducted at

Ohio State University. These studies show that water stress has long

lasting effects in the interiorscape. Although wilted plants may regain

turgidity once water is replaced, their vigor is reduced. Plants that have

been water-stressed grow more slowly than unstressed plants and their

quality is not as good.

In addition, water-stressed plants are more susceptible to pest and

disease problems. For example, Dr. Richard Linquist of Ohio State

University, who also spoke at the Interior Plantscape Workshop, found that

moisture stress creates chemical changes in the plant that make it more

susceptible to spider mite infestations.

What happens in extreme cases

If salt levels become excessive, direct injury may occur and roots may

be damaged or killed. As a result, water and nutrient uptake ceases. Plants

wilt and yellowing (chlorosis) may occur. Leaf tips and margins may die,

usually beginning near the top of the plant and progressing towards the

roots.

Water quality is important

Every water source used for irrigation and to make up fertilizer

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solutions should be periodically analyzed by a reputable lab. As an

alternative plantscapers may examine tests that municipal water districts

are periodically required to make. If the water is high in soluble salts,

particularly magnesium, calcium, and sodium chlorides and carbonates,

problems in the interiorscape can be expected.

In certain situations it may be possible to switch to another water

source or to blend poor quality water with good water. Correcting poor

quality water may involve installing a water purification system such as a

reverse osmosis system. Cation exchange water softeners are unacceptable in

the interiorscape because they replace calcium and magnesium with sodium

chloride. Use of softened water may result in toxic levels of sodium and an

increase in soluble salts. In addition, sodium ions destroy aggregates so

that the structure of the medium may deteriorate.

Fertilizers can contribute to the problem

Fertilizing at an excessive rate or too frequent applications of

fertilizer can also cause problems in the interiorscape, due to soluble

salt accumulation. In most interior situations the objective is to maintain

plants rather than force them into rapid growth. Less fertilizer is

therefore needed than in a production situation.

The amount of fertilizer needed by plants is directly related to light

intensity and duration. Residual fertilizers remaining in the growing

medium from applications in the greenhouse may actually be toxic to plants

moved into a low light situation. Such plants should be thoroughly leached

before placing them into the account. In practice, however, this is rarely

done, in the client's haste to get the plants installed.

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"Perhaps the solution here," says Dr. Charles Powell of Ohio State

University, "is for a new breed of businessman to emerge. This person would

be a sort of broker that would offer acclimatized plants to the

interiorscaper."

Dr. James Knauss of W. R. Grace & Co. provided some fertilizer

guidelines for interiorscapers at the Ohio Florist Short Course (see Table

1). Under the low light conditions prevalent in many interiorscape sites,

fertilizing may only be necessary 1 to 2 times per year. He advises

interiorscapers to have their growing media periodically analyzed by a

reputable lab to determine the best fertilizer program.

Self-watering pots can help

Even with good quality water and optimal fertilizers, soluble salts

may accumulate due to excessive drying of the medium. Though the

concentration of salts may be satisfactory for plant growth when the medium

is wet, as the soil dries the concentration of salts increases.

Some interiorscapers are getting around this problem by using

controlled watering and/or self-watering pots. In these systems, water

moves up through the growing medium from the bottom. Because the medium

remains moist, the salts don't get concentrated.

According to Dr. Peterson, plants growing in these systems do not get

water-stressed, and growth, quality and longevity is enhanced. However, if

the objective is to avoid soluble salt problems, it is important not to

mulch the surface, so that salts can be pulled up by evaporation. In

addition, it may occasionally be necessary to scrape off the top of the

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growing medium to remove salts that accumulate there.

Fertilizing in self-watering pots can be tricky. "Under 200-foot

candles, don't fertilize any more than once per year," advises Dr.

Peterson. He suggests using 1/2-1/4 the recommended rates in self-watering

pots because the fertilizer stays in the pot.

Don Campbell of Interior Gardens in Santa Barbara agrees that "the

quality of plants grown in self-watering containers is definitely

superior." An additional benefit is a decrease in pesticide applications.

"We have almost no spider mite problems on our plants grown in self-

watering pots." However, he says that most people in the industry still

hand water.

The problem, says Ron Aisenbrey of New Products Development (Mono

Systems) is convincing the client that the extra cost for the containers is

worth it. "Even if you're successful, then your clients may think you're no

longer needed because you don't have to come by so much to water. They may

not understand that you're now able to spend more time in the accounts

using your horticultural expertise in pest management, pruning and

fertilizing." The solution, he surmises, may be to purchase the containers

yourself. "You'll still save money because of your reduced labor

requirements."

Other techniques to overcome salinity problems

The alternative for those that continue to use conventional hand

watering is to periodically leach. This involves applications of heavy

water to remove the salts that have accumulated. This method is only

successful if you have good drainage.

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Dr. Knauss has a trick to try in situations where inadequate drainage

or a particular growing medium prevents leaching. He suggests an

application of a sugar solution (1 to 2 lbs/10 gallons of water), applied

at 2 pints/sq. ft. of media surface. This causes a rapid explosion of

microbal growth. Microorganisms are capable of tying up a large quantity of

excess salts, thus negating the detrimental effects.

Dr. Knauss also has a solution for excessive accumulates of sodium. If

leaching is possible, the application of gypsum (calcium sulfate) to themedia surface at the rate of 5-10 Ibs./lOO sq.ft. (1 Tbs./sq.ft.) followed

by thorough irrigation will displace the sodium ions and result in their

subsequent leaching.

Know the salinity of your media

Soluble salts in water extracts of the growing medium can be easily

measured by interior plantscapers with a Solubridge. This instrument

measures electrical conductivity in milli-mhos per centimeter at 25° C.

Readings of less than 2 would indicate no salinity problem; readings of 2-A

indicate a level at which sensitive plants may be damaged. Readings much

over 4 indicate a level where most plants are likely to be detrimentally

affected.

JPN:jkr08/05/86

Julie P. Newman is Environmental Horticulture Advisor with the University

of California, Cooperative Extension, in Santa Barbara County.

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TABLE 1 INTERIOR PLANTSCAPE FERTILIZER SUGGESTIONSFOR A 24% WATER SOLUBLE FERTILIZER PRODUCT/

24% Feed Level (ppm N)

LightLevel

FeedInterval

Low^

FeederMedium

,

FeederHeavy ^Feeder

Low (100-300 FC)

1 to 2times/year 75^ 150 225

Medium (500-1,000 FC)

2 to 4

times/year 150 225 300

High (1,000-3,000 FC)

one/monthduring highlight months 150 300 375

Very High ^(3,000 -

10,000 FC)

once/monththroughoutthe year

Not

Applicable 300 375

^From;

Knauss, J. F. Making the most out of plant nutritional maintenance. Paperpresented at the Ohio Florist Short Course, Columbus, Ohio; 1986.

2 Includes such genera as Asparagus, Fittonia, Maranta, Peperomia, Pilea,Sansevieria.

2 Includes such genera as Aglaonema, Araucaria, Calathea, Chamaedorea (i.e.C. elegans), Cissus, (i.e. C. rhombifolia), Cordyline, Dizygotheca,Dieffenbachia, Dracaena, Hedera, Hoya, Nephrolepis, Spathiphyllura,Yucca.

^ Includes such genera as Aeschynauthus, Aphelandra, Brassaia, Chamaedorea(i.e. C. erumpens), Chlorophytum, Chrysaliodocarpus, Codiaeum, Dracaena(f*®' 9. marginata), Epipremnum, Ficus, Philodendron, Polyscias,Syngonium.

^ For 24-8-16 Water Soluble, 4.2 oz/lOO gal (1/4 teaspoon/gal) equals 75ppm N.

^ This light level usually occurs only in high light areas of the U.S.A.,particularly the Sunbelt areas. Use good light meter to determine footcandles (FC).