Why is Media pH and EC Important in Plant Nutrition?

Springtime doesn't just bring new growth. It also brings calls from growers who are worried because their plants aren't doing well. They're dealing with stunted growth and yellowing leaves. At Voeks Inc, we find the majority of their problems come from two things: the media pH and/or media electrical conductivity (EC) values are off.

To have healthy vibrant plants, you must monitor media pH consistently. This pH shows how much nutrients are available to the plants. Levels that are too high from fertilizers can lead to overgrowth, runoff and nutrient toxicity. On the other hand, levels that are too low have other problems like nutrient deficiencies and weak plants that can't defend themselves against pests.

When the media pH is within the acceptable range, you'll have controlled growth and healthy plants.

Media EC shows the electrical conductivity of the plant. If there's too little EC, the plant will run out of energy. And if there is too much EC, there can be too much growth, plus the roots of the plants can burn.

So, it's vital that you are continually measuring media EC. Otherwise, you're just waiting until the plants show symptoms and that can be too late.

What Four Factors Affect Media pH?

When you know what elements affect the pH in peat-based media, you can have more control. They are:

water alkalinity level
amount of lime
type of fertilizer
plant root condition

Water Alkalinity: Because water is the most applied substance to any plant, the most critical factor isn't the pH, it's the alkalinity level of the water. Similar to adding lime to the media, watering increases the pH in the media. Optimum levels of alkalinity for plugs are 60 to 80 ppm. But, for larger containers and bedding plants 80 - 120 ppm is better.

Make sure when you use any type of acid injections, to test the alkalinity levels of the water every week along with the pH. Take a look at your injectors too and make sure they stay in top condition. Along with those weekly tasks, make yourself a reminder to have your water tested by a reputable laboratory every six months.

Lime Amounts: When peat-based media has a very low pH - add lime. The ideal growing range is 5.5 to 6.5. Adding the correct amount of lime adjusts pH. Overall, crops do not do well at lower pH ranges of 5.0 to 5.2.

Three types of lime you can use are calcitic, hydrated, or dolomitic.

Calcitic does an excellent job of nutreulzing soil acidity. Compared to hydrated lime, it lasts longer and reacts slower.
Hydrated lime is useful if you need something that responds quickly, but the downside is it doesn't last very long.
Dolomitic lime comes from deposits of calcium carbonate combined with magnesium, so it has the added benefit of the plant nutrient magnesium.

How quickly the pH will increase depends on the lime's particle size and amount applied. Lime activation will increase with water frequency.

Fertilizer Type: All fertilizer elements have the effect of either lowering or raising growing medium pH. This is especially true for nitrogen.

Phosphorus and ammoniacal nitrogen have an acidic reaction. These types of fertilizers bring on the soft growth of leaves and shoots quickly.
Nitrogen and calcium can increase the media pH, plus these elements also promote more toned shoot growth and healthier root growth.

No matter what fertilizer you choose, keep a close watch on the pH range and how your plants are doing. Adjust accordingly.

Root Condition: Did you know that plant roots can affect the pH media?

Vinca plants can suffer from micronutrient deficiency because of increased pH.
And geraniums have the problem of lower leaves getting micronutrient toxicities caused by lower media pH.
When root systems are older, the pH can change, so it's wise to continue testing.

What Affects Media EC or Soluble Salts?

It is vital to regularly test media EC - electrical conductivity to adjust your fertilizer programs and monitor soluble salts. This applies to high tunnel or greenhouse plants grown in soil such as ground beds or raised beds or grown in soilless media in containers.

Some of the main things that can affect EC are:

Quality of water
Starter fertilizer charge
Fertilizer rate and type
Media components
Techniques used for watering
Overall environment
The age of plant roots

The quality of the water is the most critical place to start. Conductivity should be under 0.75 µmhos. Monitor EC levels after using any fertilizers especially liquid ones. For example, if the water is 1.0 µmhos or more, electrical conductivity will be even higher with the addition of fertilizers.

If you're using a commercial mix, these have a starter charge in them. This charge aids initial growth during the first week after transplanting or sowing. So this means that when you measure the EC initially from the bag, you're really measuring the starter charge along with the gypsum or lime.

The combination of what's in the media determines the CEC or cation exchange capacity. CEC measures how many cations can be retained on surfaces of soil particles. It's really measuring how well the media hangs onto nutrients.

Fertilizers are composed of soluble salts.

So, while the crops are growing media EC is determined by:

which fertilizer you choose
how much ppm you apply
how often you use it
watering technique

Regular leaching is essential. Otherwise, salts will be built up near the bottom of the container. This will damage the roots when they enter that area.

How you water the crop will influence EC levels. If you do not leach on a regular basis, salts will build-up towards the bottom of the container and cause damage to roots when they enter that area.

And, when it comes to older roots, soluble salts don't have as big of an effect so there can be less root burn and rot.

The Importance of Weekly EC and Media pH Testing

At Voeks, Inc. we advise all the growers we work with that it's a best practice for them to do their own media pH and EC testing weekly. This should be done on all of the main crops. Doing these tests yourself will save a lot of money. Staying on top of this testing helps prevent any big unforeseen problems from creeping up. Should issues arrive, or if you want to change something significant like your fertilizer program, go ahead and use a reputable testing lab for a complete tissue and media analysis.

If you're using a commercial mix, take a sample right out of the bag. If you have your own custom mix take the sample from the hopper before sowing or planting. To get an accurate reading of the lime's effect on the media - after you water the trays or flats for a week or two - take a sample. For this test - during those few weeks just use water no feed. It will give you a good gauge of how the lime will affect your media pH.

After these initial tests, test the principal crops weekly to avoid any future problems. If issues arise with other crops, go ahead and test those.

It's best to have one person on your team do the testing at the same time each week with the same methods. This way you're not entering in any unknowns. Here are the two most used methods:

SME Method - saturated media extract is used by most commercial labs and the recommended way for soilless greenhouse media. The test is done by making a paste with soil and water. Next, the liquid is then separated out so the pH, soluble salts and nutrients an by analyzed. This type of test is for larger growers who can afford a lab and tech trained personnel.

2:1 Extraction - If you don't have a big operation with an onsite lab but want to do occasional testing, this is the way to go. 2:1 extraction is a favorite method to test pH and soluble salts. Take a sample of air-dried soil, add water, and mix together. Use 2 parts soil and one part water. Next, separate the liquid out, by pouring it through a filter. You can use a regular coffee filter. Now, test the fluid.

Next, graph your pH and EC results so you can see what's happening from week to week.

Overall, is the media pH decreasing or increasing?
Is the EC going up or is it changing all over the place?

Make sure you don't over-react to one measurement. It's normal for ED levels to fluctuate quite a bit depending on when you took the sample. Two to four hours after feeding, EC will be higher vs. one day after feeding. That's why consistency in the timing of the tests is vital.

Choosing the right measurement equipment depends on your budget. For only about $50 you can pick up a pocket pH and EC meter. They're not perfect and won't last forever but, they are affordable.

If you have a larger budget, more accurate meters can go up to $1000+. No matter what you choose, make sure you calibrate your meter weekly before you use it.

If you're not sure what type of testing equipment you should use, give us a call, and we can give you some suggestions.

How You Can Correct EC and Media pH Problems

Testing weekly will keep you ahead of the game and most problems. But you can still have some issues creep up. Here are some common ones:

High media pH - younger leaves have yellowing or lateral branching and tip abortion. Yellow leaves are most likely from a deficiency of iron, and lack of boron may be the cause of the tip abortion. Both of these problems come from high media pH. Here are ways to fix these problems:

If you're using acid injection already add more acid. For one week, either bring the water pH down to 3.0 or the alkalinity to 0.

You can also use an acid fertilizer one or two times, (21-7-7 at approx 200-250 ppm). Watch out and control too much growth with this method.

You can create an iron sulfate drench of one to two pounds per 100 gallons. The solution should have a bluish color and be dissolved. After the drenching, be sure to rinse off your plants.

Acid injection does a good job controlling alkalinity in the long run. Make sure you monitor your mix for lime amounts.

Low media pH - lower leaves have stippling, marginal burn or necrotic spots. The other thing that can result in is stunted growth and overall yellowing. Micronutrient toxicity with zinc, copper, manganese, and iron cause lower leaf problems. Too little calcium results in stubbing root tips, significant stunting, and tip abortion. Here's how to fix low media pH:

If you're using acid injection, turn the acid off. This will raise alkalinity and media pH.

Use a fertilizer that's a 15 -0-15 or 13-2-13 once or twice (200 - 250 ppm). What's nice about these fertilizers is you won't have to worry about too much top growth.

Make a lime drench of 4 quarts to every 100 gallons along with getting enough volume through the pots. Avoid any build up on the leaves by rinsing the plants with clean water afterward.

Make a potassium bicarbonate drench at 2 pounds per every 100 gallons. And just like the lime drench get enough through the pots. Afterward, make sure to rinse the plants. In a few days, add a fertilizer with some calcium.

Adding lime or readjusting the acid injection can get alkalinity into a good level on a long-term basis.

Problems with high media - a few ways to know if you have a problem is if there's root tip damage or increased root rot. Along with that be suspect if you have too much top growth.

Avoid high EC levels if you're a dry grower. If you let the plants dry down too far, you'll find ED levels building up three to four times near the roots. Some crops that commonly have high EC levels are

penta
impatiens
vinca
pansy
primula

Here are some ways to correct EC issues:

You'll want to obtain and 10% to 20% run through so make sure you water the container thoroughly. Don't water lightly, this is important when you're feeding, or the water has high EC levels.
Until the roots are more established and developed, use lower levels of any fertilizers.
If your temperatures are under 60° F, don't use fertilizers with high ammoniacal and nitrogen because it causes toxicity.
Reduce CED by adding some perlite into your mix. This will also improve drying and air porosity.
Improve the water you're using, change to reverse osmosis, rainwater or even city water if it's better than what you're already using.
Test regularly by using EC and pH meters. This will give you more control, so you're not just coping with problems after they arise.