Are Your Geraniums Showing Signs of Iron or Manganese Toxicity? It May Be Due to Low pH Levels

Iron and Manganese toxicity in geranium
Zonal geraniums at a greenhouse business exhibiting iron and manganese toxicity symptoms caused by a low pH of the growing media.

Geranium growers may occasionally find that their zonal plants are exhibiting symptoms of iron and manganese toxicity. The increased prevalence of this problem in some areas can be at least partly attributed to starting with media with a low pH (4.0 to 5.3).

Michigan State University Extension experts recommend growers continuously monitor the pH and EC of crops so trends or problems can be detected early. Growers should also calibrate pH meters prior to first use during the season.

Here are some commonly asked questions when it comes to pH monitoring (courtesy of Michigan State University).

What substrate pH is recommended for zonal geraniums?

The ideal pH for growing zonal geraniums is between 6.0 and 6.5. They are the poster child of plants that readily absorb iron and thus are referred to as iron-efficient crops. In contrast, other crops such as petunia and calibrachoa are iron inefficient and require a lower substrate pH of 5.5 to 5.8 to prevent an iron nutrient deficiency.

What symptoms do you see when the pH of the substrate is too low?

• Brown speckling of leaves, especially toward the outer margin
• Leaf chlorosis or yellowing around the edges
• Upward cupping of leaves in some varieties
• Stunted growth

How can I increase media pH quickly to prevent toxicity symptoms on new growth?

Growers can increase the substrate pH by drenching with a suspended limestone (flowable lime), potassium bicarbonate, or calcium carbonate. The recommended rates will strongly depend on your initial pH. Drenching the growing media with one of these products is generally only recommended if the pH of the substrate is excessively low (less than 5.5).

If the pH is only slightly lower than recommended (5.6 to 5.9), consider changing to a more alkaline fertilizer. Growers who have highly alkaline water and normally inject acid to neutralize the bicarbonates could stop acidification to raise the pH of the media. However, these strategies can be difficult to implement when growing a wide variety of iron efficient and iron inefficient crops together.

What should I do if some geraniums have a low pH while others in the greenhouse do not?

It is recommended that growers sort out the geraniums that are exhibiting iron and manganese toxicity symptoms and have a low pH from those that are not. Because the growing media pH may have varied between bales, some growers may see that only some plants are exhibiting symptoms. Growers should apply a corrective drench only to those plants with a low pH.

Check out the complete article on the Michigan State Extension page for more tips and links to additional resources.

Topics: , ,

Leave a Reply

More From Media...
Growing Media Mixing Model

August 28, 2017

New Mixing Model Predicts Rooting Media Properties

Researchers at Wageningen University & Research have developed a mixing model that predicts the properties of a mix of constituents in any growing media ratio.

Read More
Vijay Rapaka

July 30, 2017

Oasis Grower Solutions Hosting Plant Production Webinar

The webinar, which takes place on Aug. 10, will provide information on growing media for cutting propagation and seed germination.

Read More
New Growing Media Blends

July 26, 2017

British Researchers Evaluating New Media Blends to Reduce Coir Reliance

Research in the United Kingdom has shown that coir-free growing media has the potential to work as well as coir for strawberry crops, and these research results likely apply to greenhouse production, as well.

Read More
Latest Stories
Growing Media Mixing Model

August 28, 2017

New Mixing Model Predicts Rooting Media Properties

Researchers at Wageningen University & Research have developed a mixing model that predicts the properties of a mix of constituents in any growing media ratio.

Read More
Vijay Rapaka

July 30, 2017

Oasis Grower Solutions Hosting Plant Production Webinar

The webinar, which takes place on Aug. 10, will provide information on growing media for cutting propagation and seed germination.

Read More
New Growing Media Blends

July 26, 2017

British Researchers Evaluating New Media Blends to Redu…

Research in the United Kingdom has shown that coir-free growing media has the potential to work as well as coir for strawberry crops, and these research results likely apply to greenhouse production, as well.

Read More
Iron and Manganese toxicity in geranium

June 13, 2017

Are Your Geraniums Showing Signs of Iron or Manganese T…

Zonal geraniums with low pH can exhibit iron and manganese toxicity symptoms, including marginal chlorosis, leaf speckling, and upward-cupping of the leaves, according to Michigan State University experts.

Read More
GrowTech CatEyePlug Feature

June 6, 2017

Grow-Tech Introduces New Media Plug, Joins Dümmen Orang…

Grow-Tech LLC, a designer and manufacturer of stabilized growing media products, is making waves this week with the launch of a new plug and an announcement that it is joining forces with Dümmen Orange.

Read More
rhp-substrates-root-problems-web

May 9, 2017

How to Test and Correct for Low Substrate pH in Your Gr…

If you mix your own or purchase a pre-mixed substrate, it is recommended you determine the initial pH. In too many cases, growers end up discovering low substrate pH.

Read More
pbh-peat-mix-feature

January 2, 2017

Why You Need To Know What’s In Your Growing Media…

Before you buy growing media mixes or raw materials to mix your own custom blends, here are some important factors to consider.

Read More
zenplug-with-orchid-from-grow-tech

December 25, 2016

Grow-Tech Patents Plug Designed for Tissue Culture

The ZenPlug from Grow-Tech is used for tissue culture in orchids and difficult-to-root cuttings, and is one of several products recently developed by Grow-Tech.

Read More
Various Wood Substrates

December 18, 2016

The Evolution And Revolution Of Wood Substrates

Growing media formulations are evolving as researchers fine tune blending techniques for wood component substrate alternatives to achieve reliable, consistent results.

Read More
oasis-grower-solutions

December 17, 2016

New Growing Media Technology Designed To Promote Health…

Oasis Grower Solutions recently launched several new innovations that support plant growth and health all the way to maturity.

Read More
mycoapply-from-mycorrhizal-applications-feature

December 5, 2016

New Growing Media Advancements Giving Growers More Opti…

With innovative, sustainable growing media components, growers will be able to improve plant health, achieve consistency among crops, save money, and reduce inputs, while saving space on storage.

Read More
growing-media-december-2016-feature

November 27, 2016

How The Sustainability Movement Impacts Growing Media

As consumers continue to focus on sustainability, growers need cost-effective media additives and options that produce high-quality plants, all while conserving precious natural resources and reducing the grower’s carbon footprint.

Read More
berger-forest-gold-feature

November 6, 2016

Growing Media Suppliers Are Focusing On Consistency

Here’s what three companies are doing to educate growers, while delivering products tailored to their specific needs.

Read More
Pindstrup Logo

October 6, 2016

Pindstrup Groups Open Modern Wood Fibre Plant In The Ba…

The Pindstrup Group recently opened a new wood fibre plant near Riga, Latvia, for the production of Forest Gold, a new component for growing media.

Read More
inorganic-media components

October 6, 2016

Online Learning Center Features Advice On Growing Media

This grower resource features videos and articles on how growers can most effectively promote plant health.

Read More
rhp-substrates-root-problems-web

October 5, 2016

How The Wrong Substrate Can Increase Potential For Root…

RHP, a European knowledge center for substrates and growing media, recommends using airy substrates in winter to provide more oxygen to the plant.

Read More

September 22, 2016

Peat Moss Supplies Look To Be Down In 2016

The annual harvest update from the Canadian Sphagnum Peat Moss Association calls for below-average numbers in several major production areas.

Read More
LM-Bark 1 (Lambert Peat Moss)

August 3, 2016

Learn The Basics Of Growing Media From Texas A&M Un…

The Texas A&M University AgriLife Extension website offers growers a primer on growth media, from the most common types of materials to how to prepare them.

Read More