Plant Care


An Essential Nutrient for Healthy Hibiscus

Potassium is the essential mineral for blooming in hibiscus, but another mineral, magnesium, is essential for glossy, green leaves and good growth. Interestingly enough, these two minerals actually compete in nature. The more potassium a plant needs, the more magnesium it also needs, and too much of one without balancing amounts of the other can create a deficiency. Potassium deficiency shows up in a lack of blooms, poor flower color, and weak, spindly wood. Magnesium deficiency shows up in yellow leaves, or chlorosis. By constantly giving our hibiscus large doses of potassium to keep them blooming with big colorful flowers, we can actually create a magnesium deficiency that stresses the whole plant. At the risk of sounding like science geeks, let's see if we can explain this . . .

Why Do Plants Need Magnesium?

Magnesium (Mg) is at the Center of
Every Molecule of Chlorophyll
Magnesium is one of the most essential minerals for all green parts of a plant because it is used to make chlorophyll, the green pigment in plants that turns water, air, and sunlight into food for the plant. Magnesium is the central atom that the chlorophyll molecule is made around. Without magnesium, plants just can't make chlorophyll, and without chlorophyll, plants slowly die. Look at the diagram of a chlorophyll molecule at right. It may look like confusing gibberish to you, but right in the middle you see a magnesium atom (Mg) surrounded by four nitrogen atoms (N). Everything else is just oxygen, hydrogen, and carbon, the basic atoms in air and water. Even if you understand nothing else, it's easy to see that to make chlorophyll, plants must have enough magnesium, as well as the nitrogen we give them constantly in our fertilizers.

How Do Hibiscus Become Deficient in Magnesium

Good fertilizers should contain magnesium in the right ratio for the plants they are designed for. Our HVH Special Blend Fertilizer contains the ratio of magnesium, nitrogen, potassium, phosphorus and other micronutrients that hibiscus need. If you use a good hibiscus fertilizer alone, your hibiscus should be fine. Sometimes hibiscus get into trouble when we greatly increase potassium by adding large amounts our HVH Hibiscus Booster to our plants to make them bloom more abundantly and with brighter colors. With very heavy doses of extra potassium added to our plants, they sometimes need an increase in magnesium to keep them green and glossy. Potassium and magnesium have to be in balance in order for the plant to be super healthy as well as to bloom well.

Other conditions that can cause magnesium deficiency are poor soil, very hard or alkaline water or soil, not using enough fertilizer, or not using a high quality fertilizer. High heat in late summer can exacerbate magnesium deficiency, so if you haven't seen signs of it before, you may suddenly see it during the summer and fall months.

What are the Symptoms of Magnesium Deficiency?

Symptom of Magnesium Deficiency
Young upper leaves are green and healthy.
Older lower leaves are yellow with dark green veins.
Magnesium deficiency shows up in yellow leaves, or chlorosis, like so many other hibiscus ailments! But with magnesium deficiency, the oldest leaves turn yellow between the veins. Look down low on your plants for leaves that have dark green veins with yellow or yellow and brown between the veins, sometimes with brown edges. The plant tries to send all the magnesium it has up to the tips to the new growth, so the chlorophyll in the lower leaves is broken down and disappears, leaving the strange green-veined yellow look that is the tell-tale sign of magnesium deficiency.

Using Epsom Salts to Supplement Magnesium

For many gardeners, magnesium deficiency can be cured quickly, inexpensively, and easily with epsom salts from the grocery store or drug store. We have bought "horticultural grade" epsom salts and compared them to grocery store epsom salts, and can find no difference in the results. Epsom salts are very water-soluble and can be watered into pots or the ground to supply the extra magnesium that your hibiscus need from time to time.


Epsom salts work well for hibiscus planted in the ground in areas with neutral or acidic soil, or for plant in pots where the water drains out the bottom and isn't constantly taken back up into the pot.

Hibiscus that Need Chelated Magnesium

Hibiscus grown indoors with trays under the pots, or in higher-stress lower-light conditions do better with a rapidly absorbable chelated form of magnesium. Likewise, hibiscus grown in areas with hard or alkaline water or alkaline soil will often not be able to absorb the magnesium in epsom salts before it runs out of the soil. This has been our problem with epsom salts here in Southern California where the water is very hard. The minerals in the hard water and alkaline soil compete with the epsom salts, and block the uptake of magnesium from all sources. The molecules in chelated magnesium are able to enter the plant much more easily and are absorbed very quickly into all parts of the plant, so we find it works much better in our hard-water Southern California conditions.

This is our favorite chelated magnesium product, one that we have used for years ourselves and at long last have available for our customers: Fulmag Chelated Magnesium. This magnesium is highly absorbable, instantly usable for all parts of the hibiscus plant, and gentle enough for frequent use. It contains no nitrogen or other salts that can burn your plants, and it is completely compatible with all our other products. It can be mixed right into the fertilizer of booster water with your regular nutritional program.

NOTE: If you use the HVH Houseplant Formula as the main fertilizer for your hibiscus, you do not need to use extra magnesium. The HVH Houseplant Formula contains high doses of chelated magnesium in order to provide the extra nutrition that plants in less-than-optimal growing conditions need.