Symptoms of Magnesium Deficiency in Pumpkin Leaves

Magnesium deficiencies can occur in sandy soils with low pH.

Pumpkins (Cucurbita spp.), which grow in U.S. Department of Agriculture hardiness zones 3 through 9, have become fall holiday icons and are thus late-season favorites for gardeners. Pumpkins vary greatly in size, ranging from 1 to 800 pounds, and can be uniformly round or long necked. Skins may be ribbed or smooth in colors from deep orange to white. Like any other Cucurbita, they suffer from deficiencies if soil conditions are not just right.

Seeing Spots

Symptoms of magnesium deficiency in cucurbits begin with interveinal chlorosis, or yellowing between the leaf veins on older leaves. The discoloration later turns up on newer leaves. The yellow spots eventually turn brown, die and fall off, creating a punch-hole appearance on the leaves. Symptoms can also include leaf curling and stunted growth. Magnesium deficiency occurs most often in sandy soils that have low cation exchange, a chemical process that substitutes one positively charged ion for another and makes magnesium deficiency more likely. Watch for signs of magnesium deficiency when the pumpkins are enlarging. Send soil samples to a soil analysis lab to confirm a deficiency in magnesium; most soil test kits sold at garden centers do not test for this nutrient.

Salty Treatment

To prevent magnesium deficiency, keep the pH of the soil at 6.5. Soil pH tests can be purchased at most gardening stores. Treatment can include water-soluble magnesium sulfate, commonly sold as Epsom salts, or magnesium oxide dispensed through drip irrigation. One tablespoon of Epsom salts per gallon of water may be sprayed on pumpkin leaves instead. Fertilizers containing potassium, calcium or ammonium should be used sparingly because these cations compete with magnesium in the soil.

Other Deficiencies and Toxicities

Pumpkin plants can develop other deficiencies. Manganese deficiency exhibits some of the same symptoms as magnesium deficiency: leaves turning yellow with veins remaining green. Adding manganese sulfate through foliar spraying can help to curb the deficiency. Use 1 tablespoon per gallon of water or as directed on the product label. Overliming is considered one of the primary causes of manganese deficiency. Manganese toxicity can also occur. It creates water-soaked areas on the underside of leaves and bronzed spots on the top and occurs when the pH falls low enough to allow more manganese to be available to the plant. Deficiencies and toxicities are best diagnosed through soil or pant tissue tests. Test your soil before treating to determine whether you have a magnesium or a manganese deficiency.

Basic Care for Pumpkin Plants

Pumpkins need a well-draining soil with a pH range of 5.5 to 6.8, with 6.5 being ideal. Before planting, till the soil 8 inches deep and spread 10 to 20 pounds of compost per 100 square feet. Plant when the soil temperature has reached 60 degrees Fahrenheit. Keep the soil evenly moist and avoid overhead watering. Spray plants with compost tea with 2 tablespoons of kelp meal per gallon of tea. Compost tea is made by placing compost in a burlap bag or old pillowcase and allowing it to steep in a bucket for three or more days. Both compost tea and kelp boost the plants' immunity by providing good bacteria that help the plant to better use nutrients such as magnesium.

About the Author

D. J. is the author of two children’s books. She has written articles on a number of topics including home improvement, pet care, health and physiology. Besides having studied journalism, she has degrees in business management and biology.