The Effects of Seaweed Fertilizer on the Growth of Plants

Growth

• Micronutrients found in seaweed fertilizer may improve plant growth and vigor, and prevent deficiencies in nutrients such as calcium or magnesium. Such deficiencies result in yellowed, or chlorotic, leaves. Growth hormones increase cell division, which influences plant growth and vigor.

Pest Control

• Seaweed fertilizer, combined with other ingredients, can control pests and diseases on roses and perhaps other plants, according to the University of Connecticut Soil Nutrient Analysis Laboratory. Mix 1 tablespoon. each liquid kelp fertilizer, insecticidal soap, horticultural oil, and bicarbonate-based fungicide with 1 gallon water. Spray roses and other ornamentals weekly with this solution to prevent aphids, black leaf spot, and powdery mildew.

Products

• Seaweed products are generally available in three forms -- extracts, cold-pressed, or enzymatically processed. Kelp meal is available in powdered form and is the most inexpensive of the three options. It has trace minerals but few growth hormones, and is often combined with fish emulsion for added nitrogen. It breaks down slowly when tilled into the soil. Kelp powder is similar to kelp meal but is water soluble for foliar applications, making the nutrients immediately available to plants. Liquid kelp is the most expensive option, but is either cold-pressed or enzymatically digested. Both formulas are rich in growth hormones and micronutrients, although enzymatically digested formulas are of slightly higher quality.

Considerations

• Seaweed fertilizers are relatively expensive and do not provide all the nutrients plants need. Use them infrequently to boost growth or improve foliage color, but do not forget to fertilize regularly with products containing nitrogen, phosphorus, and other major nutrients.