Irises, cherished for their vibrant blooms, are a popular addition to many gardens. Providing them with proper nutrition is important for their health and abundant flowering. Homemade fertilizers offer a natural, cost-effective, and environmentally conscious way to support iris growth, leveraging readily available materials to enhance soil fertility.
Understanding Iris Nutritional Needs
Irises require a balanced supply of essential nutrients for optimal development. Phosphorus is important for strong root development and prolific bloom production. Potassium supports overall plant health, contributing to sturdy stems, vibrant flower color, and enhanced disease resistance. Nitrogen, while necessary for healthy foliage growth, should be applied sparingly, especially for rhizomatous iris varieties. Too much nitrogen can lead to excessive leafy growth at the expense of flowers and can increase susceptibility to rot diseases.
Common Homemade Fertilizer Options for Irises
Various household and garden materials can be repurposed into effective homemade fertilizers for irises, each offering a unique nutrient profile.
Compost
Compost provides a wide array of nutrients and improves soil structure and drainage. Spread a 1-2 inch layer of finished compost around the base of iris plants, ensuring it does not directly cover the rhizomes. Compost tea offers a liquid alternative, delivering soluble nutrients directly to the root zone. To make compost tea, submerge mature compost in water for several hours or overnight, then strain and use the liquid to water your irises.
Bone Meal and Eggshells
Bone meal is a source of phosphorus and calcium, crucial for strong root systems and abundant blooms. Incorporate approximately 1 tablespoon per rhizome into the soil around irises, ensuring it is mixed in, not resting directly on the rhizome. Eggshells also contribute calcium, important for cell wall development. Rinse, dry, and crush eggshells into a fine powder before incorporating them into the soil.
Coffee Grounds
Coffee grounds supply nitrogen and micronutrients, and can slightly acidify the soil. Used coffee grounds are closer to neutral pH after brewing. Apply sparingly by mixing them into the topsoil around plants to avoid compaction and potential issues from caffeine residues.
Wood Ash
Wood ash contains potassium and calcium, and can raise soil pH. Use cautiously and only after a soil test confirms a need to increase pH. Incorporate a small amount into the soil.
Epsom Salts
Epsom salts provide magnesium and sulfur, important for chlorophyll production and overall plant vigor. Irises generally do not require large amounts of these minerals, so use Epsom salts only if a magnesium deficiency is suspected, indicated by yellowing leaves between the veins. A light application, such as 1 tablespoon per gallon of water, can be used as a targeted liquid feed.
Applying Homemade Fertilizers Effectively
Proper application of homemade fertilizers ensures irises receive the most benefit without adverse effects. Irises generally benefit from being fertilized twice a year. The first application should occur in early spring as new growth emerges, about a month before the blooming season. A second feeding is beneficial about a month after flowering, which helps the plant store nutrients for the following year’s blooms.
Homemade fertilizers can be applied through various methods. Top-dressing involves spreading solid materials like compost or bone meal on the soil surface around the plant. Side-dressing places the fertilizer in a ring around the plant, away from the rhizome. Liquid feeds, such as compost tea, are watered directly into the soil.
Moderation is key when fertilizing irises to avoid over-fertilization. While specific dosages depend on the chosen material, apply lightly and evenly. Always water the plants thoroughly after applying any granular or solid fertilizer to help nutrients penetrate the soil and become available to the roots.
Important Considerations and Precautions
When using homemade fertilizers, understanding certain factors can prevent potential issues and promote healthy iris growth. Soil pH is an important consideration for irises, as most bearded irises prefer a slightly acidic to neutral pH, ideally around 6.5 to 6.8. Some homemade options, like wood ash, are alkaline and can significantly increase soil pH, while others, like coffee grounds, have a minor and short-lived effect on acidity. Conducting a soil test before applying amendments helps determine current nutrient levels and pH, guiding appropriate choices.
Over-fertilization can harm irises, leading to signs such as burnt leaf tips or reduced blooming. Irises, particularly bearded varieties, are sensitive to high nitrogen levels. Excess nitrogen promotes lush, leafy growth at the expense of flowers and can increase the risk of soft rot, a common disease in irises. Therefore, choosing low-nitrogen options or using high-nitrogen materials very sparingly is important.
Iris rhizomes, the fleshy underground stems, should not be buried too deeply when planting or when applying fertilizer. For many iris types, the top of the rhizome should be at or just barely below the soil surface, as burying them deeply can lead to rot. When applying granular fertilizers, spread them around the rhizomes and gently work them into the soil, ensuring they do not rest directly on the rhizome.