Cheerful geraniums (Pelargonium x hortorum), hardy in U.S. Department of Agriculture plant hardiness zones 10 and 11, are grown outdoors year-round within their hardiness zone. Outside that range, they frequently spend the growing season outside and overwinter indoors. To keep geraniums healthy and blooming regularly, the plants must be watered when dry and fed with either commercial or homemade plant foods. Epsom salts and bone meal work in different ways to help fulfill the plants' needs.
1. Geranium Requirements
Geraniums grow best in soil with soil pH that ranges from slightly acidic to somewhat alkaline, with pH levels of 6.0 through 8.0. Adding Epsom salts, or magnesium sulfate, to soil or potting mix around geraniums will not change the soil pH level. Adding bone meal will make soil more alkaline. If you are in doubt about the pH level of the soil in the garden or in containers, invest in a soil test kit, available from nurseries and garden centers. Do not add bone meal if the soil is already at pH level of 8.0.
2. Epsom Salts and Bone Meal Benefits
Adding Epsom salts to either garden or potted plants adds magnesium to the soil, correcting deficiencies, if they exist. Epsom salts may also help promote bushy growth and increase flower production. Care should be taken not to overuse Epsom salts, as salt build-up may lead to leaf damage. Bone meal is made from animal bones and acts slowly in the soil. It contains 12 to 20 percent phosphorus, which may stimulate root and flower growth. All-purpose plant foods also contain phosphorus, in percentages defined by the middle number of the three numbers on package labels, for example, 12-4-8.
3. Epsom Salts and Bone Meal Application
Combining Epsom salts and bone meal in a single recipe is less useful than applying them separately, because the two substances act differently. Fast acting Epsom salts are water-soluble. Use 1 tablespoon Epsom salts per gallon of water and spray on foliage every two weeks. Alternately, water with the same solution every two weeks as part of a regular watering schedule. Slow-acting commercial bone meal is not water-soluble. Ideally, it should be mixed with soil at planting time at a concentration of one part bone meal per 20 parts soil or 1 tablespoon per gallon of soil.
4. Nutrient Considerations
Using Epsom salts and bone meal will increase the health of geraniums by supplying only two nutrients, magnesium and phosphorus. This may be useful if the geraniums are suffering deficiencies of those nutrients. Otherwise, a balanced commercial plant food, such as12-4-8, may be a better choice for more balanced nutrient delivery. The plants also need well-drained soil and at least six hours of direct sunshine per day. Water only when the surface of the potting medium feels dry to the touch. Good air circulation around the plants is an important means of discouraging fungal diseases.
- MIssissippi State University Extension Service: Soil pH and Fertilizers
- Fine Gardening: The Pros and Cons of Bone Meal
- Alberta Agriculture and Rural Development: Houseplants: Fertilizer
- Tagawa Gardens: Basic Houseplant Care
- Missouri Botanical Garden: Plant Finder -- Geranium x Hortorum
- Clemson Cooperative Extension: Growing Geraniums Indoors
- Hewitt's: Bone Meal
- Washington State University Extension: The Myth of Beneficial Bone Meal
- Washington State University Extension: Myths: Adding Epsom Salts to Gardens is a Safe, Natural Way to Increase Plant Growth
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