Geraniums, scientifically known as Pelargoniums, are flowering plants known for their vibrant colors and long blooming season. To achieve a prolific display of flowers, they require proper nutritional support. Timely and appropriate fertilization significantly influences their overall health, foliage quality, and continuous flower production throughout the growing season.
Seasonal Fertilization Timing
The feeding schedule for geraniums aligns with their active growth cycle, starting in the spring after the danger of frost has passed. Fertilization should begin once the plant is established and shows signs of new growth, signaling its transition out of dormancy. An initial application of a slow-release granular fertilizer at the start of the season can provide a foundational, steady supply of nutrients for several months.
Supplementing this with a water-soluble or liquid feed during the peak summer months encourages continuous blooming. During maximum growth and flower development, a regular regimen of feeding every two to four weeks is recommended. This frequent, diluted application ensures the plant has a steady stream of the necessary elements to sustain its high energy output.
As autumn approaches, reduce fertilization frequency to once a month, then cease entirely in late fall or early winter. Stopping fertilization is important because the plant naturally slows its growth and enters a period of rest. Applying fertilizer when the plant is dormant can lead to a harmful build-up of salts in the soil, damaging the roots.
Selecting the Appropriate Fertilizer Type
Geraniums require a specific balance of Nitrogen (N), Phosphorus (P), and Potassium (K), represented by the N-P-K ratio. This ratio is adjusted to prioritize flowering over excessive vegetative growth. A balanced fertilizer, such as 10-10-10 or 20-20-20, can be used for general health and foliage development.
For maximum flower production, the geranium benefits from a fertilizer with a higher middle number (Phosphorus). Phosphorus (P) is directly involved in root development and the initiation of flower buds. Ratios like 15-30-15, which emphasize phosphorus, are recommended once the plant begins to set buds.
Excessive Nitrogen (N) promotes lush, green foliage at the expense of blooms, potentially leading to leggy plants. Potassium (K) assists with cellular function and improves the plant’s resilience to disease and environmental stress. Fertilizers come as water-soluble liquids for quick uptake or granular slow-release options for continuous feeding.
Adjusting Feeding Based on Growing Environment
The geranium’s physical location significantly impacts its nutritional needs and required fertilization schedule. Geraniums grown in containers require more frequent feeding than those planted directly in the ground due to the limited volume and nutrient leaching.
When container plants are watered thoroughly, essential nutrients are washed out of the potting medium with the excess water. This process, known as leaching, depletes the available mineral salts more rapidly than in garden soil, which has a larger reservoir. Container-grown plants thus benefit from consistent feeding, often every two to four weeks, to replace lost nutrients.
In-ground geraniums have access to a larger soil volume, retaining nutrients more efficiently. These plants require less frequent feeding, often every four to six weeks, especially if the soil is amended. When overwintering geraniums indoors or allowing them to go dormant, suspend all fertilization until new growth resumes in the spring.
Identifying Signs of Nutrient Imbalance
Observing the plant’s foliage and growth habit provides visual cues that the fertilization routine needs adjustment. A common sign of under-fertilization or deficiency is chlorosis, the yellowing of leaf tissue. Nitrogen or magnesium deficiencies often appear first on older, lower leaves as the plant mobilizes these mobile nutrients for new growth.
Conversely, over-fertilization results in a high concentration of soluble salts in the soil, damaging the plant. Symptoms include the browning or “burning” of leaf margins and tips, as high salt concentration draws moisture out of the roots. In severe cases, over-fertilization can lead to blackened, rotting roots and a sudden decline in plant health.
An imbalanced feed is indicated by the plant’s growth structure. Excess nitrogen causes the plant to become “leggy,” producing abundant leaves but few flowers. Stunted growth and poor flower production, despite adequate water and sun, suggest a general lack of available nutrients, particularly phosphorus. Timely diagnosis allows a gardener to adjust the fertilizer type or application rate before permanent damage occurs.