African Violets (Saintpaulia) are popular houseplants prized for their nearly continuous flowering under optimal conditions. Achieving consistent bloom requires a reliable supply of nutrients, making proper fertilization important. African Violets are considered heavy feeders but are exceptionally sensitive to the buildup of mineral salts, which can easily damage their delicate root systems. This sensitivity means the method and frequency of feeding are just as important as the product used, necessitating a precise and cautious approach.
The Optimal Fertilization Schedule
The question of how often to fertilize African Violets is answered by two primary schedules that focus on consistency. The most widely recommended approach is the “weakly, weekly” method, which involves applying a highly diluted fertilizer solution every time the plant is watered. This strategy provides a steady, low-dose supply of nutrients, mimicking continuous feeding and preventing periods of starvation.
The alternative schedule involves using a full-strength or half-strength solution less frequently, typically once every four to six weeks. This method is less common among experienced growers due to the risk of shocking the plant with a sudden high concentration of salts. The “weakly, weekly” method is safer and more effective for maintaining continuous growth and blooming because it avoids nutrient fluctuation. For this weekly regimen, the fertilizer is typically diluted to one-quarter or one-eighth of the strength recommended on the product label for monthly use.
Choosing the Right Fertilizer
The choice of fertilizer type is determined by its nutrient balance and the source of its nitrogen. African Violets thrive on a balanced diet of nitrogen (N), phosphorus (P), and potassium (K), represented by the NPK ratio on the label. A common general-purpose ratio like 20-20-20 or 14-12-14 is suitable for overall health, promoting both foliage and flower development.
For plants not blooming consistently, a formulation slightly higher in phosphorus, such as 12-36-14 or 10-30-20, encourages flower bud production. Select a water-soluble, quick-release liquid or powder fertilizer, as these are immediately available to the roots and allow for precise dilution. African Violets are sensitive to urea-based nitrogen, which can lead to root burn due to its acidic nature and high salt content. Therefore, the best products are those explicitly labeled as urea-free, using gentler sources like ammonium nitrate.
Application Techniques to Prevent Damage
Applying fertilizer safely requires careful attention to dilution and watering method to prevent root damage from salt buildup. When using the “weakly, weekly” schedule, the fertilizer must be diluted significantly, often to a quarter or less of the manufacturer’s suggested dose. Use room-temperature water for mixing and application, as cold water can cause unsightly spotting on the leaves.
The most effective way to deliver the nutrient solution is through bottom-watering, where the pot is placed in a saucer of the diluted fertilizer until the soil surface becomes moist. This technique prevents water from touching the plant’s sensitive crown and leaves, which can lead to rot or spotting. Because bottom-watering can contribute to the accumulation of fertilizer salts at the top of the soil, the soil must be “flushed” periodically. This involves pouring a large volume of plain, room-temperature water through the soil until it drains freely from the bottom, washing away excess mineral deposits. This process should be performed every few months.
Seasonal and Growth Cycle Adjustments
Fertilization schedules should be adjusted to align with the plant’s metabolic rate, which is influenced by light and temperature. African Violets are typically fertilized year-round because they can bloom continuously under consistent indoor lighting. During periods of naturally low light, such as winter, or when temperatures are cooler, the plant’s growth slows down.
When the plant is not actively growing or flowering, the fertilizer concentration should be reduced by half, or the frequency extended to every six to eight weeks to prevent nutrient overload. When a plant is sustaining a heavy bloom cycle, maintaining the regular “weakly, weekly” schedule provides the necessary phosphorus and other nutrients utilized during flower production. Newly repotted African Violets should be given a break from fertilization for three to four weeks to allow the root system to recover and settle into the fresh soil mix.