The vibrant flowering plants commonly referred to as indoor geraniums are actually members of the genus Pelargonium. These tender perennials, native to South Africa, have become a popular houseplant choice due to their striking, colorful blooms and often fragrant foliage. True geraniums belong to a different genus (Geranium) and are typically hardy, cool-weather plants. This article focuses on the specific care requirements for cultivating Pelargonium species indoors, ensuring they remain healthy and produce continuous flowers throughout the growing season.
Choosing Your Indoor Geranium and Potting Setup
Selecting the appropriate variety sets the stage for indoor success. Zonal geraniums (Pelargonium x hortorum) are a common choice for their upright habit and consistent flowering. Martha Washington varieties (Pelargonium x domesticum) are also popular, though they generally prefer cooler temperatures than Zonal types. Scented-leaf geraniums, prized for their rose, lemon, or mint aromas, are excellent indoor plants that offer fragrance when their foliage is brushed.
The container chosen must have excellent drainage holes, as these plants are highly susceptible to root rot in soggy conditions. Terracotta pots are a good option because their porous nature allows excess moisture to evaporate, promoting a healthier root environment. When potting, use a light, airy, and well-draining soil mix, such as a standard potting mix amended with perlite or coarse sand.
The ideal potting medium should not retain excessive water and may include components like peat moss or perlite to improve aeration. Geraniums prefer to be slightly pot-bound, so select a container that is only one size larger than the root ball when repotting. This preference for snug quarters helps regulate soil moisture and encourages the plant to focus energy on producing blooms rather than extensive root growth.
Mastering Light and Temperature Requirements
Providing sufficient light is essential for maintaining a flowering indoor geranium. These plants require a minimum of four to six hours of direct, unfiltered sunlight daily to support blooming. In the Northern Hemisphere, a south-facing window is generally the best placement, offering the most intense and prolonged light exposure throughout the day.
A west-facing window can also be suitable, delivering bright afternoon sun, but monitor for excessive heat buildup during summer. Insufficient light leads to etiolation, a condition where stems become weak and leggy as the plant stretches for energy. Poor light also directly reduces flower bud formation.
Geraniums thrive in a moderate temperature range, preferring daytime temperatures between 65°F and 75°F. They benefit from a slight cooling period at night, with ideal temperatures dropping to around 55°F to 60°F. This diurnal temperature fluctuation encourages better blooming. Avoid placing the plant near drafts or direct heat sources like vents, which can cause sudden temperature shifts and stress the foliage.
Watering and Nutrient Management
Proper watering involves allowing the soil to dry out partially between applications, as perpetually moist soil is the primary cause of root rot. A reliable way to assess moisture is the finger test: insert a finger a couple of inches deep into the soil, and only water if the soil feels dry at that depth. It is better to err on the side of underwatering, as geraniums tolerate temporary dryness well.
When watering, do so thoroughly until the water drains out of the container’s bottom holes, ensuring the entire root ball is saturated. Immediately empty any excess water that collects in the saucer to prevent the plant from sitting in stagnant moisture. During the winter months, when light levels are lower and growth slows, significantly reduce the frequency of watering to match the plant’s decreased metabolic rate.
Geraniums are heavy feeders during their active growing season from spring through fall, requiring consistent nutrient delivery to support continuous blooming. Apply a balanced, water-soluble fertilizer every two to four weeks, following the product’s dilution instructions to prevent chemical burn. A bloom-booster formulation high in phosphorus can also be used to encourage flower production. Halt all fertilization entirely during the winter dormancy period.
Pruning, Deadheading, and Pest Prevention
Deadheading, the removal of spent or fading flowers, conserves the plant’s energy and stimulates the formation of new buds. Snap the entire flower stalk off at the joint or node where it meets the main stem. This action prevents the plant from diverting energy into seed production, redirecting it toward vegetative growth and fresh blooms.
To maintain a dense, bushy appearance and prevent the stems from becoming sparse or “leggy,” practice light pruning by pinching back the growing tips. This encourages lateral branching, leading to a more compact plant structure. Remove any yellowing or dead leaves from the plant and the soil surface, as this decaying matter can harbor fungal diseases like Botrytis blight.
Indoor geraniums can attract common houseplant pests, including sap-sucking insects.
Common Pests
- Aphids
- Whiteflies, which often congregate on the undersides of leaves
- Spider mites, which create fine webbing
Regularly inspect the leaves, especially the undersides, for early signs of infestation. Treating with an insecticidal soap or horticultural oil, like neem oil, is an effective, low-toxicity method to control these pests.