Citronella refers to two distinct plants: the true citronella grass (Cymbopogon nardus or C. winterianus) and the scented geranium often sold as a “mosquito plant” (Pelargonium citrosum). Although the grass is the source of commercial citronella oil, the scented geranium is the variety most frequently grown by home gardeners. Growing either plant from seed is possible, but it is often more challenging and time-consuming than purchasing established nursery starts. Due to the delicate nature of the seeds and specific warmth requirements, starting indoors is necessary for success.
Essential Pre-Planting Conditions
Successful germination requires preparing the right indoor environment well before the last spring frost. Start seeds approximately 8 to 10 weeks before the final frost date to ensure seedlings are robust enough for outdoor planting. This early start compensates for the plants’ slow initial growth and their strict requirement for warm soil and air temperatures.
Use a sterile, fine-textured seed-starting mix instead of standard potting soil, as it provides optimal drainage and prevents “damping off.” Shallow trays or small containers with adequate drainage holes are best for sowing the tiny seeds. A location receiving full sun or, more reliably, artificial grow lights for 14 to 16 hours daily is necessary to mimic the plant’s tropical origins.
The ambient temperature must be consistently warm, ideally between 70°F and 75°F, to encourage sprouting. Placing the seed trays on a specialized heat mat can maintain this temperature range, which is often difficult to achieve with ambient room air alone.
Step-by-Step Sowing for Germination
Before sowing, saturate the seed-starting mix until it is uniformly moist but not soggy, allowing excess water to drain completely. This pre-moistening prevents the tiny seeds from being washed away during later watering. Since citronella seeds require light to germinate, surface sowing is the most successful technique.
Gently sprinkle the seeds across the surface of the soil mix, aiming for sparse distribution to minimize thinning later. Do not cover the seeds with soil. Instead, use a flat object to gently press the seeds onto the surface, ensuring firm contact with the moist medium for water absorption.
To maintain the required high humidity and warmth, cover the seed tray with a clear plastic dome or plastic wrap. Place the covered tray on the heat mat under the grow lights, checking the soil daily to ensure it remains consistently damp. Germination is erratic, typically occurring within 7 to 21 days, though some seeds may take up to six weeks to emerge.
Transitioning Seedlings to the Garden
Once seedlings develop their second set of leaves, they are ready for the next phase of growth. Thin the seedlings by snipping the weaker plants at the soil line, leaving only the strongest one or two per cell or pot. This ensures the remaining plants have sufficient space and resources to develop robust root systems.
“Hardening off” prepares the indoor-grown plants for the outdoor environment. Begin by exposing the seedlings to the outdoors for only one or two hours daily in a sheltered, shady spot protected from direct sun and wind. Over 7 to 14 days, gradually increase their outdoor exposure and introduce them to filtered sunlight and gentle breezes.
Transplanting can occur after all danger of frost has passed and nighttime temperatures consistently remain above 50°F. Handle seedlings carefully by their leaves or root ball, avoiding the stem. Dig a planting hole slightly wider than the root ball, gently ease the plant from its container, and loosen any matted roots before settling it into the garden bed or a larger container.
Long-Term Care and Harvesting
Once established, citronella requires consistent moisture, especially during intense summer heat. Water deeply whenever the top inch of soil feels dry, ensuring the soil drains well to prevent waterlogging and root rot. Excessive fertilization is unnecessary and can lead to weak, leggy growth.
If growing in containers or nutrient-poor soil, apply a balanced, water-soluble fertilizer diluted to half-strength every two to three weeks. Regular pruning is beneficial for shaping the plant and encouraging a dense, bushy growth habit. Pinching off the tips promotes lateral branching and results in a fuller plant.
In most temperate zones, citronella is cultivated as an annual since it is sensitive to cold. Before the first expected frost (when night temperatures dip below 45°F), plants can be potted and moved indoors to a sunny window to overwinter. Snip the foliage as needed throughout the growing season for harvesting; this encourages new growth.