Geraniums have been a popular bedding plant for over a century now, and why not? They are tough, tolerant of drought and relatively disease and pest resistant.
While geraniums have been traditionally grown from cuttings, new seed-grown hybrids have been becoming increasingly popular. Why? Because they will often out perform the older geranium varieties. This is Because many of these new seed-grown hybrid geraniums possess excellent vigour and heat tolerance, superior disease resistance, and will flower their hearts out until the first frost of winter.
Luckily, geraniums are easy to grow from seed although they are rather slow to get going. To get the most out of growing geraniums from seed you will need to sow their seed from mid - to late January. This gives you the best chance of to produce flowering plants ready for the spring. Typically, your geranium seedlings will be in flower approximately 12 to 16 weeks after sowing.
When choosing your compost, keep in mind that good drainage is a priority. Choose a good quality soil based medium such as John Innes 'Seed and Cutting' but add either horticultural grit or perlite at a 3:1 ratio in order to improve drainage.
During germination, the biggest killer of geranium seedlings are fungal diseases - notably 'damping-off'! To discourage damping-off, containers used for starting seed should be clean and have excellent drainage. If you are re-using old containers then they should be washed in soapy water, then disinfected by dipping in a solution containing one part chlorine bleach and nine parts water. make sure you thoroughly rinse them off with clean water afterwards though.
Using either, pots, seeds trays or preferably modular trays,fill with your compost to within 1/2 to 1 inch of the top. Firm the medium lightly, water, then allow any excess water to drain away. geranium seeds can be sown 2 to 3 inches apart and cover with about 1/8 inch of compost. After sowing, thoroughly water the compost by partially submersing the pot or tray in water. When the surface becomes wet, remove the container from the water and allow it to drain thoroughly. To insure a uniform moisture level during the germination period, cover the container with a sheet of glass or clear plastic. Failing that you can try cling film, but don't let it sag in the middle.
Move your pot or tray in to a warm position where it will receive plenty of bright light, but out of direct sunlight. This is because direct sunlight can cause high temperatures which may adversely affect seed germination. The ambient temperature will need to be about 75 degrees Fahrenheit. Your geranium seeds should germinate in five to seven days. Remove the plastic/glass covering as soon as germination occurs.
Transplant seedlings into individual containers when the first true set of leaves appears. Again, consider using a good quality soil based compost such as John Innes 'No 1', but mix in additional horticultural grit or pelite for improved drainage. Just remember to handle the small seedlings by their leaves since the small, thin stems can break easily. Insert seedlings to the base of the seed leaves, called cotyledons, when transplanting.
Growing tips for geraniums from seed
For best results, grow seedlings under fluorescent lights. The lights should be no more than 4 to 6 inches above the growing plants. Leave the lights on 12 to 16 hours per day. If supplemental lighting is unavailable, place the plants in a sunny south window. Geraniums become tall and spindly when grown without sufficient light. Pinch out the shoot tips of spindly plants to encourage branching.
Ideal growing temperatures for geraniums are 70 to 75 degrees Fahrenheit during the day and 60 to 65 degrees at night. Thoroughly water geraniums when the soil surface is dry to the touch. Fertilise weekly with a one-quarter strength house-plant fertiliser. Harden off the plants outdoors for seven to ten days before planting into the garden. Plant geraniums outdoors when the danger of frost has passed.