The easiest and most common way to start geraniums from seed is indoors using peat pellets in seed starting trays. You can buy them already populated, or reuse trays you already have, just buying the peat pellets to refill the trays. Sowing in seed starting trays has multiple advantages:
- The seeds/seedlings can be watered from the bottom, making damping off less likely.
- You won’t have to thin a bunch of geraniums; just plant a couple per cell and choose the strongest for transplant, plucking the weakling out.
- The temperature can be controlled more easily, either with a heat mat or by consistent light/heat from a heat lamp. (The seeds don’t need light to germinate, but the seedlings will need plenty.)
- The moisture level can be more easily maintained and monitored.
- Seed starting trays are more attractive and use space more economically than wax paper cups, egg cartons or re-purposed yogurt containers. And they are reusable, nesting neatly when not in use.
- Peat pellets, as opposed to other planting mediums, will not contain the fungus that causes damping off. (If you are using containers that have been used for other plants, be sure they are clean and have drainage holes to prevent damping off. After washing in soapy water, mix one part chlorine bleach to nine parts water to disinfect them. This is especially necessary if repurposing the small pots you get in the garden section or from the nursery.) If your seedlings have been infected, the stems will thin at the soil line and the plants will just break off; not a pretty sight and disappointing, to say the least.
- The peat pots can be transplanted whole, which means less chance for breaking the delicate stems. We recommend holding the seedlings gently by the leaves if you have to handle them at all.
Sow the seeds about 1/8 inch deep, putting two or three seeds per cell or pot, discarding the weakest after the first true leaves appear, thinning to 1 plant per pot. (The first leaves are called seed-leaves or cotyledons and will eventually wither or fall off; wait until the second set of leaves is growing well before thinning.)
Geranium seeds germinate best at consistent soil temperatures of 72°F. If not watering from the bottom, keep the soil moist by misting so as not to dislodge the seeds; use room-temperature water to maintain soil temperature. Germination can take from 5 days to 4 weeks, so be patient.
If growing under a dome, cant the dome slightly once the seeds start sprouting to provide air circulation while still maintaining moisture levels. Once your geranium seedlings are growing strongly, or touching the dome, remove it completely.
Fluorescent lights, grow-lights or adequate natural light must be utilized once the seedlings are growing well and are at least one week old. If you have insufficient light, they will become spindly and frail as they stretch to find the sun, though exposing them to strong sun too soon may result in their demise. We recommend 12 to 14 hours of light a day, ensuring the planting medium stays consistently moist, but not wet.
To promote fuller, more compact and well-branched plants, nip the new growth once or twice after the seedlings are growing strongly (usually with 4-6 true leaves).
You can also transplant at this time, either into your decorative containers, or into the garden after hardening off. Handle the seedlings very carefully, avoid disturbing the roots, and use as much of the soil they’ve been growing in around the roots as possible. (This is where those peat pellets really come in handy; the whole thing can be transplanted.)
When moving your geranium seedlings outdoors, you need to harden them off first, which simply means exposing them gradually to outdoor conditions. The daytime temperatures should be at least 70°F with nighttime temperatures not dropping below 55°F before you even think about moving them out. Set the pots or seedling trays in a shady, sheltered spot to begin with, leaving them out for half days at first, gradually increasing the time and slowly moving them into sunnier and less sheltered spots over a period of about two weeks. If they’ve been out overnight for two or three nights and they still look strong and healthy, they’re ready for the garden or permanent outdoor placement. If nighttime temperatures happen to drop unexpectedly, simply cover them with a plant cover or sheet or move your potted plants into a greenhouse or cold-frame.
So now you know just about everything you could possibly want to know about starting geraniums from seed. We’d love to have you share your successes with us. Send pics!
As always, we wish you happy gardening, and in this instance, lots of gorgeous geraniums!