General gardening topics

How and when to grow lobelia from seed

Last updated on March 26th, 2021

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Lobelia seeds might look very small, and difficult to sow and handle but they are very easy to sow and very easy to germinate. The rewards you get from growing lobelia from seed are truly worth the effort. Trailing varieties of Lobelia such as Trailing Saphire or Trailing mixed can be grown in hanging baskets and containers to trail over the sides but bush varieties such as crystal palace, Cambridge blue and White lady are ideal for planting in beds and borders or just about anywhere else.

Lobelia growing in container in garden

What you need:

  • Your favourite varieties of Lobelia Seeds.
  • Seed tray, we recommend using seed trays with modules as this makes them easier to transplant.
  • Good quality seed compost

When you are growing plants from seeds you have a few options in terms of the tools you use. The containers can be purchased in the form of seed propagating trays and these are plastic trays that usually have a bottom section in which you placed the compost, and then a plastic lid that affixes to the bottom section with an adjustable knob at the top to control air circulation.

We recommend trays with individual models

Lobelia seedling growing in module seed tray

We recommend using trays that have individual models rather than once open trays as potting them up into pots later is much easier and disturbed the roots less.

Consider using a heated propagator

You could also use a heated propagator which will give a more consistent germination rate and they will also germinate more quickly than in a standard seed tray with no bottom heat. They are also fairly affordable too.

Making do with what you already have

Lobelia in clear cups

You can also recreate the same idea by planting in any container you have handy such as styrofoam cups or small plastic containers and plastic bags. When you put the plastic bag over the container you want to seal it to whatever the container is with a rubber band or something similar and prop up the plastic bag with something like sticks or pencils to keep the plastic from actually touching the plants as they are growing. 

Keep in a warm environment at a temperature of 15-20°C(60-68°F)

Having a place to put the tray or the containers is just as important as you need to maintain a constant temperature during the germination phase with access to a lot of indirect light such as a windowsill. Some people choose to use the growing lights to help this process or a heating mat underneath, and sometimes both.

Sowing Lobelia seeds

Lobelia in seed tray

When you get the seeds, you want to sprinkle them along the surface of a tray or containers. If you have a seed tray with individual modules, sprinkle some seeds into each modules.


Don’t cover them with anything because they require light to properly germinate. You can pat down the compost around them once you place the seeds on top.

Place the trays somewhere with regular temperatures between 15 degrees Celsius and 20 degrees Celsius. You can encourage germination by putting them in a heated propagator or onto a heated mat.

Water from the bottom if possible but placing the tray in a large tray of water so the compost can soak up water from below. Failing this we recommend watering with a spray bottle so that the tiny seeds are not washed around.

Germination should take between two and three weeks. You can sow the seeds from February onward but be advised that no matter when you start the process it will take about seven weeks before you can transplant outside but this should not be until the risk of frost has passed which is usually May.

Transplanting Lobelia seeds

Lobelia potted into pots and hanging basket

At that 7-week mark, when the seedlings are big enough to go into a larger container, it’s time to transplant. At this stage, you can choose to transplant them directly into the garden if the risk of frost has passed.

If you want to do this you can acclimatize the plants to the outdoor weather a few weeks beforehand but be careful not to introduce them to the outdoors until the risk of frost it’s over. Put them in a container or in the ground with rich, moist soil in a sunny position.

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