How to sow seeds

Sow thinly to reduce the risk of the seed being affected by a damping-off disease. This will also reduce the competition for light and so improve the quality of the germinated seedlings with less likelihood of them becoming straggly and stretched.

When sowing seeds, think of three plus 1 size categories; small, medium and large. The plus 1 category refers to seeds such as pumpkins, sweetcorn and courgettes which can be direct sown into a 9cm pot and therefore won’t require ‘pricking out’

Medium seed and this can include the seed of bedding plants such as ageratum or Agastache germinate best when covered with a thin layer of vermiculite. Use your presser board to provide a 2-5 mm gap for this seed size.

As a guide, expect to sow up to 50 tomato seeds in a 9cm pot, a smaller number for larger seeds.

Once you have finished sowing, using a presser board, gentle press the seed into the surface of the compost. This will help anchor the germinating seedlings when the radical (root) first emerges from the seed.

Now cover the seed with vermiculite by pouring over the top of the container out of a 9cm pot. Gently tap the surface of the vermiculite using the palm of your hand to level it off.  Make sure you don’t move any of the seeds underneath! The vermiculite will now be flush with the top of your container.

How should I water seeds and seedlings?

For best results water from below. Watering from above runs the risk of either disturbing the seed or the growing media or both. Stand the completed containers in a tray of tap water and allow the pot to draw up the water. Ensure that the complete soil profile becomes moist without getting waterlogged.

Getting watering right from the start means that it is unlikely that you will need to water again before most seeds germinate. Over-watering early on can lead to the spread of damping-off diseases and grey mould, both can cause seedlings to collapse and die.

To improve the health and vigour of your germinating seedlings consider the incorporation of Revive at the initial watering. Revive is a microbial treatment for compost and soil and contains a strain of Bacillus subtilis.

How do propagators help seeds to germinate?

Propagators work like a miniature greenhouse and create the optimum growing environment for seeds to germinate and grow, they provide essential heat and moisture-locking properties to ensure seeds get everything they need to get started. 

Writing in pencil add the name of the plant and the sowing date onto a plastic label. Insert a label into each pot. Place up to 10, 9cm pots into a small heated propagator ensuring that the clear plastic lid fits snugly over the top. If your heated propagator comes with a thermostat, for most seeds, set at 20°C.  Germination temperatures should be included on the seed packet. 

Moisture will quickly form on the lid of the container and perhaps every couple of days lift the lid and allow the water to run back down into the bottom of the propagator.

Germination times vary but within five days you will begin to see the seedling emerge through the vermiculite, it is at this stage that maximum light levels are required and you may now be able to remove the lid of the propagator all together or alternatively remove individual pots and place where they will receive maximum light levels. This will reduce seedling stretch and the risk of straggly seedlings.

Timing is critical and if it is too cold to place your recently germinated seedlings outdoors, in a cold frame or greenhouse then it was too early to start sowing seeds.

What is vermiculite and why is it important?

Vermiculite is a free-flowing, moisture-retentive and inert medium which when used as a covering for seeds, wraps the germinating seedlings in a warm, moist and humid ‘blanket’. This is ideal for germination. It also allows light to pass through it which for some seed species is important for germination.  Unlike if you cover with compost, vermiculite does not form a cap and the newly germinating seedlings will gentle ease their way through to the surface.