I’ve been asked a lot about my approach to sowing seeds and it seems an opportune time to write about that. Though some seeds are best started off in pots (tomatoes, aubergines, celery), the majority of my seed sowing is done in module trays. A module tray is a tray with individual compartments or modules in it. A decent sized tray will measure 335 x 515mm and have between 80 and 150 modules in them. They are made from tough plastic so they can be used again and again. The beauty of a module tray is that the roots of seedlings are kept apart which means you don’t upset them when you are transplanting them.
Before you fill the tray with compost, it’s important to work with the compost a little first. Break up any larger clumps – this is important because smaller seeds might fall down through the cracks and fail to germinate because they’re too deep in the compost. I start by completely overfilling the tray with compost and working it in to the modules with my hands. Banging the tray against the bench a few times will help the compost to settle down in to the container. Overfill it again. Then, I use a flat stick or piece of timber to ‘slice’ the excess compost off the top of the tray, leaving a flat, clean surface on the module tray.
Before sowing the seeds I make a ‘divot’ in each module with my fingers. This is the little recess in the compost in to which you will drop the seed. I usually use two fingers from each hand to do four modules at a time to speed things up! How deep you make the divot depends on how deep the seeds need to be. A good rule of thumb is that you sow the seed roughly twice as deep as the seed’s size. So, a tiny lettuce seed is almost on top of the surface, while a larger seed like a squash or pumpkin would be much deeper.
Depending on the size of the seed, you can either pick one up and drop it in to the divot; or use a plant label to move it off the palm of your hand and let it fall in to the divot. With most vegetables, you will be sowing one seed per module but with others (e.g. oriental greens) you might be sowing 3-4 seeds per module. It’s really important to label the tray. I use white plastic labels and a pencil so they can be washed off and reused. I always write the name of the veg, the variety and the date it was sown on the label, so for e.g. “Beetroot, Detroit Globe, 17/04/17”). That way if germination is slow you can check how long it was since it was sown.
To cover the seeds, I then overfill the tray with compost again and slice the excess off with my trusty stick to leave a flat surface again. I then bring the trays outside and water them on the ground outside the potting shed. I use a fine mist setting on the hose, but a fine rose on a watering can is just as good. Check out the videos in the Get Growing section of giy.ie to see the seed sowing in action.
The Basics – Top Tips for Seed Sowing
If you are still not having success with your seed sowing, keep an eye out for the following:
Planting Depth – you could have sowed your seeds too deep or too shallow. Check the seed packet and try again.
Old seed – seeds that are past their “sow before’ date will often struggle to germinate. It’s a good idea to discard old seed or at least do a germination test before sowing big quantities. Make sure you are buying good quality seed.
Temperature and Water – different vegetables have different requirements in terms of their preferred temperature and the amount of water they get.
Mould – a formation of mould on the surface of the soil is often a problem when the temperature is cold and the trays have been overwatered. Poor ventilation can compound the problem. Placing a fan in the area will keep air circulating.