Seed Sowing Indoors

Now is the time to think about sowing seeds. Whether you want to grow some bedding plants, a few perennials for the border or some vegetables, now is the time to make a start.

But before you do, it is important to get to grips with the basics to make sure you are successful. Seeds are good value but they are not ‘cheap’ so it is vital that they get the best start. This guide is for is sowing seeds in warmth, in the greenhouse or on the windowsill.

We will deal with seeds you can sow direct where they are to grow in coming weeks.

Seeds vary in their needs but most of those you are likely to grow all need similar conditions.

What you need

Seed trays – for seed sowing you do not need deep containers. Small seed trays or ‘cell trays’ are best. These must be new or clean. If you use dirty pots or trays, they will be infected with disease (or have slugs on them) and that results in failure.

Compost – the compost must be fresh and free from disease. Buy a new bag and do not use ‘leftover’ compost from last year. Seeds do not need high nutrient levels to germinate so do not use ‘mature plant’ composts.

Vermiculite – this expanded rock (along with perlite) is added to compost to ‘aerate’ the compost, improving drainage. Add between 10% and 20% by volume to the compost, especially for ‘delicate’ seedlings. You do not need to add it if sowing large seeds like courgettes or beans but it is also useful to cover small seeds – it allows light to reach the seeds, which is often beneficial, and keeps humidity around the seeds as they grow.

Water – always use tap water when sowing. Water from a water butt can be contaminated with fungi and bacteria

Sieve – a sieve is useful to prepare a fine surface for sowing. But you can often use a flower pot – put some compost in the pot and shake over the sowing area. Or you could use an old colander.

Propagator – seeds need warmth to germinate. A temperature of about 20c (from 15-25) is ideal to germinate most seeds. Any lower and seeds may just rot in the cold, wet compost. Any higher and seedlings may become ‘stretched’ and difficult to handle. You can buy an electric ‘heated’ propagator and those with a thermostat are best to avoid excessively high temperatures on a sunny day. But you can cover the seed pots or trays with a clear plastic cover of any kind. In the greenhouse you can simply cover with a sheet of plastic or fleece – to retain some heat and moisture. You will need to remove and shake the plastic covering every day to remove excess moisture. Propagator lids will have ‘vents’ so you can gradually acclimatise seedlings to outside conditions. Never let plastic sheets lay on the actual seedlings or they will be prone to rotting.

Watering

It is often suggested that you water your seeds or seedlings with a ‘mister’. This is usually a bad idea because keeping the seedlings constantly moist will lead to ‘damping off’. Damping off is a fungal disease that ‘creeps’ through the compost and will kill the seedlings at soil level, causing them to ‘topple over’. It can kill all your seedlings in a few days. Regular misting will make matters worse. It is best to water the trays before sowing. You may then not need to water again for at least a week and usually not until the seedlings appear – then water by placing the seed trays in a tray of water so you water them from below and do not get the seedlings wet.

Growing-on

As soon as the seedlings appear they will need to be transplanted into pots or cell trays to grow on. They will then need good light and some warmth to grow. If you are sowing on a windowsill you need to prepare yourself for this – one pot of seeds may become a hundred pots of plants! They cannot be placed outside until mid-April and not planted till Mid-May. If you sow too early you will struggle to keep your seedlings healthy and ‘sturdy’.

Seed packets will give a range of sowing times but late sowings always catch up (within reason) and are best if you are sowing on the windowsill. If you have a greenhouse, where light levels are higher, you can sow a bit earlier. Even with a greenhouse I do not sow till early- to mid- March.

It is also important to ‘harden off’ seedlings before you plant them. It is important that your seedlings are acclimatised to outside conditions before planting them out, especially if they have been grown in the home. Without wind and direct sunlight they will be ‘soft’ and will scorch when suddenly planted outside. So move them outside on cloudy, mild days in late April and bring them back in on cold nights.

Summary

  • Fill your trays. Fluff up the compost, mixing in some perlite if you like. Fill the trays loosely and tap them to settle the compost. NEVER press it down.
  • Water the trays before you sow. You can put them into a tray of water to soak them if you have time. Let them drain for an hour if possible. Always use clean tap water.
  • Sow the seeds thinly. This will make them easier to transplant later and will make damping off less likely.
  • Cover with sieved compost or a thin layer of perlite or vermiculite. You do not need to water again so you will not be washing tiny seeds into the compost.