Seed sowing and germination tips

Man putting seed in plant cell tray
Start your seeds off in a plant cell tray
Image: Garden Grow Plug and Seed Growing Tray from Van Meuwen

Sowing seeds is a cheap and easy way to grow plants, flowers, fruit and veg. And it’s incredibly satisfying when you see the process through from start to finish. Here are our top tips for successfully germinating seeds and caring for young seedlings. 

Browse our full collection of vegetable seeds and view our excellent range of flower seeds for inspiration.

Seed germination tips

Double heavy-duty green cloche
A heavy-duty cloche helps warm up the soil before sowing
Image: Garden Gear Apex Cloche from Van Meuwen (©Thompson & Morgan)

Provided you meet their basic needs, most seeds are fairly easy to germinate. Along with good quality compost, they need the correct levels of light, water, heat and air. Remember that not all seed failure is your fault. Here’s how to get the best germination rates.

Get the temperature right

Seed packs often show a recommended temperature for germination, and it’s important that your seeds are not too hot or too cold.

If you’re starting your seeds off indoors, most require a temperature of 13C – 21C. This can be achieved by growing them on a sunny windowsill or a heated propagator. As soon as the seedlings emerge, remember to move the trays to a cooler spot so the young leaves won’t scorch.

If you’re direct sowing your seeds outdoors, check the seed packet to see which months are recommended. This is only a guide, as different parts of the country have very different temperatures. In colder parts of the UK, you might like to warm the soil up for a few weeks by covering it with cardboard, black plastic or cloches. Avoid sowing seeds when the ground is cold and waterlogged, as they are likely to rot.

Get the moisture level right

Make sure your seeds have just the right amount of moisture in order to germinate.

If you’re starting seeds indoors, prepare the compost by watering it and letting it drain before you sow. If the surface starts to dry out, stand the seed tray in water until the surface becomes moist again, then let it drain.

If you’re direct sowing outdoors, prepare the soil in advance to give your seeds the best chance. Add plenty of organic matter and homemade compost to your beds, containers and window boxes to help the soil retain moisture while also draining well.

Get the planting depth right

Check the sowing depth recommendations on the seed packet before sowing. No instructions? Seed size is a good indicator of how deep to sow.

  • Very small seeds need just a light covering of sieved compost or vermiculite
  • Larger seeds need to be sown several centimetres under the surface
  • As a rule, most seeds should be planted at a depth of 3 or 4 times their own width

Protect your seeds from pests

Deter pests such as mice and birds from eating your seeds by covering your sowings with netting, cloches or chicken wire. It’s important to check netting frequently, as it can trap birds or other wildlife.

Look out for specialist instructions

Some seeds need special treatment before you can sow them. If the packet says that chilling, chipping or soaking is needed, don’t skip this essential step.

Check the use-by date

Your seed pack should show a ‘sow by’ date. If this date has passed, some of your seed may still germinate but at a much lower success rate. We recommend buying new seed each year, especially for crops like parsnips that rarely succeed from old seeds.

Top tips for successful seedling care

Spraying seedlings in individual pots on windowsill
Once your seedlings have developed their ‘true’ leaves, move them into their own pots
Image: Shutterstock

Seedlings should be pricked out and potted on into individual pots once they’re large enough to handle. If left in the seed tray, they’ll quickly run out of the space, light and nutrients that they need, and start to look sickly. Here’s our best advice to help you care for your young seedlings.

Carefully prick seedlings out at the right time

Is your seedling ready to pot on? If the first set of true leaves has formed (not the cotyledons) it’s a good indication that the plant is almost ready to be transplanted out of its seed tray. Gently lift your seedlings out of the seed tray with a dibber and check the roots – if the roots are very tiny, leave the plant to grow on for a few days. It’s important that seedlings have sufficient root growth to cope with the transplanting process. Here’s how to handle delicate seedlings:

  • Always lift your seedlings gently, using a dibber to lift the roots from within the soil
  • Use the first leaves that formed (cotyledons) as handles if you need to touch the plant
  • Never handle a seedling by its roots or stem, as these are too delicate.

Take care not to leave it too late. If you delay pricking out your seedlings they will start competing for space, light and nutrients. Fast-growing plants quickly become sickly and growth will be delayed – even after potting on your plants may never recover and reach their full potential.

Make sure your seedlings have enough light

If your seedlings aren’t receiving enough light, they’ll strain to reach it. If the room is warm, you can end up with rapid growth but tall and leggy plants that flop over easily and don’t support their own weight. Always grow your seedlings on a bright windowsill but out of strong sunlight, which can scorch the young leaves.

Look out for fungal diseases like damping off

Damping off is a common reason that seedlings die or rot away at the base. It’s caused by fungal diseases that occur in wet soil, so you can reduce the risk by using brand new compost, disinfecting your pots and seed trays, and letting the compost dry out slightly between waterings. Always make sure your plants are well ventilated with good air flow around them, and use clean tap for watering while they’re still small.

Harden seedlings off to avoid transplant shock

Cold spells, extreme heat, wind, and heavy rain can all kill or damage young plants, so you need to wait for the right conditions before planting them outside. When the weather conditions look favourable, start to harden off your indoor-grown seedlings by placing them outdoors, in a sheltered position during the daytime but bringing them back indoors at night. Do this for 7-10 days to help them acclimatise to outdoor conditions before being permanently planted out.

Now you know how to successfully grow from seed! Don’t worry if you’ve missed the sowing window – you can still achieve a glorious garden with our wide range of plugs and potted flower plants. Like to grow your own food? Our vegetable plants will get you off to a flying start. 

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