Home Propagation Sowing seeds

Sowing seeds

Sowing, pricking out, hardening off

Growing from seed is incredibly rewarding, so why not give it a go? It’s also one of the cheapest methods of getting new plants, so there’s little to lose if you forget to water them. Follow these simple steps to give you the best chance of success.


Clean and disinfect pots, propagators, tools

dirty pots, trays and propagators
In need of a good clean – dirty pots, trays and propagators

Firstly, make sure your utensils are clean if they have been used before. A good scrubbing with hot soapy water will do but I always use Citrox to clean my propagators, seed, gravel trays and pots.

Citrox is a citrus-based garden disinfectant – harmless to plants, but it treats fungal/bacterial problems. Soak pots, etc, for 10 minutes then give them a good clean. Spray and wash all larger surface, like propagator covers.

Citrox is very good at keeping capillary matting (used in trays/propagators as an aid to watering) ‘unsullied’ by nasties – douse it with a dilute solution once a month. You can also use it to disinfect bird tables and keep water butts ‘sweet’.

I use my capillary matting white side up – it reflects more light early in the season. Later on, it doesn’t matter.


 Follow the packet instructions

nasturtium Milkmaid
Foolish self-seeded nasturtium Milkmaid succumbed to frost, November 30, 2014 – it wouldn’t be told

It’s amazing how many people don’t. If you’re new at this, wait until at least mid-March when the light intensity is better if you’re sowing on a windowsill.

Wait even longer if sowing direct into soil outdoors (it has to feel warm to the touch and not waterlogged – seeds will rot in cold, wet soil).

Follow instructions for the temperature of germination, etc and when to water – some people do this before the seeds go in, some after. It doesn’t matter with big seeds, but tiny ones get washed into corners.

Runner bean Moonlight
Runner bean Moonlight makes an appearance in late April

Sowing depth, if you look for a general rule on the internet is confusing – one-and-a-half times the length, twice the length, four times the width… the conflicting advice goes on.

It’s true some seeds need light to germinate, so don’t cover them at all, but what’s the real answer?If you have no packet and the seeds are small, cover them lightly. Obviously, beans and peas need to be much deeper

Again, follow the seedsman’s (or seedswoman’s) instructions. If they don’t come up, complain and you’ll get some free seeds.


Potted guide: How do I sow? In what container?potted-guide-logo

You’ll see terms like:

  • Broadcast – chucking seeds randomly over the soil outside;
  • Drills – small furrows you sow the seeds into, then cover them over;
  • Thinly – means what it says – don’t plant them in a clump, or you’ll make life difficult. Sowing thinly means less thinning out (see below).
  • Station sow – nothing to do with trains. This term is used for things like beans, peas, and sweet peas when sowing outside straight into the ground where they are to grow. Often two are sown together and the weakest is sacrificed. Gardening’s tough, get over it.

    Broad bean Super Aquadulce
    Broad bean Super Aquadulce
  • Modules – sometimes you can sow directly outdoors or in modules indoors. These are seed tray inserts divided up into little cells – plant one or two seeds in each. They’re a good idea if you live in the North or have cold/clay soil that takes ages to warm up in spring.
  • Packets usually give instructions telling what container to use. Don’t go overboard – they’ll only be in this for three-four weeks in seed compost, which is low nutrient and expensive, which brings us to the next stage…

Pricking out time

Aquilegia Green Apples
Pricking out Aquilegia Green Apples

Pricking out seedlings is a job you either love or hate. To make it less of a chore, get comfortable and sit down.

Most of us sow seeds (especially small ones) in trays. It’s economical, as seed compost is expensive, and you don’t have to sow the whole packet.

Once the seedlings have developed true leaves, things start to get crowded. They can become leggy and can fall victim to ‘damping off’ disease.

As soon as they are big enough to manage, move them into modules, filled with decent multipurpose compost.

Lift up a chunk of the seedlings with an old teaspoon and, holding a seed leaf (never the stem), tease out individual plants from the mass.

Dahlia Bishops Children
Dahlia Bishops Children being pricked out

Choose only the ones with the most vigorous root systems to be potted on.

Make a hole in the compost with a dibber and gently ease the roots into the hole, then gently backfill in.

If the seedlings are more spaced out and have bigger root systems, half-fill the modules, place the seedling in and fill around with compost.

Water in gently with a small watering can. Don’t be alarmed if some seedlings topple over – they need to settle in the soil. Gently firm them back in.

Keep them out of direct sunlight or rapidly fluctuating temperatures for a few days and keep well watered.

Depending on how long it is until your last frost, you may have to pot them on again before it’s time for them to go outside.


Hardening off

One of the problems with starting plants off under glass is that they need to be hardened off.

Hardening off plants
Shabby-looking lean-to for hardening off plants

Even hardy plants get used to regular watering, still air, and stable temperatures. Putting them outside to survive in widely fluctuating temperatures, much stronger sunlight, and winds will lead to a check in growth, even death if they are caught by frost.

The effect of hardening off is to thicken and alter the plant’s leaf structure and increase leaf waxiness. It ensures new growth is sturdy although much slower.

Sweet peas hardening off in an empty Belfast sink
Sweet peas hardening off in an empty Belfast sink – trust me, they’re under there

You need to harden off gradually, over a couple of weeks, depending on the weather. On a mild day, start with 2-3 hours of sun in a sheltered location.

Protect seedlings from strong sun, wind, hard rain and cool temperatures. Hardy plants acclimatise faster than tender kinds.

Don’t plant out tender plants before the date of the last frost, which is usually the end of May/beginning of June in NE England – but have horticultural fleece ready.

If you don’t have a cold frame, place plants in a sheltered position in front of a south-facing wall or hedge and cover with fleece to prevent sun scorch and temperature shock.

Plants hardening off at the end of May
Plants hardening off at the end of May

I made a small lean-to out of poles and bubble wrap – it’s not pretty, but it does the job. It’s also sheltered against a west-facing wall, which slowly releases its heat at night.

For the first week, leave outside during the day, but bring in at night. In the second week, leave outside at night, but keep covered (unless there’s a frost forecast).

Towards the end of the fortnight, remove the bubble wrap during the day. If the weather is suitable, leave the plants outside at night but ensure they are covered. After this, leave them uncovered before planting out.

Covering with an old curtain or extra fleece can protect from sudden sharp night frosts.