When, where and how to sow seeds with minimal effort

03 March 2020

We look at what you should know when you sow your seeds, whether you're planting vegetables or flowers.



Before sowing your seeds 

It's a good idea to order your seeds well in advance so you're ready for good weather. Clear out the shed, wipe down the potting table and wash the seed trays and pots so they're free from pests.

What should you sow the seeds in?

Sow your seeds into a variety of different trays, modules and pots, depending on what you have to hand and how large the plant is going to get. The pots should be plastic not terracotta pots, which dry out too quickly because the terracotta absorbs water from the soil.

Smaller plants such as lettuces, cosmos, marigolds and basil can all go into trays. Plants that are going to be more substantial and have strong roots, such as leeks, tomatoes and squashes, should be sown into modules. Herbs like parsley can go into pots.

If you're feeling thrifty look at what you have lying around that could be reused. Plastic food trays are ideal, especially the black ones which can't be recycled. Old yoghurt pots or Tetra packs cut in half with drainage holes added will also work.

You can even make seedling pots out of newspaper with a special kit, but be warned - paper and cardboard planters do tend to go moldy when they're damp for too long so they will need replacing.

Which is better pots/trays or modules?

The advantage of modules is that it keeps the roots of each seedling separate and so avoiding tangles when you come to planting out. The disadvantage of modules is that some are tricky to push the young plants out of. They work best when the roots grow enough to form a network which holds the plant plug together.

Hinged module trays known as rootrainers that allow you to remove the plant more easily are now available, but be prepared to pay quite a lot more for them compared to ordinary seed trays.

Seed trays are great for things like lettuces which are more delicate and won’t form much of a root system before planting.

Pots are good for herbs like parsley and basil as they offer the chance for the roots to travel down and establish before planting out.

What kind of compost should you use to sow seeds?

You should use a proper seed compost for sowing seeds. Ordinary garden soil will be full of weed seeds and either overly nutritious or almost inert, depending on where you live. Plus it is likely to be full of stones and other detritus which might look small to you but will be boulder-like to a seed and quite tricky to grow around.  

Do you have to sieve the compost?

If you're using a compost not designed for seeds and are instead using some lumpy home brew, yes, you definitely need to sieve the compost.

If the seeds are very small and the packet stipulates sieving, then yes.  

Otherwise just crumble up any bigger lumps with your fingers.

If you need to sieve a “bonsai” sieve which comes with interchangeable bases, each with a mesh of a different diameter, is perfect for the job.

What’s the best way to wet the soil before sowing?

Stand the soil-filled trays and pots in a large bucket or bowl or sink filled up to an inch with water (so that it doesn’t spill into the trays). By the time the water has soaked up to the top of the compost it is ready for tamping and sowing.

What is tamping?

Tamping means pressing the soil down so it is slightly compacted, and then pressing the seed lightly so the seed is touching the soil. You don’t need a specially-made gadget for doing this, the flat base of a jar or piece of wood or whatever you have to hand will do. Even the flat of the palm works. But you do need to do this or there will be too much air in the soil and your seeds won’t be snug.

Where should you put the seed trays? Do you need a greenhouse?

Not having a greenhouse or porch does make things harder. You can use small propagators but it can be a struggle as seedlings grown in mini propagators can put on growth too quickly, producing weak seedling. Putting seed trays outside under a cloche can prevent germination if it's too cold and is much more of a hassle for regular watering.

Deep, west-facing window ledges are ideal as they are warm and sunny without being scorching. Put the pots and modules on trays so you can water without splashing and leaking all over the paintwork. 

If your window ledge is not wide enough a fold out trestle table in front of a window is perfect, if you have the space. If you've got a spare room you don't use much and you could even put trays on an old, empty book shelf in front of the window, leaving enough space in front to get in and water them.

How to make sure your seeds germinate?

Check your seeds regularly, at least twice a day. Keep a water spray bottle close by to make sure the soil doesn't dry out - if it looks like it's drying out just give your trays and pots a quick squirt.

You can even reuse disposable plastic bottles by drilling fine holes in the lid to create a rose, or buying a ready-made rose adaptor for water bottles.  

How long will the seeds take to germinate?

Seed germination varies a lot. Some seeds, such as lettuces, can come up within a week. A lot of flowers, such as cosmos and marigolds, are also speedy growers. Plants such as tomatoes, squashes and leeks will probably germinate in the second week, beans can vary and it depends on the variety but towards the end of the second week or into the third is quite normal, and once they start they'll romp away.



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The material is for general information only and does not constitute investment, tax, legal, medical or other form of advice. You should not rely on this information to make (or refrain from making) any decisions. Always obtain independent, professional advice for your own particular situation.