Monday, September 26, 2022
HomeGarden designLearn how to Sow Seeds Indoors | Plews Gardening Classes

Learn how to Sow Seeds Indoors | Plews Gardening Classes

Learn how to sow seeds indoors will get right down to the nitty, horticultural gritty of sowing, as promised within the earlier Plews weblog, Sowing Seeds Indoors (hyperlink is beneath).

That weblog lined what you want and what you don’t in the best way of sundries and tools. Gadgets you could possibly recycle and ones you could possibly purchase.

This time we need to sow the seeds themselves. There’s additionally a video on the finish demonstrating find out how to sow differing kinds and sizes of seed.

Indoor seed sowing is not only about the place you might be standing when sowing, however the place the seed trays and pots shall be till the seeds have germinated and on the very least, be sufficiently big to transplant. Indoors includes greenhouses, polytunnels, cold frames, windowsills. Basically anywhere where you can give the newly sown seeds protection from the elements.


How to Sow Seeds Indoors – Growing media

The presumption is that you will not be growing hydroponically but using a more traditional growing media.

NB there are real health and safety reasons why you should not just wear gloves when handling soil, compost, etc but also be in a well ventilated space.

This is generally referred to as ‘compost’ or seed compost. Which can be confusing as ‘compost’ is the stuff made in compost bins and used to improve soil quality and offer up nutrients to give healthy plants. So I’ll call it growing media to save confusion.

What it isn’t, is garden soil. Whilst you can use garden soil indoors, because conditions and seed requirements are different, it’s not always the best choice. Part of this relates to the type of soil you have in your garden borders. For example a clay soil is slow to warm up in spring and can be extremely wet. Neither of these qualities are what seeds are ideally looking for. Mixing your garden soil with other ingredients, may help resolve some of the problem (see making your own seed compost below).

The growing media needed for sowing seeds doesn’t require much compost in its mix. Seeds within their shells have most of the nutrients they need for their initial growth. It’s more important to ensure that they don’t rot, so a growing media for seeds should be free draining.

You could use John Innes No 1, sometimes called seed compost. This is a tried & tested seed compost mix not a brand and is now available as peat-free. If the seed compost seems more generic check the bag for what is in it. Avoid those which have peat in them, unless it happens to be Moorland gold. This compost is made with ‘naturally filtrated peat’ that would otherwise be washed to the sea.


Gardening Teacher Tip

Are you concerned about how to sow seeds indoors when the plants they grow into need acid soil and your growing media is peat free?

Its okay. The seeds will generally be fine, its more about the seedlings that germinate. Most will manage as multipurpose potting compost is usually a neutral pH. And you can add sand to the mix which will help as this is acidic.

However, if you know about the acid loving plant seeds in advance, you could get some peat free ericaceous potting compost and mix grit in with it for drainage. Then the seedlings will also be fine until they’re large enough to transplant.

heather, daffodils, narcissus, spring flowering bulb, small perennial shrub


How to Sow Seeds Indoors – Make Your Own Seed Compost

Yes, you could make and mix your own growing media! To be effective, seed starting soil needs to be lightweight and drain extremely well. Nutrients are less critical until the seed has germinated. But as you won’t be transplanting as soon as that occurs, its best to include some nutrients into the mix.

Which elements you add is your choice but choose one from each column

2 parts 1 parts 1 parts
peat free multipurpose


horticultural sand

horticultural grit



horticultural sand

horticultural grit



garden soil


enriched multipurpose

peat free multipurpose


horticultural sand

horticultural grit



coir enriched multipurpose

peat free multipurpose

horticultural sand

horticultural grit



garden compost

soil improver

enriched multipurpose

horticultural sand

horticultural grit



horticultural sand

horticultural grit




  • Smaller seeds especially need a fine seed compost, so be prepared to sieve coarse material and clumps. (Rubbing out large clumps with your gloved hands is okay!)
  • Coir will open up a mix but may be too coarse for smaller seeds. It has no or very little nutritional value
  • There are pros and cons about using garden soil, too many to discuss here. But I will suggest that clean soil could be considered an important factor.

For most seeds the ratio will be 2:1:1 (top row)For seeds that have a tendency to rot, or if you feel overwatering or a damp environment could be an issue, amend to 2:1:1.5

It doesn’t matter what scoop or jug you use to measure, so long as you use the same one for each. Mix ingredients together thoroughly. An uneven seed compost could lead to various issues, such as crowding and damping off.


perlite, vermiculite and horticultural grit, growing media, propagation

perlite, vermiculite and horticultural grit

Seed Trays vs Modules and Pots

The question here is whether your seedlings can tolerate being transplanted (moved) from seed tray to a pot as a seedling. Or from seed tray straight outside as a larger seedling.

If that’s a yes, they can cope with some root disturbance, then you can use seed trays. But if it’s a no then you’ll need to sow the seeds in separate modules or pots.

There is another matter to consider and that is are the seeds pea or bean family members? Legumes or Fabaceae, including sweet pea flowers need a long root run and do best in tall pots or deep trays. They do best in these as their long roots can go down rather than across – it makes them more stable when you transplant outside.

For re-using and making your own pots, see blog links below.

How to sow seeds indoors – the size of seeds

Most seeds need light, air (oxygen) water and warmth to germinate. Basically, keep the growing media warm and damp, but not too damp. Then you can look forward to seeing those little green shoots which mean germination has occurred.

However, sometimes getting a better germination rate from your seeds starts with treating them in different way depending on their size.

lavender seeds,hans brameier on pixabay

Tiny seeds

Tiny seeds are easier to sow if you mix in a little fine sand with the seed. Then you can see how they’re distributed across the soil surface – in clumps or spaced out.
Sprinkling them from the packet may not be precise enough. I find that tipping a few onto my palm and using the lines on my hand to direct the seeds onto the surface of the compost works better.
Leave tiny seeds uncovered, or with only a shallow layer of grit, vermiculite or fine sand. This allows air & water to easily reach more delicate seeds.

nasturtium seeds, hans brameier on pixabay

Larger seeds

Rounded medium-large seeds  include the onion family. These are easy to handle and sow in trays.  Larger seeds such as sweet peas and beans can be placed in cells individually, or in twos or threes depending on the size of pot.


Large flat seeds

Such as those in the squash family and sunflowers. These benefit from being sown on their narrow sides in pots so that they don’t rot. Gently push them in and cover with more growing media.

sowing squash seeds - wrong     wrong


sowing squash seeds - right



How to sow seeds indoors video – takes you to our YouTube channel

Read on if you prefer text and still pictures


How to Sow Seeds Indoors

Ready, steady, sow!

Get your seed tray ready; fill with growing media nearly to the top and give the whole thing a gentle shake to level the soil. Tap down lightly on the surface with another seed tray to get rid of any air pockets and give yourself a smooth surface.

Larger seeds can be held in your fingers and spaced out in the seed tray. Remember to allow enough room for each seed to germinate and develop roots as well as a shoot. They need to get to the first true leaves before being large enough to transplant. A zig zag pattern gives the optimum spacing.

sowing-seeds-in-diagonal-pattern -gardening lessons - propagation

If you’re sowing seeds into modules, have 1 -3 seeds per module.

For smaller seeds, you may find it easier to sow them in straight lines so you know where they should be. Tap your hand gently to get an even flow of seeds. If they don’t come out evenly, don’t worry too much. It may just be that you will have to thin them out after germination.

Place in a gravel tray (like a seed tray but without holes) so water is contained. Sprinkle over a layer of the growing media sufficient to cover the larger seeds. Leave the small ones uncovered.  Water with a gentle spray. Add a clear lid if required for extra protection or moisture retention.

watering-in-seeds - gardening lessons -propagation


How to Sow Seeds Indoors – Keeping a Record

You may feel that labels are sufficient, and they may well be. But it doesn’t harm to also have a simple list of which seeds you sowed on a particular day. If nothing else it enables you to quickly check if they should be germinating. Germination can be 5 days to 2 weeks or longer, depending on the seeds.

And for the next stage – keeping your seedling healthy – we head to another blog!


and finally

Hopefully I’ve helped you with tips for how to sow seeds indoors. If  the blog links and videos leave you hungry for more, you may like to consider a Plews Gardening Course, where we enjoy 1-2-1 practical sessions in your own garden. A mix of practical and theory (the “why we do things”) bespoke to you, your garden and what you want to learn. And we can transplant some of the sessions into 1-2-1 zoom calls.

For further gardening advice and inspiration, check out Plews Potting Shed blogs, including the selection below, and our monthly Tipsheet  – You could come and find us on Instagram  Pinterest and Facebook too.


Related Gardening articles you may enjoy from our Award Winning Blog

Sowing Seeds Indoors – what you need and what you don’t
Peat free compost – are you still confused?
10 Tips for Saving on Garden Essentials
What Might a Plews Gardening Lesson Be Like?
Ten tips for Successful Seed Shopping

Plews eBooks

“Compost and Composting”

“In Your Spring Garden”

seed sowing stuff




Please enter your comment!
Please enter your name here

Most Popular

Recent Comments