6 plants to collect seeds from in September – and grow next year's garden for free

Our gardens might be winding down for the year, but there's never been a better time to squeeze even more potential out of it – and you can do that by collecting seeds from your plants in September.

Learning how to collect seeds is one of the most valuable gardening skills you can learn, because it means you can sow more plants for free next year. It’s also a really straightforward process – and many annuals and perennials will offer seed up freely at this time of the year.

Here’s a list of plants to collect seeds from in September to give you some budget-friendly gardening inspiration.

What you'll need

1. Alliums

Once ornamental allium flowerheads have gone brown and dry, you can start collecting seed from them – and September is the perfect time to get started.

‘Leave alliums standing in the border for as long as possible to enjoy their attractive seed heads but make sure you harvest the seed before it is shed naturally,’ advises Annelise Brilli, Thompson & Morgan’s horticultural expert.

‘Cut the heads, tip them upside down over a paper bag and shake to release the seed.’

These paper seed envelopes from Amazon are ideal, because there’s space to write key information like the variety and the date they were collected. You can start sowing allium seeds in autumn (for overwintering) or spring, or plant allium bulbs in September for a head start.

2. Poppies

September is a brilliant time to collect seeds from poppies, too. You’ll know they’re ready when the seed pods have turned a dry, light brown, and you can often hear the seeds rattling around inside when you shake them.

‘Although the hot, dry weather has made collecting perfectly dry seed a breeze, prolonged drought can also reduce both seed quantity and quality, so choose seed from the healthiest, most vigorous plants,’ notes Annelise.

‘Save the little silica gel sachets that come with packaging and place them in an airtight container alongside your paper seed envelopes to help keep the seeds dry.’

You can even buy seed boxes like this Unwins Gardeners’ Seed Storage Box from Debenhams.

3. Peas

You can also collect seeds from vegetable plants like peas in September – and after the hot summer we’ve just had, there’s a good chance that most of the pods will be ready.

My peas bolted months ago thanks to the heatwaves, but if you’ve still got a few pods left on your plants and they’ve gone dry and brittle, you can save the hardened peas inside.

‘Don’t wait until every pod is dry,’ says Helen Hutchings-Cox (@helenlikesplants), allotmenteer and GARDENA Top of the Plots Judge. ‘Once most of the pods have dried and the seeds are hard and rattling, pick them and finish drying them indoors if necessary. This reduces the risk of pods splitting and losing seed.’

4. Runner beans

Runner beans should be ready for seed collection this September, too, and the process is very similar to harvesting seed from peas.

‘Make sure the pods are fully dry before harvesting,’ says Helen. ‘If there’s still any softness or moisture in the pod or seed, give them more time to dry somewhere warm and airy. This helps prevent mould in storage.’

You can order silica gel packets from Amazon to place next to your seed envelopes if you don’t have any spares lying around.

5. Verbena

Verbena is a must if you're looking to collect seeds from perennials in September. Annelise told me that Verbena bonariensis is the species that grows best from collected seed – it’s the taller version that generally adds height to garden borders.

‘Prepare for another hot, dry summer by collecting seed from drought-tolerant favourites such as Verbena bonariensis,’ says Annelise.

‘While seed collected from named ornamental cultivars may not come true to type, seed collected from species such as this will.’

6. Ornamental grasses

You can also collect seeds from various types of ornamental grass in September to multiply your collections. Plants like maiden grass are the textural powerhouses of pots and borders, so you’ll get plenty of bang for your buck.

‘Keep an eye on grasses such as Miscanthus, Stipa and Calamagrostis as their flowerheads mature through late summer and autumn,’ says Annelise.

‘Cut well-developed heads just before the seed is fully ripe and place them in a paper bag indoors to finish ripening. Once dry, shake out the seed and store it in labelled paper packets.’

You can buy a pack of 200 paper bags for £4.99 from Amazon.

Those are just a few examples of plants you can collect seeds from in September. It's a small task for a big (and free) reward!