Start collecting seeds now from your spent garden plants and not only will you save money on increasing your stock, but you may well end up with some rather surprising results.

Seeds collected from garden plants may not produce seedlings identical to the parent plant, as they are open pollinated by the wind or insects, without human intervention. This means although the seedlings are likely to share most of the same characteristics, you may sometimes end up cultivating some interesting or unusual plants.

Heather Cooke, seed team leader at RHS Garden Wisley, offers the following tips on collecting seeds…

Know what you’re looking for

Do some research to make sure you know what to look for and where to find the seeds on each kind of plant. Types of seed ‘packaging’ include berries (holly), capsules (poppy), catkins (birch), cones (pine), exploding seedheads (Euphorbia lathyris), nuts (hazel), pods (sweet peas) or winged seed (acer, sycamore).

When to harvest

Harvest seeds when they are ripe but before they are dispersed naturally, which is in late summer or early autumn for most popular summer-flowering plants. As a rough guide, most plants set seed around two months after flowering.

Plants disperse their seed in different ways. The seeds of many grasses and trees are wind-dispersed, while others, such as euphorbias, geraniums and violas, have explosive pods, so you will need to collect from these plants just before the pods open.

Look for changing colour

To tell when seeds are ripe, look out for seed pods changing colour (often from green to brown), seedheads starting to split or changes in seed colour. Usually, the seed is dark and hard when mature.

Berries are usually ripe for seed harvesting when birds or squirrels start to eat them, so you need to be quick before they eat them all.

Choose the best weather conditions

Pick a calm, dry day to harvest your seeds, as a strong breeze can make it difficult to collect them from plants that are blowing around and seeds that get wet may rot.

Know how to extract the seeds

Ripe seed pods can either be cut off (taking care not to tip the seed out), or shaken directly into a bag. With some seed heads, the seed can be stroked out (astrantia, scabious and amaranthus, for example).

Protect yourself

Wear protective gloves around plants that are poisonous, such as monkshood (aconitum) or foxgloves, or those with an irritant sap, such as euphorbias. The same applies to really prickly plants and those with dusty hairs or a dusty bloom, such as primula or echium.

Drying out seeds

Dry them in open cardboard boxes lined with paper, which helps air the seeds, dries them out and stops them from going mouldy. Boxes should be kept cool and dry for a couple of weeks.

Clean them up

When the seeds are dry, remove excess plant material or chaff to minimise the spread of pests and diseases. Use tweezers to remove any big pieces of unwanted material, before carefully blowing over the seed, or gently shaking through a fine sieve to remove any remaining chaff.

For berries and fruits, squash them in a sieve and wash the fleshy coating away with water, before drying the remaining seeds on blotting paper or a paper towel. Once dry, pick over with tweezers to remove any remaining plant material.

Store them carefully

Don’t use plastic bags to store seeds, as these will trap moisture and can cause seed to rot. Use paper bags or envelopes instead, and label them with the name of the plant and the date the seed has been collected – fresh seed germinates better, so each year when you collect new seed you can throw out any older packets.

Once seed is clean, dry and packed, store the packets in an airtight container in the fridge. Keep sachets of silica gel from new shoes and handbags (or alternatively a small handful of rice) to add to the container, as these will absorb any moisture.

How long will they keep?

If properly stored in a cool and dry environment, some seed can remain viable for years, but in general, fresher seed has a better rate of germination.

Some seeds, such as hellebore, should be sown immediately after harvesting, as they don’t keep well and are less likely to germinate after storage. But many species are better sown at a more suitable time of year, such as spring, and storing is also necessary if you have collected more seed than you can use at one time.

And future germination?

Some take longer than others, and some require special treatment to germinate. Seeds with a hard coat, such as sweet peas, may need to be nicked or soaked to help them germinate.

Others with very small seeds, such as tobacco plants (nicotiana) and foxgloves, may need light to germinate, in which case they should be sown on to the surface of a prepared seed tray of compost.