Growing plants from seed is generally straightforward and inexpensive. It is an opportunity to increase the number of plants in your garden for free.
Seed can be saved from many trees, shrubs, perennials, aquatic plants, alpines, annuals, biennials, bulbous plants, ornamental grasses vegetables and herbs.
When to collect and store seed
Harvest your own seed is fun but takes a little understanding and planning:
- Seedheads can ripen quickly, and must be watched carefully in order to collect the seed before they are dispersed
- As a rough guide, seed is set about teo months after flowering
- Some seed is collected when well developed but immature and green, such as Anemone nemorosa, calendula and Ranunculus
- Berries need to be collected before they are taken by birds
- The plants from which you collect seed must be healthy and vigorous. This will help ensure good quality seedlings and plants
- Usually only species “come true” from seed – seedlings from a hybrid will be extremely variable
- Most seed germinates best if sown as soon as they ripen, whereas seed harvested while immature will not germinate
How to collect seed
Types of seedheads:
Seed comes in many different natural packaging. The most common forms include;
Berries (e.g. holly)
Capsules (e.g. poppy)
Catkins (e.g. birch)
Exploding seedheads (e.g. Euphorbia lathyrus)
Nuts (e.g. hazel)
Pods (e.g. sweet peas)
Winged seed (e.g. Acer, sycamore)
- Collect ripe seed on a dry day, as soon as the seedheads (e.g. capsules or pods) ripen. This is often indicated by a colour change from green to brown, black or red but before they open and shed their contents
- Pick the seedheads, either singly or on stalks, and lay them out to dry on a greenhouse bench, warm windowsill or in an airing cupboard. This enables seed to be more easily extracted from pods, cones or capsules
- If they don’t open when dry, gently crush pods and capsules to release the seed
- Collect seed from fleshy fruits and berries by mashing them in a fine sieve and then rinsing away the pulp in cold water. Leave the seed to dry for a few days on paper towels
- Exploding seedheads need checking every few days. Place a bag over them and shake – this will usually cause the ripe seedheads to explode into the bag. Alternatively, remove the seedheads on their stems as they turn brown and place in a labelled paper bag
- Nuts should be collected around the time they would naturally fall either by hand-picking or by placing a sheet at the base of the tree and shaking the branches until they fall
- After extracting the seed, clean off any surrounding material (chaff) attached to them, as this material could rot and lead to the seed damping off. Chaff can harbour moulds, pests and diseases
Some seeds (e.g. hellebore) is best sown immediately as its viability reduces with storage. However, for many species, sowing is best delayed until a more suitable time of the year such as autumn or spring so the harvested seed will need to be safely stored until sowing. Storing is also required if surplus seed as been collected. Here's how;
- Place dry seed in labelled paper packets in an airtight container with some desiccant to remove excess moisture. Suitable materials include calcium chloride (sold in DIY stores for use in dehumidifiers) or silica gel
- Excess humidity or warmth can cause seed to deteriorate or die from fungal disease or rotting
- Certain seed must not be allowed to dry out as they cannot then take up water necessary for germination. Examples are walnuts, oaks and magnolias. These seed can be stored in a plastic bag of damp vermiculite, sand, or a mix of moist coir and sand for several months
- Store in a refrigerator at 5°C (41°F) until required. Most seed will remain viable in this way for many years
Lack of collectable seed: Some plants are sterile and cannot set seed. Trying to collect seed from such plants will obviously be disappointing. Others (e.g. holly) may carry male and female flowers on separate plants so male plants will never bear seed.
Seed production can be expensive for a plant so it is also not uncommon for seed production to be cyclical – some years will be good for harvesting, others bad – or it may simply be that weather conditions for that season were not favourable, perhaps due to a late frost or drought.
Poor viability (the length of time that seed stays alive and able to germinate): If seed is sown but fails to germinate, it suggests it was not viable. Seed viability depends on the condition of the seed when first stored, how long it is stored and what seed is being kept. A good propagation book - e.g. RHS Propagating Plants Book - should be consulted.