How to grow Ash
Ash needs patience rather than skill. The embryo inside the seed isn’t fully formed at collection, so it needs a warm spell followed by a cold one before it will germinate, a process best started outdoors and left to its own devices for a year and a half. Growing ash from locally collected, healthy trees can also help support future populations with resistance to ash dieback.
At a glance
- Scientific name
- Fraxinus excelsior
- Family
- Olive (Oleaceae)
- Can seed be stored
- Yes, dries and stores
- Type of dormancy
- Moderate dormancy
- Pretreatment
- Outdoor sand plunge, 18 months
Quick links
Seasonal calendar
Year 1
Year 2
Year 3
- a Collect: Keys ripen Sep-Oct
- b Store: Pre-treated immediately
- c Treat: 18-month treatment begins
- d Treat: Full second year outside
- e Treat: Final winter before sowing
- f Sow: Worked example: collect Oct 2023 - sow spring 2025
- g Grow: Grown on until November, traditionally the start of the lifting and planting season, though this window has been shifting and shortening with a changing climate.
| Stage | Year | Month range | Note |
|---|---|---|---|
| Collect | Year 1 | September to October | Keys ripen Sep-Oct |
| Store | Year 1 | October to October | Pre-treated immediately |
| Treat | Year 1 | October to December | 18-month treatment begins |
| Treat | Year 2 | January to December | Full second year outside |
| Treat | Year 3 | January to March | Final winter before sowing |
| Sow | Year 3 | April to April | Worked example: collect Oct 2023 - sow spring 2025 |
| Grow | Year 3 | April to November | Grown on until November, traditionally the start of the lifting and planting season, though this window has been shifting and shortening with a changing climate. |
Picking
Ash ‘keys’ ripen during September and October, during which time they turn from green to brown as they dry. The most reliable seeds are those that have been picked brown. Green ash keys will grow but can prove unreliable.
Bunches of keys can be removed from branches in October, or even throughout the winter, before they are dispersed by the wind. Simply pull them gently from the tree with your fingers.
If you have picked green keys (or even those that have begun to turn brown) take care to store them in ‘breathable’ bags. They still have a high moisture content, which can cause the seeds to heat up if they don’t have adequate ventilation.
Extraction and storage
Ash keys should be separated into individual seeds. This ‘de-bunching’ process is done by hand. If you want to store your seeds for any length of time, they should be dried further in a warm place.
The extracted seeds can be stored in plastic bags, sealed and labelled in a cool, dry place (the fridge is ideal – NOT the freezer) or they can be pre-treated immediately.
Pretreatment
Before the start of pretreatment, ash seeds need to be soaked in cold water for 48 hours. The water should be changed after the first day. Drain the seeds and mix them with equal parts horticultural sand or a sand/compost mixture (for these seeds the addition of compost to the mixture is beneficial). Use 50% leafmould or peat-free compost and 50% horticultural sand. For each handful of seeds add two or three handfuls of mixture. Select a pot that has enough room for this seed/sand mixture (and a bit more) and put a layer of stones in the bottom. Cover the stones with sand. Place the seed/sand mixture on top of this and cover this with 2-3cm sand. Label the pot and stand in a shady spot outdoors.
The pot needs to remain outside for eighteen months. This is where patience is required! Water the pots if they show signs of drying out and protect from birds and mice if they discover your seeds. We will be sowing the seeds the second spring following collection. Freshly collected ash seed does not contain a fully- developed embryo (young plant). It needs a full summer (warm temperatures) for the embryo to grow to its full size and be ready to germinate.
Sowing
After the seeds have spent a whole summer and the following winter outside, they are ready to be sown (eg. collect October 2023 and sow spring 2025).
Sow three seeds per pot or aim for about 400 seeds in one square metre of a seedbed. Cover the seed with 5-10mm of coarse horticultural grit. Firm the seeds.
Growing
After the seeds have spent a whole summer and the following winter outside, they are ready to be sown (eg. collect October 2023 and sow spring 2025).
Sow three seeds per pot or aim for about 400 seeds in one square metre of a seedbed. Cover the seed with 5-10mm of coarse horticultural grit. Firm the seeds.
Ash will grow quickly when supplied adequately with water. Ensure the young seedlings are kept moist. Reduce watering a little towards late summer.
Planting your new tree(s)
When your Ash is tall enough, it can be planted into its new home. Prepare the site well by clearing away any weeds or grass and make a hole big enough to accommodate the root ball. Plant carefully in the hole, to the same depth as it was in the pot or ground, and firm back the soil. More tree planting details here.
