How to grow Field Maple
Field maple keys need both a warm spell and a cold one before they’ll grow, unless you collect them slightly green rather than fully ripe and brown, in which case no pretreatment is needed at all and you can sow them straight away.
At a glance
- Scientific name
- Acer campestre
- Family
- Soapberry (Sapindaceae)
- Can seed be stored
- Yes, dries and stores
- Type of dormancy
- Moderate dormancy
- Pretreatment
- Outdoor sand plunge, 18 months (none needed if collected green)
Quick links
Seasonal calendar
Year 1
Year 2
Year 3
- a Collect: Green-harvest late Aug, or brown Sept-Oct
- b Store: ASAP after collection
- c Treat: 18-month treatment (Cold/Warm meta itself empty)
- d Treat: Full second year
- e Treat: Final winter
- f Sow: Second spring following collection
- 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 | August to October | Green-harvest late Aug, or brown Sept-Oct |
| Store | Year 1 | October to October | ASAP after collection |
| Treat | Year 1 | October to December | 18-month treatment (Cold/Warm meta itself empty) |
| Treat | Year 2 | January to December | Full second year |
| Treat | Year 3 | January to February | Final winter |
| Sow | Year 3 | March to March | Second spring following collection |
| 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
The small winged seeds of field maple can be collected during September and October when they have turned brown but before they are dispersed by the wind. At this point they have developed additional dormancy which needs more patience to overcome.
If you harvest the seed while it’s still flushed green (not yet brown, but mature, in late August or very early September), you can avoid the need for more patience – although growing trees will always need some patience!
Collect the seeds in cotton or hessian bags if you can. If they are left in plastic bags, they may sweat and heat up as they have a high moisture content. This can damage the seed.
Extraction and storage
Lay the bunches of seeds out in thin layers somewhere dry at room temperature as soon as you can after collection.
As the seeds dry a little, the bunches will begin to break apart. You can gently help them along the way.
Your extracted and dried seeds can be stored in plastic bags, sealed and labelled in a cool, dry place (the fridge is ideal – NOT the freezer).
Pretreatment
If you collected the seeds slightly green, no pre-treatment should be needed and you can move straight to sowing or store them over the winter to sow in spring.
For the fully ripe and brown seeds, soak them 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). 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 that patience is required! Water the pots if they show signs of drying out and protect from birds and mice if they discover your seeds.
You will be sowing the seeds the second spring following collection.
Sowing
Aim to sow during March on seedbeds or in pots. If you have stored green seeds over winter, it is a good idea to soak them for 24 to 48 hours in cold water before sowing.
Cover the seeds with 10mm of coarse horticultural sand, grit or compost. Firm the seeds gently.
Growing
Field maple will grow fast in good growing conditions.
It would not be unreasonable to expect up to 60cm growth in the first year, but the plants can be transplanted or left in the pots (repotting if necessary) for another year. Plants in pots will need to be fed regularly whilst they are actively growing (April-September).
Field maple 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 Field maple 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.
