Growing trees from seed
Setting up a Small Tree Nursery.
Setting up a mini tree nursery, whether in your back garden or on a window sill, is a particularly interesting and rewarding pastime. Before you start, decide how much time and space you want to dedicate to the project. Your nursery may initially be a few flower pots or seed trays, a section of vegetable plot or flower bed, or in a prepared seed bed.
Small Scale Tree Rearing
1. Just a few trees
Most people start on a small scale – even a yoghurt pot on a window sill. You need some simple pots, preferably with small holes for drainage or a seed tray. The soil should be free-draining; most garden soil is improved by mixing in sand and compost or leaf mould, or you can buy potting compost. (Please avoid peat based composts).
Fill your pots with compost and sow a few seeds not too deep (see advice for each species). Keep them sheltered, not too hot or cold, and remember to water them on a regular basis.
Once the seeds germinate, keep watering and weed carefully once you are sure which are weeds and which are young trees!
After a few months, the trees will outgrow their pots and will need more space and depth for their roots. At that stage you will need to plant them out into a prepared bed or into larger pots/containers.
The young trees could even be moved into cleared ground at their final site, so long as the young plants will be looked after – weeded, watered and protected from being eaten. This is good for species such as holly, blackthorn and gorse, which are not very successful when transplanted as larger seedlings.
If your aim is to produce relatively small numbers of good young trees, and you have access to a cool greenhouse or poly tunnel, here are two good systems.
2. A tried and tested system – BTCV
Rootrainers. These are moulded plastic pots or cells which come four or five to the set, or ‘book’. Because the books are hinged and can be opened out, it is possible to observe soil condition and root systems without harming the seedlings and to remove the plants easily when they are ready. The lengthwise grooves in each cell promote straight root development. They range in size from 8- 20cm in depth and 65-350ml in volume; a I 1000ml-volume cell is now also available.
Rootrainers arrive flat and opened out. They should be closed and placed in 36×2lx9cm trays ready for filling and sowing. The number of books per tray varies between 8 and 14.
3. Another good way – Neville McKee
Collect your seeds stratify as necessary (see advice for each species) and sow in shallow seed trays using a peat substitute potting compost.
Once these have germinated and grown a little, pick out individual seedlings – handle with care, preferably lifting them by the cotyledons, the first green ‘leaves’ – and transplant into plug trays (available from garden suppliers) one seedling in each plug section.
Keep the seed trays and plug trays in your unheated greenhouse or poly tunnel.
In summer, the entire plug plus seedling should be tipped out – gently – and planted outside into a prepared bed. The seedlings will be ready for their final planting just one year later, and in some cases even that first autumn. The use of plug trays seems to give seedlings a really good fast growing start.
4. Plant ‘on the spot’.
There is one more option, which is that seed may be sown directly on the site where you want your final tree or bush. This avoids any problem with moving young plants. Prepare the site as you would any seed bed and plant several seeds – this should ensure that at least one germinates successfully. Later you can select out the best young plant to grow on, and move the others.
Remember to put in a marker and ideally cover the sites with wire or other mesh to mark and protect it. Keep watering – don’t forget about your tiny seedlings!
Larger Scale Tree Rearing.
If you have suitable land, and enough time and energy. you may consider a full scale tree nursery. Even a small nursery can yield hundreds of trees each year.
Choosing the Site
When choosing the site, keep in mind these important factors.
- The site should not be waterlogged – a raised bed with coarse grit incorporated in the soil will provide adequate drainage.
- Water will be required for summer watering.
- Shelter is needed from the morning sun and strong wind on frozen foliage. Do not use an east facing slope.
- Protection against morning sun on dewy leaves is essential as the scorch can kill seedlings.
- Protection from dogs, children, footballs and rabbits. If a rabbit proof fence is required use a 31 mm gauge wire and bury the bottom 30 cm under ground level.
Site Preparation.
Preparation of the site can be the most time consuming part of growing trees from seed, but it is absolutely worthwhile. The better the site preparation, the better the germination and growth of young trees.
Once the site has been selected, it must be cleared of grass and weeds. Remove the grass by paring away the top three inches of soil and grass roots. Stack these shallow sods off to the side as next year this will be a fine compost for a seed bed.
Perennial weeds such as dandelion and dock must be removed from the soil, otherwise they will grow up through your seedlings, smothering and starving them.
Dig over the soil to a minimum depth of 25 cm, removing larger stones and weed roots. If this is done in the autumn the winter frost will break up the soil further. Should the soil be heavy and sticky, dig in some sharp sand or grit. This will aid drainage and render the soil more workable.
If the soil is sandy incorporate well rotted old manure or compost to give a firmer texture and help it retain moisture. With the site selected, fenced and dug over, the next stage is the growing beds. This is simply soil raised to approx. 10 cm above ground level, flat topped, about 1m wide and as long as your enclosure allows. Be sure to leave a narrow path around each raised bed for easy access and weeding.
Shape the bed by putting a string line where you want the edge of the bed to be. Cut a flat bottomed channel down one side of the line and deposit the soil on the opposite side of the line. A path has just been created! Shape the bed. Level the soil.
Walk over the surface of the bed on your heels, or roll it, then rake the bed’s surface.
Repeat this process until the surface is firm and fine. This will ensure the bed does not sink and sag due to there being air pockets present. You are now ready to plant seed.
If the bed is made earlier in the season, weeds can be eliminated before sowing in the autumn or spring. Some nurseries use herbicide and/or soil pesticides.
Planting Seed
Dibbling
Hazel, beech, oak and chestnut are suitable for this method. Large seed can be planted by piercing a hole, with a round nosed dibber, twice the depth of the seed.
Drop the seed into the hole and cover with sieved sand or soil. Firmly, compact the medium to eliminate air pockets.
Broadcasting
Small seeds are planted in a similar manner to grass seed, i.e. scattered evenly by hand on the surface of the seed bed.
This is then followed by rolling the bed and covering the seed with 2mm sand.
Birch is sometimes uncovered as it is light sensitive. Treat stratified seed in the same way. as seed sown fresh.
If weeds appear on the seed bed gently remove them by snipping or slicing the root under the soil surface with a sharp knife. If you have any doubts as to whether it is a weed or a tree postpone weeding!
Protection
Seeds and seedlings are vulnerable to being eaten. In the seed bed they can be protected by erecting a frame over the lines of seeds/ seedlings.
Small mesh wire netting may be used or better still a fabric mesh such as Mallardworth black lin. stretch netting.
This can be spread over wire hoops well down into the ground and pinned down at the sides with short stakes.
It is necessary to have a good seal at the side and ends of the rows, especially if mice are your problem!
Lining Out
After one year in the seed bed, the small tree seedlings will have grown substantially.
They will appear crowded, especially if they have grown from small seeds which were originally broadcast quite thickly.
It is necessary to move them on to the transplant bed, prepared and weeded as recommended in ‘site preparation’. The little tree seedlings should be lifted gently from the seedbed without damaging the roots, and transferred as quickly as possible to their new area. If they have to be left for a short time, cover the roots – damp newspaper is a good idea.
Make a hole with a ‘dibber’ for each seedling, place it gently in the hole and press soil around to the same level as it was growing before – too deep or too shallow will check growth and may even cause the young tree to fail. Plant in a straight row and leave regular spaces of about 30cm. between seedlings – which will make clear why this process of planting on is known as ‘lining out’.
If the seeds were originally sown well spaced out – acorns, for example – the tree seedlings may be left for two years in the seed bed and then lined out.
The transfer of tree seedlings is normally carried out in the autumn and winter, not in spring when they are actively growing and even more vulnerable to disturbance.
There is one exception – holly seedlings actually like to be moved in the summer, when the soil has warmed up!
Root Pruning
When tree seedlings have been grown under crowded conditions in the seed bed, their root systems may be too ‘up and down’ and not sufficiently all-round. To encourage bushy root growth, which leads to a healthier and more stable tree in the long term, young seedlings may be ‘root pruned’.
Root pruning is carried out when the young seedling is lifted from the seed bed. The roots are trimmed, using large scissors or secateurs, just cutting across the largest roots so that the tree is left with a more even length of main roots. This encourages the cut roots to send out side roots, in the same way that a cut branch abrove ground will send out side shoots.
In commercial forestry nurseries the young tree seedlings have their roots pruned by a cutter bar when they are still in place in the seed bed. On a smaller scale, we can lift and trim roots of a small bunch of tree seedlings held together, but you may wish to carry out a precision job on each individual seedling – it is up to you how much time you wish to spend on this task.
Root pruning is not necessary for seedlings which have been grown in individual pots or plug trays, but is does assist seedlings grown on a larger nursery scale to make good growth subsequently. The result is a large root surface and a comparatively small shoot. This favourable root/shoot ratio is ideal for transplants. It may look severe but it is for their own good in the end!
Looking after your Seedlings.
Attention must be paid to their general state of development. Check for mildew and aphid infestation regularly, and use chemicals if you need to. Oak and Hawthorn are especially vulnerable to grey leaf mould infections.
Water beds if it has not been raining for a few days. (Daily for birch -when very young).
In the autumn defoliation occurs and dormancy commences. This is the time to transplant seedlings -gently.
At the base of each seedling there is a colour difference. This is the planting depth for each seedling.
If planted too deep the seedling will die.
Dibber or trowel planting is used at this stage. Do not “corkscrew” the roots into the hole or the tree roots will become twisted and distorted.
The planting season generally finishes at the end of March. Seedlings can be moved at other times if they are re-planted rapidly without the fine roots drying out.