If you’re growing trees from seed, it’s worth trying a couple of different methods. Using plastic reusable cell modules for medium sized seeds and nuts is a good idea – you can look after them and water them easily in a garden and they’re generally ready to plant out after just a single season. But for seeds that you’re going to collect and plant in larger numbers – like birch, alder, ash or field maple – it’s worth making a seed bed and sowing them like you would lettuces or carrots. Seed beds are great if you want to start a community or school tree nursery project.
First, find a good, flat, sunny spot and decide what size you want – in this series of images I’ve gone for 6ft by 4ft. I’ve cut around the edge of my measured rectangle with a spade, then cut and lifted the turves and laid them face down, to suppress weeds and prevent drainage issues. Now, I hammer a sharpened stake (from my local fencing supplier) into each corner. I place a board (from the same supplier, but I’ve recycled from an earlier project) against each side, then mark and saw it. You could make a more robust and visually nicer bed with railways sleepers, but they’re more expensive. I clamp the boards in position before I screw them in, to make it easier.
Time to get some seeds. Its early September, and my birch tree seed cones are just starting to go brown. I pick a few off a few different trees and collect them in a paper bag. You’ll see that when you rub the cones between your fingers they collapse and you get hundreds of seeds. You also get the little bird’s foot bracts, but they’re not worth separating out. I’m going to sow a thousand or so, just to see what happens.
I part-fill the bed with soil-based compost, ideally mixing in some well-rotted leaf mould (good for microscopic fungi and nutrients). I then shake the seeds over the bed and cover them with a sprinkling of sharp sand (available from any builder’s merchant or DIY store). This is to stop them blowing away and it suppresses weeds. Finally, I cover the bed with a wire mesh to prevent birds (and badgers) getting at the seeds; now I’ll leave it until spring and see what happens.
What applies for birch also applies for the cones of alders. For maples and ash the process is similar, but you can add more layers of soil, then seeds, then sharp sand. Incidentally, you’ll see that I’ve inserted some cut-down old tree protectors. I’m going to sow hazelnuts and acorns in these as they ripen – about the end of September or early october. The tubes will protect them and they’ll be easier to lift individually without rooting into each other. The birch, as they grow, will get thinned and either potted on or left to pull next autumn for planting in their final location.
I’ll be making another bed soon, for when the field maple seeds are ripe. Apart from being a wonderful tree in its own right, field maple makes excellent hedging; and for that you need a lot of plants.