Tree Seeding Trials
Direct sowing of seeds into the ground could be an effective way of establishing certain tree species in new woodland planting schemes. However, experience has shown that this is only likely to be successful when growing large seeded trees such as oaks, chestnuts and hazel.
Oaks grow very easily from acorns. They germinate as soon as they drop from the tree. Could this be a cheap and effective way of establishing an oakwood or enhancing a rewilding site? On cultivated ground in my tree nursery I have tried dropping acorns and chestnuts into 60cm Easywrap guards and covering with a handful of soil. Results were encouraging, particularly for acorns, chestnuts were more likely to rot over Winter, but results were still good.
In November 2020 I set up a trial in a newly drilled field of winter wheat. 100 90cm canes (12-14lb/100) were pushed into the ground 1 metre apart in a 10 metre by 10 metre grid. 100 60cm Easywrap guards were placed over the canes and pushed 2cm into the cultivated ground. A single acorn was dropped into each guard, followed by a handful of potting compost.
Over the Winter, about 10 of the canes were knocked over by marauding deer. These were replaced as necessary.
The trial finished at the end of June 2021. Guards and canes were removed for reuse and the growth of the acorns assessed. 41 acorns had produced shoots from 5-20cm tall. The remaining acorns had either failed to germinate or had produced curly roots that were unable to penetrate the mineral soil.
The poor germination could be traced back to the Spring weather. April 2021 was very dry and cold with frosts nearly every night. The acorns were slow to grow. By the time they did grow the compost was totally dry and fluffy. The growing root had simply pushed the acorn around.
Next time round the acorns will be sown as soon as possible and covered with a handful of soil rather than compost. A warm and wet April would also be good.
In November 2021 we tried direct seeding Sweet Chestnut, Castanea sativa. This time we used a wider shelter to accommodate the larger chestnut leaves. 100 60cm green tinted Defender tree shelters were erected and pushed into a seed bed on the tree nursery. A single chestnut dropped into the shelter was followed by a handful of nursery soil. The results were interesting. 75 of the chestnuts germinated, 25 had rotted, probably due to over irrigation. By Autumn only 5 had reached the top of the 60cm tall shelter. Growth inside the shelter was spindly with flaccid, weak leaves, but as soon as the chestnuts emerged out of the shelter they developed strong, healthy leaves.
It appears that the green tinted shelters inhibit photosynthesis in the young plant. This is not much of a problem when planting a 40cm chestnut into a 60cm shelter – the plant has food reserves and can soon grow out into the sunlight. It is however critical for the seed to have sunlight of the correct wavelength as it emerges from the ground and begins to photosynthesise. In future I would recommend using clear shelters.
In summary I would suggest that direct seeding is a cost effective way of establishing oak and sweet chestnuts seedlings in new woodland planting schemes. Acorns cannot be stored for more than 6 months, so a poor mast year generally means that 1 year oak seedlings suitable for planting will be in short supply the following year. If there is a good crop of acorns the following year (as usually happens), seed can be collected from local sources or registered stands and directly sown as described above. Any losses after direct seeding can be easily replaced with 1 year seedlings using the the protection which is already on site.