With a bumper crop of acorns this year, if you haven’t already planted some, now is the perfect time to give nature a helping hand to create the next generation of oak trees. In this article, we’ll try and cover the most common question on acorn harvesting and planting for maximum success.
Acorns are best harvested directly from the tree, as soon as they are easily detachable from their cups. From a practical point of view, this means that trees with low hanging branches are much easier to harvest from. You can collect acorns that are lying on the ground, but these are much more likely to be damaged in some way, including by pests.
It’s also ideal to harvest acorns from old trees rather than young ones: old trees have seen it all and survived weather of all sorts, and have built up immunity to pests and diseases. Given that there are quite wide variations in climate, finding your donor tree immediately adjacent to where you want to plant is the best option, but not always possible.
If you can't plant your acorns immediately, then they can be stored for a few weeks as long as they are kept moist and cool – a sealed Tupperware container or similar stored in the fridge works well. If they dry out they will not germinate.
When you are ready to plant, test the acorns to ensure they are hard with a quick squeeze – any soft ones should be discarded. If you have a lot to test, you can also put them in a bucket of water and discard any that float.
Acorns should ideally be planted on their sides, since both the tap root and the shoot grow from the point of the acorn. If you can plant them in their eventual location this will save moving the sapling later and will give the tree the best chance to get established well in the critical early years. Plant the acorns approximately 2” deep because squirrels LOVE acorns, and will try to dig them up either to eat or to hide in a winter larder. If you do lose acorns to squirrels it may work out in the end – they don’t take them far and you may find young oak saplings appearing in strange places which you can reclaim later! [We accidentally left a bag of approximately 200 harvested acorns out overnight, and found the next day that all of them had vanished. A few shells showed that there had been some limited snacking the previous evening, but the bulk of the acorns had just vanished, buried somewhere no doubt].
If you can’t plant directly into the ground, you can plant into pots for transplanting as one-year-old saplings. Choose deep pots because the tap root on oak grows long quite quickly, and again plant the acorns on their side about 2 inches from the top. If you are using compost (though topsoil is fine) please try and use peat free compost, which is just as good (if not better) than the peat variety without the detrimental environmental impact of peat. Once planted up, if you can place the pots in a fruit-cage, this will prevent the squirrels from ‘borrowing’ your acorns.
If you’re planting at scale, then pots aren’t a practical solution and planting in rows directly in the soil is the best option. Here we’ve planted acorns about 2” deep and 6” apart since this is not their eventual site. Transplanting oak saplings is surprisingly easy, ideally done over the winter after the first frost.
One of the most fascinating differences between ancient woodland and new plantings, is the difference in biodiversity. A square metre of ancient woodland can have as many as 60,000 different types of beetles, bugs and fungi, and this biodiversity is key to carbon capture. Transplanting a handful of topsoil from nearby ancient oaks jump starts nature’s process, injecting mycorrhizal fungi into the soil around your acorns, which will help your young oak to get established successfully.