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I would like to try growing some oak trees from acorns. When should I collect acorns for this?

Should I pick them as soon as they appear on the tree? Or leave them a while to 'ripen', or change colour? Or wait for them to fall off the trees?

Specifically in the UK, so Sessile oak (Quercus petraea) or Pedunculate oak (Quercus robur). Or maybe more exotic oaks if I can find any.

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Collect them, as soon as they fall. There is no need to climb a tree, as tempting as it sounds.

A good acorn is fresh, rather big, feels plump and heavy, the cap comes off easily and it shows no signs of damage like holes (insects), cracks or mould.

Left alone outside, the acorn will germinate in spring or, as I have observed, some rather eager quercus robur specimens will push out their taproot during late autumn already. Most sources suggest stratification ("leaving them outside" is the easiest method), but apparently a cold and wet autumn will be enough already.

  • If you want to sow them in directly the garden, burying them ca. 1 inch deep in a well-mulched bed is your best option in my experience: I have pulled dozens and dozens of "volunteers" over the years... If you want to transplant them, note that oaks have a strong taproot, so dig deeply and carefully. I suggest transplanting the seedlings in early spring, right after germination. Plant enough, in case squirrels, jays or other animals step by for their share - or consider netting.
  • In pots, the same rules apply: plant as soon as possible, leave the pots outside and enjoy your seedlings come spring. Don't forget to water during winter if necessary. Note that narrow, but high pots are better suited for oaks than shallow and wide ones, the kind used for roses is excellent.

There is no need to fuss with the seeds themselves, like breaking or cutting the outer shell. Another question about red oak discusses the questionable necessity in detail and I simply wouldn't bother.


Side note, speaking from experience with quercus robur:
They come in two varieties, one will drop all leaves in a very short time in autumn, the other will hold onto most of them until spring, when the new leaves literally "push off" the old brown ones. Apparently this is a hereditary trait with regional prevalence of either kind. If you like, you can observe your potential "parents" and pick whichever you prefer.

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There are various methods for growing from acorns, many involving soaking them and peeling the skin off, or putting them in a refrigerator for a while (not necessary in the UK) but the simplest is probably the one outlined in the link below, aimed at children, where you just stick 'em in a pot.

You can wait for them to fall from the tree, then pick them up as soon as possible, but they should not be old, damaged or dried out - the cap should come away easily from the bottom, and only use acorns which are undamaged. If you try picking them from the tree, you may find the cap doesn't part from the acorn.

https://www.rhs.org.uk/education-learning/gardening-children-schools/family-activities/grow-it/grow/oak

When you stand the pot outside, if you have lots of squirrels around, it's probably wise to cage or protect the pot in some way to keep them from digging up the contents - the highest risk of this happening is from mid September up to mid November.

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