Used oak barrels from distilleries and wineries make sturdy planters that can hold larger shrubs, small trees or groupings of flowers. You can make two large planters from each barrel by cutting it in half. Leave the outside the natural oak colour or paint it in a colour to contrast with the blooms it will contain. If the barrel has been stored in a dry area for a while, tap the bands toward the centre with a hammer or let it sit in the rain to let the wood swell, so the wood staves will be tight before you cut the barrel apart.
Measure halfway between the two ends with a tape measure and draw a pencil mark. Measure again every few inches and connect the pencil marks to draw a line around the centre of the barrel.
Cut the barrel in half using a circular saw, sabre saw or hand saw. If the metal bands seem loose, turn the half-barrel bottom end upward and tap the bands down with a hammer until they fit snugly. Nail three or four tacks just above each band, spaced equally around the barrel, to keep the bands from slipping down when you turn the half barrel right side up again.
Drill four drain holes in the bottom of each half with a 1/2-inch drill bit.
Turn the half-barrels upright again and fill the bottom of each one 2 to 6 inches deep with packing peanuts, to minimise the weight and help with drainage. Fill the rest with potting soil or topsoil to within 3 to 4 inches of the top.
Make a hole in the soil that's the size of the root ball (if you're transplanting a shrub, flower or other plant that's already started). Use a trowel to dig a large hole or push the soil aside with your hand for a small plant. Remove the plant from its previous container, set it in the hole, gently spread its roots and carefully press the dirt around it, filling any air pockets without breaking the roots. If you're planting seeds, plant them the recommended depth and press the soil gently over them. Water the soil and keep it slightly damp for the first few days, until the seeds germinate or the plant begins to grow new roots.