Choose the Clay and Plan the Height Before You Touch a Coil

A tall planter has to survive British winters, so the clay body matters more than the profile. Use a grogged stoneware or a crank body with 20–30% fine grog. The grog opens the clay, reduces shrinkage and gives the fired wall a little elasticity so it can cope with repeated freezing and thawing. Low-fire terracotta can be beautiful, but a tall, thin-walled terracotta planter outdoors will often spall or crack once water sits in the pores.

Decide the finished size before you begin. A planter 45–60 cm tall and 30–35 cm across at the rim is a comfortable target for herbs, and it holds its own on a patio. Bear in mind roughly 7–10% shrinkage from wet to fired, so measure and draw a simple outline on paper, marking the widest point and the rim diameter.

Aim for walls 8–10 mm thick. Thinner than that and a tall pot will flex and slump under its own weight; much thicker and the wall holds so much water that frost damage becomes likely. Work in sessions of an hour or two and let the pot firm up between them rather than trying to finish it in one sitting.

Make the Base and Start the First Coils

Roll or throw a base slab about 10 mm thick and cut a clean circle. Add a drainage hole — 12–15 mm is plenty for a planter of this size — plus two or three smaller holes if you like. Score the top surface generously, paint on thick slip and let it sit for a few minutes until tacky.

Roll your first coil to roughly 2 cm thick, working along the whole length with a flat hand so the diameter stays even. Press the coil onto the scored rim of the base, working right around without stretching it. Join the ends with a diagonal cut so the seam overlaps rather than butts together.

Blend that first coil into the base thoroughly with your thumb, then run a wooden rib along both the inside and outside to weld the join and compress the clay. This bottom joint carries the most weight, so give it more attention than you think it needs.

Join Every Coil Properly — Score, Slip and Compress

The strength of a coil pot comes almost entirely from how well each coil is joined to the one below. Work in short sections, maybe 15 cm at a time, rather than rushing around the whole circumference.

• Score the top of the previous coil with a fork or a serrated rib.
• Add slip — a thin cream of the same clay body — and let it go tacky.
• Press the new coil down and slightly outward with your thumbs.
• Blend the join with thumb and forefinger, inside and out.
• Compress the wall with a wooden rib, downwards and outwards, closing any trapped air pockets.

Trapped air is the enemy. Any void left inside the wall will expand in the kiln and can blow a hole in the pot, and it creates a weak point for frost. If you feel a soft, spongy patch, dig it out with a pin tool and fill it with fresh clay.

Support the Walls as the Pot Rises

Once you pass about 20 cm, gravity starts to win. From here on, every session should end with the pot supported and covered.

Wrap the outside of the pot with a couple of layers of newspaper taped in place, or with bubble wrap held gently with an elastic band — never tight enough to mark the clay. A soft support like this stops the belly from bulging overnight. Alternatively, fill the pot loosely with a bag of dry sand, which supports the wall from within while it firms up. A wooden bat or a stiff card disc laid across the rim helps keep it circular.

Work on the pot in stages. Build 8–10 cm, shape and smooth it, cover the whole thing with a plastic bag and leave it overnight. The clay stiffens enough to carry the next coil without slumping. Turn the pot a quarter turn each session so you are not always working from the same side, and keep a mirror or your phone camera behind the pot to check the silhouette honestly.

Shape the Profile and Finish the Rim

With a firm wall, shaping becomes possible. Paddle the outside gently with a flat wooden bat while your other hand supports the inside, or push outwards from within with a rib to find a gentle swell. Work in small increments and check the profile against your drawn outline. Keep the base slightly narrower than the shoulder so the pot looks deliberate rather than heavy.

For the rim, add one final coil and press it so the rim reads a fraction thicker than the wall — this resists chipping when pots are moved. Round it over with a damp sponge and check it is level all the way round by turning the pot slowly on its bat. Add three small feet or a bevelled base ring if you want the pot lifted clear of wet paving, which helps drainage and reduces frost damage.

Dry Slowly and Fire for Outdoor Life

Dry the finished planter under a plastic bag for two to three weeks, opening the bag a little more each week. Rushing this stage is the most common cause of cracking. Turn it every few days so no one area stays damp and cool.

Bisque fire to around 1000°C, then glaze fire to 1220–1260°C for a fully vitrified stoneware. Leave the foot and the lower outer wall unglazed, or use a satin glaze with a good grip — glossy, slick surfaces on the base can trap water against the clay in frost. A well-made, well-finished planter of this kind will hold thyme, rosemary and mint happily for years, and improve with the weather.