Although many edible plants are grown in pots, most fare best in open ground. By and large, though, herbs break this rule and thrive in containers, and now is the time to refresh or replace them.
It is an advantage to have obligingly mobile plants like these. You can put the pots in a prominent place when the herbs are at their best and make them less visible while dormant. Use them to brighten walls, steps and tables, placing them in full sun in summer and protecting them over winter. The positives of pots are endless: move them out of the way for a party or shift them around the patio to suit your latest design plans.
Mediterranean sun lovers, such as thyme and rosemary, are perfect for containers: they require the poor, gritty soil that's easy to provide, and thrive in small pots that limit the supply of nutrients. Thymes need two-litre pots; winter savoury and hyssop do well in five litres; while the larger lavender and oregano thrive in 15-litre containers. During the summer, the sides of pots warm up and keep the compost that bit drier, which is vital to success.
At the other extreme to thymes, a few herbs – mint being one – spread like wildfire and need to be kept under control: a pot makes the perfect prison. Another candidate for this control is ramsons, or wild garlic. I'm delighted to see it carpeting a bank by my burn and supplying lots of delicious garlicky flowers and leaves to adorn a salad, but it would be a different matter in a garden.
By using a pot, you can even prevent the umbellifer, sweet cicely, from spreading. Given half a chance, it forms a large clump and I've found its huge tap roots can do terrible damage to the crazy paving in my herb garden. But, like ramsons, its leaves are well worth having: they add delightful fragrance to stewed fruit. Sweet cicely only lives a couple of years in a 15-litre pot and the wonderfully flavoured lovage, which reaches three metres in the open ground, may not last more than a year. Treat these as annuals.
If you've been overwintering some herbs, such as hyssop or winter savoury, check if they should be repotted. Cut away any dead stalks and straggly bits and take the herbs out of their pots. If you're confronted with a massive root ball, transfer the plant to a larger pot. If possible, use homemade compost, mixing in grit for much-needed drainage, and scatter grit round the root collar to prevent rot. Trim the roots and repot, with the soil level 2-3cm below the rim to prevent water running over the sides.
If you don't need a larger pot, fork in extra compost – wormcast is unquestionably the best, but ordinary homemade or even commercial compost will be fine. You'll want a good harvest of fresh leaves, so give your plants a little extra feed.
Without the space to overwinter the likes of rosemary, French tarragon or bay, you'll find this is a good time to buy a replacement. In fact, it's often easiest to treat a lot of herbs as annuals; get them growing well and enjoy fresh pickings throughout the summer. When you bring herbs back from a garden centre, you'll almost certainly have to transfer them to a larger pot. Nurseries keep plants healthy in tiny pots by watering frequently and using slow-release fertilisers, but most of us won't be able to do this.
Some of the herbs treated as annuals need much more water than the Mediterranean ones, and include parsley, chives, garlic chives and salad burnet. These plants, together with equally thirsty sorrel and perennial rocket, require 10-litre pots. It'll make life easier if they're grouped near a source of water and they'll also create an envelope of humid air around themselves.
You will need to provide some protection for annuals such as dill. It struggles in the herb garden but when grown in my polytunnel it grows up to a metre and a half and lasts all summer. It will do well in a 10-litre pot but is shorter lived, so if you want a steady supply you'll need to sow every few weeks throughout summer. Treat chervil and annual rocket the same way.
Some herbs – coriander, lemon grass, hot chillies and basil – need even greater warmth than dill. All these plants need the heat and sunlight a greenhouse or conservatory offers. But don't despair if you haven't got a greenhouse – just make a bit of space on a sunny window sill.
While you're making all these plans for fragrant dishes for summer and autumn, go a step further and think ahead for Christmas. Buy a rosemary plant, grow it on and trim to the shape of a Christmas tree – the perfect festive table decoration.
