Maintaining Your Herbs
Herbs are generally quite robust plants but appreciate a little attention. Leaving them to do their own thing is tempting, but many can get carried away if untended and spread themselves everywhere, so maintaining them is essential.
From: DK Books - Herbs
Spread Out the Workload
Throughout the gardening year there is always something that can be usefully done, but in spring and fall there rarely seem to be enough hours in the day, so get as much done in the winter as you can. Try to plan your new schemes in the fall so the hard digging can be done on dryer days in early winter and the soil can be ready for planting in the spring. Pruning and cutting back do not have to be done in the fall—left standing, stems and seedheads provide a habitat and food source for wildlife. In summer, much of the harvesting, pruning, and pinching out is best done in small doses—it makes the process more enjoyable.
By pinching out the growing tips of herbs such as basil (Ocimum), the plant bushes out as its energy is redirected to lateral buds lower down the stem. Avoid the temptation to just pick off the odd leaf.
This is essential to reduce competition for light, water, and nutrients, but take care not to damage your herbs by over-enthusiastic hoeing. This can be an easy task if done regularly, but onerous if left too long.
Do this as the seeds ripen if you want to harvest them or prevent wanton self-seeding. Remember, though, that some can look good in winter and are also a useful food source for the birds.
Horseradish is a large, vigorous plant whose tasty roots can taper down over 60 centimeters into the soil and can be very difficult to dig out. It will spread quite rapidly and if you really do want to grow this plant, it would be a good idea to give it its own raised bed within which it can be contained. It will need to be fed extra compost or manure as it requires a fertile soil to produce a good crop and really won’t be productive in a pot.
Removal of the herb, if it has taken over, is arduous and it is important to remove every fragment of root from the soil, as each piece is capable of regenerating and growing to full size within a season or two.
Melissa officinalis and alliums
Lemon balm can set seed prodigiously and in time it springs up in every crack or crevice. The flowers are small and insignificant, which can make it difficult to know when to deadhead. An easier method is to cut the whole plant down to within 6 inches of ground level as soon as it is 20–24 inches tall. Alternatively, plant its cousin Melissa officinalis "Aurea," which is more compact and seems to be a bit better behaved.
Alliums can also become a problem as they copiously set seed as well. The seedlings appear in spring but are easy to gather and use as baby chives. Alternatively, hoe them off before they become established.
Mints (Mentha spp.)
These are renowned for rapidly spreading and invading ground where they are not wanted, quickly forming a mass of intertwining stems, roots, and suckers. Avoid this by planting in a container, but do make sure that the drainage holes are blocked with landscape or weed-control fabric as mint will find and exploit any avenues to escape. Bury or sink containers in the ground to just below the rim, but keep a watchful eye as laterally spreading suckers or runners will soon extend beyond the edge and will root very rapidly. Despite this, mints are an essential herb, but do try to avoid planting several types of mint per container as one will become dominant and overpower the rest.