Herbs: propagating

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When to propagate herbs

The best time to bulk up herbs depends on the growing habit and life cycle of the individual herbs.

• Sow seeds of annual and biennial herbs such basil, coriander, dill and parsley in spring and throughout the growing season at three week intervals until August
• Take cuttings of shrubby herbs such as hyssop, rosemary, sage, thyme in late spring
• Divide hardy herbs such as sweet marjoram, Oregano, Mint (Mentha) and thyme in spring or after flowering in late summer
• Take root cuttings of mint in spring

How to propagate herbs

Here is a guide to propagating some of the commonly-grown herbs.

Basil (Ocimum basilicum)

• Sow seeds of basil indoors on a sunny window sill or in a propagator in a greenhouse
• After May, you can sow basil direct into garden soil. As soon as the seeds have germinated, sow more to keep supplies constant. However, one sowing is usually sufficient for a summer's supplies

Bay (Laurus nobilis) AGM

• The easiest method is to take semi-ripe cuttings in late summer or early autumn
• Dividing suckers in spring is also possible, as is simple layering

Caraway (Carum carvi)

• Sow seeds in early autumn or spring in modules or pots or directly into the soil in drills. Thin seedlings to 20cm (8in)

Chervil (Anthriscus cerefolium)

• Sow seeds outside in early to late spring, once the soil has reached a temperature of 10°C (50°F)

Chives (Allium schoenoprasum)

• Sow 10-15 seeds per 3cm (1¼in) module in spring in a propagator with bottom heat of 18°C (64°F)
• Divide bulb clumps in spring or autumn

Coriander (Coriandum sativum)

• Coriander can be sown in late spring directly into garden. As soon as the seeds have germinated, sow more to keep supplies constant. Sometimes coriander self sows and will appear the following year

Dill (Anethum graveolens)

• Sow seeds outdoors, shallowly in poor soil in early spring or outdoors in late spring. Thin seedlings to 20cm (8in) apart. Repeat sowing every three weeks ensures constant supplies

Marjoram (Origanum vulgare)

• Take softwood cuttings in summer
• Divide in spring
• Sow seeds thinly on the surface of the compost  in spring

Mint (Mentha spp.)

• Take softwood cuttings in summer
• Rhizome cuttings can be taken in spring. Plant the runners 5cm (2in) deep and 15-22.5cm (6-9in) apart
• Divide in spring

Parsley (Petroselinum crispum)

• Sow seeds in early spring with a bottom heat of 18°C (64°F) or in late spring 0.5cm (¼in) deep in rich soil. Use fresh seed. Germination is slow. A second and third sowing in late spring and late summer ensure supplies for summer and autumn

Rosemary (Rosmarinus officinalis)

• Take semi-ripe cuttings in late summer or heel cuttings in spring
• Rosemary can be layered or mound-layered in summer

Sage (Salvia officinalis)

• Take heel cuttings or 15cm (6in) softwood cuttings in early summer
• Simple layering after flowering is successful as is mound layering in spring
• Sow seeds in spring and cover them with perlite. It is useful to provide a bottom heat of 15°C (59°F)

French tarragon (Artemisia dracunculus)

• Tarragon can sometimes, with great difficulty, be propagated by taking softwood cuttings in summer
• Underground runners are produced from which root cuttings can be taken in spring after frosts
• Divide mature plants every two to three years in spring

Thyme (Thymus vulgaris)

• Take softwood cuttings 5-7.5cm (2-3in) long in late spring or summer
• New plants can be produced by simple layering in early autumn or mound layering in spring
• Sow seeds indoors in mid-spring
• As thyme quickly becomes woody, plants are best replaced every two or three years

How to mound layer herbs

This is a useful method of propagation for plants that have become woody. Lavender, sage and thyme are particularly prone to being short-lived and can be rejuvenated following this method;

1. In spring, make a mix of equal parts peat-free compost and sand
2. Mound the mixture over the plant so that you can still see the tips of the shoots and keep it watered
3. Replace any soil that may be washed away by rain
4. Roots should have formed along the stems by late summer. These rooted layers can be detached and potted up or planted out as for simple layers
5. The old plant can then be disposed of

Problems

Herbs are usually trouble-free plants, but there are a few pests and diseases that may cause problems;

Damping off can occur in growing environments that are badly ventilated or humid. Mint rust can affect marjoram and savory as well as mint species.

Rosemary beetle can be a problem on lavender, sage and thyme as well as rosemary. Sage leafhopper is also responsible for causing fine, yellow flecking on the foliage of many aromatic plants including sage, mints, lavender, bergamot, marjoram, oregano, rosemary, basil, thyme and lemon balm. Only treatments suitable for edible plants (as described on the label) should be used.