Propagating your own herbs is a rewarding occupation and the
best way to replace plants and to stock your garden economically. The basic techniques are not difficult, but, as herbs are such a disparate range of plants,
their requirements and the degree
of difficulty in raising them varies. Some are much easier to propagate than others. Many respond better to one method than another so check for
the optimum propagation method for each plant.
Raising from Seed
Many herbs are easy to grow from seed. Spring is generally the best time for sowing, but do not start too early: seeds sown when air and soil temperatures are warmer and light levels higher will grow into stronger plants. Some seeds are sown in autumn, as indicated here.
Annuals: All annuals – plants whose life cycle is completed in one year – can be grown from seed sown in spring. Hardy annuals, such as chervil (Anthriscus cerefolium), coriander (cilantro) (Coriandrum sativum) and pot marigold (Calendula officinalis) may also be sown in autumn to give them an early start the following spring. Half-hardy annuals, such as nasturtiums (Tropaeolum spp.), should not be sown until late spring or early summer in areas where there is frost. Basil (Ocimum basilicum) is tender and should be sown in seed trays under glass in late spring to early summer.
Biennials: These are planted in the late summer or early autumn of one year, to flower the following year – though some of them go into a third year, their life cycle is over once they have flowered. Although parsley is a biennial, it is worth sowing seed every year because the stems coarsen and it does not produce such good leaf in its second year. Biennials include angelica (Angelica archangelica), caraway (Carum carvi), clary sage (Salvia sclarea) and evening primrose (Oenothera biennis).
Perennials: These live for a number of years and many perennial herbs can be successfully raised from seed. But not all of them produce seed, such as French tarragon (Artemisia dracunculus) and the non-flowering golden sage (Salvia officinalis ‘Icterina’). Many hybrids and cultivars do not come “true” from seed, which means they may vary considerably from the parent plant. This includes all the mints, most lavenders and orna-mental thymes. These must be vegetatively propagated.
Vernalization: A few herb seeds need to be subjected to a period of intense cold before they will germinate. In the wild, this ensures their survival where winters are cold. To reproduce these conditions artificially, in a process known as “vernalization” or “stratification”, put the seeds in a polythene (plastic) bag of moist sand and leave in a refrigerator or freezer for 4–6 weeks before sowing.
This is necessary for: aconitum or monkshood (Aconitum napellus), arnica (Arnica montana), agrimony (Agrimonia eupatoria), juniper (Juni-perus communis), hawthorn (Crat-aegus laevigata), Primula spp., Rosa spp., sweet cicely (Myrrhis odorata), sweet woodruff (Galium odoratum) and sweet violet (Viola odorata).
Scarification: Some hard-coated seeds, such as those of legumes, which include broom, clovers and vetches, will germi-nate more readily if first rubbed with fine sandpaper. This breaks up the outer coating and allows moisture to pene-trate, which all seeds require before they will germinate.
Sowing in seed trays
The success rate for seeds sown in trays under controlled conditions is higher than for seeds sown outdoors. It is the best method for very fine seeds, such as parsley, and essential for raising tender plants, such as basil. It is also a good way to give many plants an earlier start.
Many seeds can be sown outdoors directly into the soil where they are to grow, or in nursery beds for later transplantation. It is also the sensible way to raise herbs that do not respond well to being transplanted. These include coriander (cilantro), chervil and dill. It is as well to remember that there
is a higher failure rate for seeds sown outdoors, rather than in a tray in the greenhouse, due to unexpected adverse weather conditions or the unwanted attention of birds or rodents. On the other hand it saves time and energy in pricking out, potting up and hardening off, and plants raised this way are often sturdier. For a good chance of success with outdoor seeds:
• It is best not to start too early in spring, if still cold. But to speed things up cover the area with cloches for a week or two in advance of sowing to warm up the soil.
• First weed the area thoroughly and rake it to a fine texture and level surface.
• Next make a shallow depression with a stake, or rake handle, in the soil and sprinkle in seeds as thinly as possible. Larger seeds, like nasturtiums or coriander (cilantro) can be placed indi-vidually rather than scattered.
• Cover seeds with a thin layer of soil, patting it down lightly, but beware of burying them too deeply.
• Don’t forget to mark the area planted clearly. Sowing in straight lines, as appropriate for producing some culinary herbs, makes it easier to distinguish seedlings from weeds.
• Water well after planting and keep the area moist until the seedlings appear.
You Will Need
Cellular seed tray; soilless seed and cuttings compost (soil mix); watering can; herb seeds; garden sieve; label; polythene (plastic) dome or plastic bag; 7.5 cm
(3 in) pots
Sowing in seed trays
1. Fill a seed tray with soilless growing medium. A tray divided into cells makes it easier to sow thinly and to pot up seedlings with minimum root disturbance. Water first, then scatter two or three seeds in each compartment.
2. Cover the tray with a layer of sieved compost (soil mix). Never bury seeds too deeply, especially small ones such as parsley. Water again and don’t forget to label the tray (tiny seedlings look similar).
3. Put a polythene (plastic) dome over the tray, or enclose it in a plastic bag, to retain moisture. Put the tray on a windowsill or in the greenhouse until the seedlings emerge.
4. When the seedlings come through remove the cover and put the tray in a light place out of direct sunlight. Keep moist, but never waterlogged.
5. As soon as the seedlings are large enough to handle, pot them up in 7.5 cm (3 in) pots filled with fresh potting compost (soil mix). When strong and bushy they can be planted out.
Many herbs, such as rosemary and southernwood, are best propagated from cuttings. It is also the only way to perpetuate a special flower colour, such as pink-flowered hyssop, or a leaf variation, such as variegated rue. Stem cuttings are all taken in the same way. Do not cram in too many cuttings or put one in the middle of the pot.
You Will Need
Plants; sharp knife or secateurs (pruners); polythene bag; hormone rooting powder; 15 cm (6 in) pot; cuttings compost (growing medium); dibber (dibble), pencil or stick; plastic dome or bag
1. Collect only a small amount of material at a time and be sure to keep in the shade in a polythene bag, to minimize water loss. Choose sturdy, non-flowering stems, with lots of leaves. Cut a section about 10 cm (4 in) just below a leaf joint and remove all but the top two or three leaves. These are necessary to supply the plant with nutrients as the root system develops.
2. Dip the cuttings into hormone rooting powder, tapping off any excess, and insert them into holes made with a dibber (dibble) round the edge of a pot filled with moist cuttings compost (growing medium). Water lightly and cover with a plastic dome or polythene
bag held over a wire frame and sealed at the bottom –
this is to maintain maximum humidity.
3. Once the cuttings have rooted – 2–4 weeks for softwood cuttings, 4–6 weeks for semi-ripe cuttings – repot into new compost and harden them off gradually before planting out.
A method of increasing herbs with creeping roots, such as mint (Mentha spp.), soap-wort (Saponaria officinalis), bergamot (Monarda didy-ma) and herbs with taproots such as horseradish (Armor-acia rusticana).
You Will Need
Garden fork; mint, or other suitable plant; secateurs (pruners); seed tray; cuttings or all-purpose compost (growing medium); watering can
1. Lift a root of mint and cut
it into 4 cm (11⁄2 in) pieces. Try to cut at a point where there is a small bud from which a new plant can grow.
2. Fill a seed tray with cuttings compost. Lay the pieces of root on the surface, press them in and cover with a further layer of compost. Water and leave in a shady place. There is no need to cover the tray or enclose it in polythene, but do keep it moist.
3. Once there are plenty of leaves showing through, divide the new plants and grow them on in bigger pots or plant them out in the open ground.
Division of roots
Herbs with fibrous or fleshy taproots are very easy to propagate by division. These include: chives (Allium schoenoprasum),oregano (Origanum spp.), lemon balm (Melissa officinalis), lovage (Levisticum officinale) and comfrey (Symphytum spp).
Division of roots
1. Dig up a clump of chives. Divide it into several new pieces, pulling it apart with your hands or the aid of a small fork if necessary.
2. Cut off some of the top growth. Replant in open ground or firm each new piece into a pot filled with all-purpose compost.
3. Keep the new plants well watered. They will soon grow strongly to provide plenty of fresh leaf.
A useful method of propagation for shrubby herbs such as bay, rosemary and sage. It works by inducing a side stem to develop new roots while still attached to the parent plant. Mound layering is particularly suitable for thymes, which become straggly after a few years. Pile gritty loam in a mound over the lower, leafless stems, leaving the crown of the plant showing. This stimulates new roots to develop at the base, when they can be separated and then planted in a different position.
1. Trim the lower leaves from a side stem, attached to the shrub. Bend it over and bed into soil beside the plant.
2. Fasten it down with a staple or peg. Water in and leave for several months until roots have formed. Divide the new plant from the parent and replant it.