Division
Propagating plants from division is, literally, dividing your existing plant into sections, each section then growing into a new plant.
Division is usually done in spring when the plant starts its growth cycle or autumn/winter when the plant is dormant. It is mainly done on plants which naturally self-divide (eg Saxifraga paniculata) and herbaceous perennials with fibrous roots (eg Aster frikartii ‘Mönch’), although it is also a useful method for some herbaceous plants with more fleshy roots and a few woody shrubs and trees.
Most herbaceous perennials will actually benefit from regular division, every three to five years.
Herbaceous perennials (including grasses)
Division is usually done in spring, but check the plant information for the plant in question, as some can be divided in autumn or winter. To divide a plant, first use a garden fork to gently lift it from the soil (or remove it from its pot if it’s container grown), causing as little damage as possible to the rootball. This is easiest done by working your fork under the roots then levering it out of the ground. Shake the soil from the roots or wash it off using a hose or by dunking the rootball in a bucket of water.
Study the plant to identify any obvious lines of division and any dead/dying material which you wish to discard. Where possible the plant should be gently pulled apart into clumps by hand, which does less damage to the roots. Make sure that each piece has a good root system and several strong shoots at the top.
If the plant cannot be divided by hand then you can use a small handfork to tease the roots apart, two garden forks back to back to lever the clump into sections, a spade to chop through the centre or even a knife (an old bread knife is ideal) – but whichever method you use you should cause the least possible damage to the plant. Divide the plant in half to begin with, then each half into smaller sections.
If any roots have been damaged by the division process then use a pair of secateurs to trim them back to the very top. This will remove any damaged sections which would be vulnerable to disease and will encourage new root growth.
Don’t be tempted to divide the plant into too many small pieces, each one must be strong enough to grow on its own.
Re-plant each divided piece into well prepared soil which has had bulky organic matter dug in (eg garden compost or farmyard manure) and some slow release fertiliser added. If possible, re-plant the divisions in a different area, this will help prevent the build up of pests and diseases common to that plant in the same spot. You can plant smaller pieces in pots or a nursery bed so that you can monitor them more carefully as they grow on. Ensure that pots are not exposed to cold weather (eg if you did your division in autumn) as this may damage the roots (which have been used to being nice and cosy in the ground).
Divided sections should be re-planted as soon as possible. If you are unable to re-plant them immediately then heel them into the soil or cover them with moist sacking or similar to prevent them drying out.
Make sure that each divsion is well watered until it is established. It would help to add a mulch to retain water and minimise weeds.
Single bud division can also be used on some herbaceous perennials, although the smaller pieces resulting from this will need more aftercare to successfully grow on. Hostas, for example, are good candidates for this form of division. Lift the plant then pull the crown apart into single, strong buds, each with a good section of root attached. Grow them on in a sheltered nursery bed or pots, planting them to the same depth they were originally. Ensure that they do not experience extremes of temperature until well established.
Bulbs and corms
Bulbs and corms naturally increase in number by forming clumps of bulbs or cormels/cormlets, drawing energy from the parent bulb or corm. These can take several different forms:
- Offsets – bulbs or corms which are attached to the parent bulb or corm.
- Bulblets – tiny bulbs formed around the parent plant, such as on the stem of lilies below ground.
- Bulbils – tiny bulbs formed in the leaf axils or flowerheads of the parent plant, such as lilies (leaf axils) and alliums (flowerheads).
A few tubers (eg dahlias) also form clumps of offsets which can be divided, but most tubers don’t and must be propagated by seed.
To remove offsets, dig up the parent plant taking care not to damage the delicate offsets. Remove the offsets by hand or, if this isn’t possible, cut them off with a clean, sharp knife, applying funigicide to the cut areas afterwards. Off sets which are near the size of the parent bulb or corm can be planted out and should flower the following year. Smaller ones can be grown on for a couple of years in a nursery bed or in pots. If using pots, make sure you put offsets of roughly the same size in each pot so you can transplant them all at the same time when they are big enough. The pots should be filled with half compost and half grit to ensure good drainage and kept in a sheltered location where they will be protected from the extremes of hot and cold. Offsets grown on in nursery beds should be shaded to protect them from harsh sunlight and a cloche or fleece for frosty nights. Feed and water the offsets regularly while they are in active growth to bulk them out, keep them just moist in their dormant season.
To propagate from bulblets, lift the parent plant carefully and gently pull the bulblets from around the stem. For bulbils, either snap them off the plant or wait for them to be shed naturally and pick them off the ground. In both cases they should be planted and cared for in the same way as offsets.
Rhizomes
Some perennials (eg irises) produce swollen, horizontal lumps above their roots, called rhizomes, which can also be divided in a similar fashion. Lift the whole plant with a garden fork and shake the roots and rhizome free of soil. Using a clean, sharp, straight knife cut the rhizomes into sections, each one having a strong root system and a fan of leaves attached. You can throw away any old sections which have little or no roots or top growth.
Dust all cut surfaces with a fungicide powder to prevent rotting and trim the leaves to about 15cm (with a point at the top) to prevent them being blown about in the wind, then re-plant the divided sections so the surface of each rhizome is just exposed above the soil so they get plenty of sun.
Firm in well and ensure each division is well watered until it is established.
Acquatic plants
Many acquatic plants can be divided in the same way as described above. However, some produce small ‘plantlets’ which can be separated from the parent plant (some by simply pulling off, others by severing with a knife) and grown on individually.
Roses
Species roses, such as Rosa rugosa, which are usually grown on their own rootstock (rather than being grafted), will produce suckers from their base. These can be removed in the late autumn or early spring. Remove the soil around the sucker and cut it from the rootstock, retaining as many roots as possible with the sucker. Re-fill the soil around the parent plant and plant the sucker in a deep hole to the same level it was originally in the soil. Firm well and water.
