Gardens: Go forth and propagate

Growing new plants from cuttings is a canny way of building up your stock of tender annuals

 

If I sawed my finger off and stuck it in a pot of soil, it would be a little unreasonable to expect it to grow a whole new “me”. And yet that’s pretty much what happens when you grow a plant from a cutting. Do it right and within as little as a few weeks, you’ll have a

baby plant, genetically identical to its parent but entirely capable of independent life. Amazing.

It’s not just its cost-effectiveness that makes propagating plants from cuttings such a worthwhile skill to cultivate. It also allows us to grow varieties no longer commercially available, or plants of special personal significance. That might be an heirloom rose flourishing in a friend’s garden, or a rosemary bush grown from a sprig that was once part of a bridal bouquet.

Cuttings are also an excellent way of swiftly building up stock of some tender annuals. Tomato plants, for example, can be easily grown from cuttings taken in mid-spring. And then there are other plants, such as dahlias, which are more vigorous and floriferous when grown from cuttings taken in spring rather than from overwintered tubers.

When is the best time to take them? Depending on the particular plant, cuttings can be taken as softwood in late spring/early summer, semi-hardwood/ semi-ripe in summer/early autumn or hardwood in late autumn/winter. Those technical-sounding terms might sound off-putting, but are simply a reference to the plant propagation material used. Spring growth is typically soft and sappy, hence the term softwood, but becomes twiggier, or ‘harder, as the year progresses.

Softwood cuttings are bursting with growth hormones, and root the most quickly, sometimes startlingly so. Many climbers, trees, shrubs and perennial plants including clematis, pelargonium, Michaelmas daisies, dianthus and penstemon, can easily be propagated in this way.

I’m now the smug owner of several dozen shrubby salvias grown from softwood cuttings taken in May, from plants overwintered in a friend’s polytunnel. Taken as short stem-tip cuttings, just below a leaf node and in early morning, these were gently stripped of their lower leaves and very quickly ‘planted’ into a two-litre pot filled with good-quality seed-and-cuttings compost (roughly five cuttings per pot), before being watered, covered with a Ziploc plastic bag, sealed with an elastic band and then placed on a heated propagator out of direct sunshine. Most were ready to pot on and harden-off within the month.

Spurred on by my success, this summer I took semi-hardwood cuttings of Hydrangea ‘Annabelle’, a hardy, vigorous variety with large snow-white flower globes that appear in mid-summer, before slowly fading to lime-green. Step-by-step, the process was much the same as for the salvia cuttings, except that as semi-ripe cuttings, these were soft at their tip, but firm at their base and slightly longer (10-15cm) than their softwood equivalents (7.5cm).

This time, the propagation material came from a large plant bought in a garden centre for exactly for that purpose. Again, they rooted quickly. By late September, I had a dozen baby plants.

Others plants eminently suited to being propagated from semi-hardwood cuttings include many shrubby evergreens such as rosemary, sage, lavender, box, escallonia, holly, viburnum, hebe, camellia, ceanothus, cistus and choisya.

Meanwhile, the sight of this month’s colourful leaf-fall signals the beginning of the hardwood cuttings season. Technically, this continues until leaf buds burst into growth next spring, but success rates are highest when cuttings are taken between late October and early December.

Plants best suited to being propagated by hardwood cuttings are deciduous and include roses, philadelphus, buddleia, elder, cornus, forsythia, jasmine, Vitis, honeysuckle, willow and many varieties of fruit, including currants, gooseberry and mulberry. Ideally, the cuttings should be from this year’s growth, taken just below a leaf node, 15-30cm long and no more than the thickness of a pencil, with the top slanted so you know which way is up, and with two-thirds of the stem buried below the surface.

Take care to choose a healthy parent plant free from pests or disease and use a sharp, sterilised secateurs. If you’re growing in pots, give the latter a good scrub before use. Careful labelling is key and should include the date the cuttings were taken, along with the name of the parent plant and the garden it came from.

As plants are dormant and temperatures and light levels are low, hardwood cuttings inevitably take longer to establish. While it’s possible to grow them outside, placing potted cuttings in a heated, covered propagator or a polytunnel/glasshouse/cold frame will speed up the process and increase the strike-rate, as will the use of hormone-rooting powder. As with any type of cutting, you’re still unlikely to have 100 per cent success, so take more than you need.

A brief few words on PBR, or ‘Plant Breeder’s Rights’, a legal term to which I’m philosophically opposed, but of which gardeners need to be aware. Any plant with these initials after its name is deemed to be a form of intellectual property in the same way that a painting or a piece of music is. To propagate it without permission is technically illegal. As to how you’d be found out, that’s a bit of a puzzle …

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