Because many penstemons are not reliably hardy, a hard winter can result in serious losses. It is therefore advisable to propagate some fresh stock each year in late summer and keep it in frost-free conditions until the following year. Cuttings are the best method when propagating a named cultivar, as these do not come reliably true from seed. However, seed, division and layering can also be used. See the links below for more on these techniques.
This is the best method to produce plants true to the parent. Softwood cuttings can be taken any time during the growing season – those taken early in the year require bottom heat. The more vigorous cultivars, such as Penstemon 'Alice Hindley' and P. 'Schoenholzeri' can be taken early in the year (for planting out in early summer) and usually grow rapidly enough to give a flower display by late summer.
Take softwood cuttings as follows:
- Take non-flowering tip cuttings of about 10-12.5cm (4-5in) long and trim with a sharp knife to just below a leaf node
- Gently remove the bottom two leaves and trim the top and side leaves by up to one-third to reduce leaf surface area and, in turn, moisture loss
- Dip the cut ends in hormone rooting powder and insert in a 50:50 mixture of compost and perlite
- Up to five cuttings can be inserted into a 9cm (3.5in) pot, or modular trays can be used for larger quantities
- After rooting, they can be left undisturbed over winter or individually potted on
Rooted cuttings of penstemons need frost-free conditions during the winter, but can otherwise be grown with little or no warmth and should be kept as cool as practical, with good ventilation whenever possible.
Penstemons are easily propagated from seed sown in early spring in heated conditions and planted out in early summer. However they are unlikely to come true to the parent plant.
Sowing seed indoors