Most
penstemons are not reliably hardy in many parts of the UK
and a hard winter can result in serious losses. It is therefore
advisable to propagate some fresh stock each year. This can
be done from seed or by division or layering. Cuttings are
best used when propagating a named cultivar, as these do not
come reliably true from seed.
Tip cuttings can be taken any time during the growing season, those taken early in the year requiring bottom heat. The more vigorous cultivars, such as Penstemon 'Alice Hindley' AGM and P. 'Schoenholzeri' AGM can be taken early in the year (for planting out in the following season) and may grow rapidly enough to give a flower display in late summer but it is always a good idea to take cuttings late in the season, in case some of the garden plants do not overwinter successfully.
Non-flowering
tip cuttings of about 10-12.5cm (4-5in) long should be taken
and trimmed 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.
Dip
the cut ends in hormone rooting gel or powder (decant a little
first to avoid potentially contaminating the entire pot) and
insert in a 50/50 mixture of compost and vermiculite.
Up to five cuttings can be inserted into a 9cm (3.5in) pot, or modular trays can be used but for larger quantities. Another approach is to insert the cuttings in a prepared rooting bed in a sunny, wall-side cold frame, spacing 7.5cm (3in) or so apart. 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.
It is best not to cut down the old flower spikes until the following spring as this material will protect the plant from frost during the winter. In spring when new shoots appear at the base then the old flower spikes can be removed and suitable material used as cuttings.