Terence Baker describes the methods he uses to propagate plants for the National Collection.
The Foxglove (Digitalis purpurea), so much a part of the British countryside, is perhaps one of the few native plants to be well received in gardens. They do seem to have the ability to spring up almost unnoticed, that is until their towering flower stems dominate the garden. Once there, few gardeners have the heart to remove them, thus insuring more in future seasons, for Foxgloves are great seeders.
Digitalis purpurea is just one species of a genus containing, depending on which books you read, more than twenty species, geographic variations, hybrids and abnormalities. Some are known and are commercially available garden plants, others are obscure and sought after. Several, as yet, appear to be known only in Botanic Gardens and in the collections of enthusiasts. All are interesting and worthwhile plants. In the main they are hardy but some are resentful of our winter wet, or are naturally so floriferous as to be short lived.
Some species, such as D. grandiflora, x mertonensis, parviflora, are sound perennials especially if divided, which can be tricky! Other such as D. ferruginea are biennial and like so many biennials are best considered monocarpic, that is they die after setting seed, therefore with the exception of sterile hybrids they are best propagated by seed. Seed is available of at least half the species in general cultivation from various seed companies. Many of the rest can be obtained from seed lists of various societies as well as the National Collections, enthusiasts and botanic gardens. The seed is fine, uniformly sized and easy to handle. When possible it is best collected as soon as the capsule splits. When ripe the best and most viable seed will fall easily into a paper envelope, any that remain may not be of such good quality and attempting to dislodge it may well cause the good seed to be polluted with capsule debris, a potential hazard.
Once collected there is much to be said for sowing some as soon as possible, the seed is generally ready by early August and sowing at this time allows the young plants to become established before any hard weather. Such sowings may be over-wintered in a well ventilated cold frame or, in the case of less hardy species, a frost free glasshouse, for planting out in early April.
Depending on the quantity required, 4 inch (10cm) half pots or seed trays may be used. A seed tray will easily accommodate several hundred seedlings, far more than the average gardener requires even to support local NCCPG or other sales. Do not sow too thickly. Ideally the young plants should not touch. A good quality seed compost should be used, this should be levelled and gently firmed in the usual way. Once sown do not cover the seed as Digitalis require light for germination, this accounts for the failure described by some gardeners. The seed should be lightly pressed into the compost. I prefer to water-in overhead with a very fine rose watering can. Watering overhead is preferred as a general rule because this can reduce any germination inhibitors that adhere to the seed of some genera. If you would prefer not to use a can, then the sown pots may be stood in a shallow depth of water, once the surface of the compost darkens the container should be removed, the compost should not be allowed to become sodden.
The containers should be covered with clean glass. If the seed is sown in late summer a shaded cold frame or cool greenhouse is a suitable environment, or the north side of a wall; high temperatures should be avoided. If the seed is to be spring sown it should be stored in a dry paper bag or envelope which must be kept cool and dry under which conditions the seed lasts well. Long term deep refrigerated storage in a sealed container with silica gel is possible, this should last indefinitely.
Spring sown seed usually in March is sown in the same way, preferably in a frost-free glasshouse. Earlier sowing in January will produce plants which may well flower the first year from seed. Such sowing should be made in a warm glasshouse or propagator kept at 60-65°F (15-18°C). Whichever way is chosen the resulting plants should be pricked out. In the case of species the strongest should be chosen. With hybrids try retaining some of the weakest plants as these occasionally produce the most interesting colours. Both should be potted into small pots.
Alternatively seed can be sown directly into the flowering position and if kept moist germination takes about 21 days and, when large enough, the resulting seedlings may be thinned to stand about 12 inches (30cm) apart. Generally the species will come true from seed, however hybrids and forms will intercross; parent plants should be isolated to avoid confusion.
Terence Baker is the holder of the National Collection of Digitalis. He runs the Botanical Nursery in Wiltshire.
Source of article
Growing From Seed - Winter 188-89 Vol. 3 Number 1
© The Seed Raising Journal from Thompson & Morgan
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