Penstemons are easily grown from seed, which may be sown in the open in late fall, or at any time during the winter. Seed beds should be very firm, almost hard; seed of the large seeded kinds should be planted about 1/4 inch deep. Those of the tiny seeded species should not be covered over 1/16-inch, or they may even be sown on the surface and pressed into the soil.
For those who do not have room for seed beds, the seed may be sown in flats that are carried out of doors over winter. The flats may be filled with soil, with a 1-1-1 mixture of peat moss, vermiculite and perlite is preferred. This sterile medium almost eliminates the danger of damping off, and seedlings can be removed from it with minimum root damage. Of course, it is necessary to feed the seedlings with a nutrient solution about every ten days.
Plants in this mixture can be grown to transplanting size, if the seed is not sown too thickly. Several hundred plants grown in this medium were transplanted directly to the field, during the last week of June with a loss of less than a dozen plants. By late August many of the transplants were in bloom and continued until hard frosts in late October.
Plants from the nursery, or from your seed bed can be transplanted with minimum care. The root system is much like that of a strawberry, and transplanting is done in the same manner. It is helpful to build a little cone of soil in the bottom of the planting hole, and to spread the fibrous roots over that. The crown of the plant should be at soil level with the roots well spread. The soil should be well packed over the roots and watered. The crown must not be covered with soil. Soil should be kept moist during establishment, but should not be kept muddy.
Penstemons can be transplanted at any stage of growth as dormant plants, rapidly growing plants, or even while in full bloom.
Rules for Growing Success
There are only a few rules for success with penstemons in the garden, but those are important.
First: Penstemons must have good drainage. They cannot abide wet feet. The surest way to lose them is to keep the soil waterlogged. In the wild and in the garden, the best specimens are those grown in gravelly soil, or on steep banks where drainage is rapid. Overwatering often results in overgrown plants that sprawl all over the garden. Many species are native to arid climates and require little water after establishment. This drought tolerance makes them ideal for steep slopes, dry walls or the wild garden.
Second: Don’t fertilize heavily. Penstemons are light feeders. Overfertilization will cause rank, weak growth, or may even kill the plants.
Third: Give them room… they don’t like to be crowded. They love light, so plant them in the sun. No rule can be formulated for use in the garden, beyond suggesting that the tall ones be used in the background, the short ones in the foreground and the intermediates in between.
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