How to Grow Penstemons

Dampen a paper towel and sprinkle seeds on it. Roll the paper towel up loosely with the seeds inside, and put it in a plastic bag. Place it in the crisper drawer of your refrigerator.

Check the paper towel two or three times each week to make sure it hasn't dried out. If it feels dry, lightly moisten the paper towel and return it to the refrigerator. After 40 to 45 days, you should see some tiny green shoots. All viable seeds will germinate within several days of each other, and are ready to be planted in soil as soon as shoots appear.

Mix four parts seedling soil with one part sand and fill a 4-inch pot with the medium. Place a germinating penstemon seed on the surface. Dampen the soil slightly, but don't wet it. Penstemons do not like too much water.

Turn a plastic bowl upside down and cover the pot to create a humid environment for the developing seed. Check every day for the appearance of true leaves. When leaves appear, mix a little fertilizer in water according to the packaging instructions so that it is only ¼ strength. Use an all-purpose fertilizer with high phosphorus and low nitrogen content. Give the seedling a light watering with the diluted fertilizer mix. Set the pot where it will receive as much light as possible until the seedling grows to 1 inch tall.

Take the potted seedling outside every morning once it's 1 inch tall. Set it in full sun as soon as temperatures reach about 50 degrees F at midday. It will develop sturdier roots and stem if allowed to be tossed around by the wind, heated up by sunshine and cooled with rapid temperature fluctuations. Bring the seedling back inside before dusk.

Plant the penstemon seedling in full sun in well-draining soil in early May. Space plants about 18 inches apart. Leave the top of the rootball just above the surface of the soil. Don't bury the plant's crown. Mulch with gravel or leave them unmulched. Don't use compost, grass clippings or bark for mulch, all of which promote disease in cold, wet weather. Keep the garden well weeded while the penstemons are young plants.

Water penstemon plants only when they're dry, and let them dry out in between waterings. Their roots don't go deep into the soil, so you only have to water to a depth of 3 to 4 inches.

Apply a light feeding of fertilizer in the fall. These tough plants only require an annual application.

Let some of your penstemons set seeds by not de-heading them. The resulting seedling volunteers will live longer and be more durable than the parent plant.