How to Grow Penstemon Seeds

Grow Guide #2383
Family: Plantaginaceae
Binomial name: Penstemon sp.
Life Cycle: Perennial

This 'How to Grow' guide details everything a home gardener needs to know to plant, grow and care for Penstemon (Penstemon sp.).

When to Sow Penstemon Seeds

Penstemon is a perennial plant that grows year round in most climates. Use the table below to identify the best time of year to sow penstemon seeds in your climate.

Preparation

Penstemon plants are short-lived perennials, meaning they usually live for between two and five years. Choose a permanent position where plants can grow undisturbed by regular digging or disturbance.

Penstemon plants are best grown in full sun or part shade. Choose a location that will receive at least 3 hours of full sun each day.

Penstemon plants need a well drained soil enriched with plenty of organic matter. Prepare soil by weeding it thoroughly, digging it over to loosen it and adding aged animal manure or compost. Keep the area free of weeds until planting. Learn more about preparing soil for planting here.

How to Sow Penstemon Seeds

Optional: Stratifying seeds prior to planting may improve the speed and success of germination. Stratification involves exposing the seeds to a period of cold temperature which for some species helps to break dormancy and spur the seeds to germinate. Read more about stratification here.

Penstemon seeds can be sown directly into the garden OR seedlings can be raised in trays or other containers and transplanted to the garden once established.

Sow Direct

1. Sow seeds directly in the garden 2mm deep and 40cm apart.
2. Keep soil moist but never wet or dry.
3. Seeds should germinate in around 14-21 days at a soil temperature of 20-24°C.
4. Young seedlings will need protection from pests, pets and weather until they are established.

Raise Seedlings

1. Fill trays, punnets or jiffy pots with a good quality seed-raising mix, or use soil starter pellets.
2. Sow seeds 2mm deep.
3. Keep soil moist but never wet or dry.
4. Seeds should germinate in around 14-21 days at a soil temperature of 20-24°C.
5. Transplant seedlings to the garden once they have their first true leaves and are large enough to handle (usually 5-10cm tall).
6. Plant out, spacing plants 40cm apart.

Tip: Seeds of this variety can be slow to germinate. Take note of the expected germination time, be patient and follow the recommended depth and temperature guidelines closely for the best chance of success.

How to Grow Penstemon

Penstemon plants may need watering during the growing season. Water when the soil is dry about 5cm below the surface (test this by scratching away a little soil with your finger). Water deeply in the early morning or late afternoon. Avoid watering the leaves of plants to avoid fungal diseases. Learn more about watering here.

If soil was well prepared no extra fertiliser should be necessary. In poor soil or to give your plants an extra boost, application of a high-potassium fertiliser or one formulated for flowering plants can be beneficial:

• Apply slow release fertiliser at the recommended rate when transplanting or when seedlings are 5-10cm tall.
• Apply liquid fertiliser at the recommended rate and frequency while plants are fruiting or flowering.

Penstemon plants should flower in approximately 85-100 days.

Deadhead penstemon flowers regularly during the growing season. Using sharp secateurs or snips cut fading or dead flowers off just above a set of leaves. Removing old flowers regularly will encourage plants to produce more flowers. Learn more about deadheading flowering plants here.

When plants have finished flowering prune them back to neaten them and encourage strong new growth. Using sharp secateurs or snips, cut individual stems just above a set of lower leaves.

Common Problems when Growing Penstemon

Like all plants, penstemon is susceptible to some pests, diseases and other problems. Below is a list of the most common problems gardeners encounter when growing penstemon plants:

• 

  Aphids are small (2-4mm long) sap-sucking insects that congregate on the new shoots or the undersides of leaves. They can cause leaves to wilt or become discoloured, and also excrete honeydew which can attract ants and other insect pests. To manage aphids, remove them by spraying with a garden hose, apply a soap or alcohol spray, or encourage predatory insects to your garden. Read more about aphids here.
• 

  Bacterial leaf spot is a disease that causes irregularly shaped brown spots on all above-ground parts of a plant. The spots at first appear to be wet but become dry and scab-like over time. Leaves and flowers can fall prematurely. Water plants at soil level (not on the leaves), dispose of fallen leaves and fruit and practice crop rotation.
• 

  Rust (Puccinia sp.) is a fungal disease that causes brown to orange raised spots or patches to appear on foliage. Fungal spores are spread by wind or water to neighbouring plants, especially in temperatures of 10-20C and when humidity is high. To manage rust, space plants to avoid overcrowding, grow them in the recommended amount of light (eg full sun), do not over fertilise crops, remove dead plants and practice crop rotation. Read more about rust fungus here.
• 

  Powdery mildew is caused by fungal spores reproducing on the leaves of plants. First showing as white spots on leaves, affected areas can spread quickly to cover the entire leaf surface. While rarely fatal, powdery mildew can reduce yields. Water plants at soil level (not on leaves) to prevent spreading spores, allow good air flow between plants, remove affected leaves and if necessary spray with an appropriate fungicide or homemade spray. Read more here about powdery mildew here.
• 

  Slugs and snails are molluscs that feed on tender leaves and shoots, mostly at night, leaving slimy trails behind them. Control them by removing their hiding places, keeping free range poultry, collecting them by torchlight or by placing traps. Read more about slugs and snails here.