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How to plant, grow & care for penstemons

How to plant, grow & care for penstemons

It’s no secret that I’m a huge fan of colour in the garden and on that front alone, penstemons more than deliver. Available in a whole boudoir-full of silky, satiny hues, these easy-to-grow, drought-tolerant perennials flower for months on end, attracting clouds of pollinators, especially bees to their beautiful, bell-like blooms. I love to grow them in our borders – they look great beneath roses – but they’re perfect for pots, and for the cutting garden too, offering up flowers from July to the first frosts. I hope you enjoy our wide range of penstemon plants, available as single varieties or as ready-made collections that we know will look fabulous.

DetailsWhere & when to plantHow to plantCare guidePests, diseases & common issuesFrequently asked questions
Details
Calendar
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Jun J
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Sowing
Planting
Flowering
Seasonal checklist
Spring
  • Sow seed under cover in early spring.
  • Plant out. Wait until after the last frost for young or tender plants.
  • Cut back old growth on established plants as new shoots start to appear.
  • Mulch border penstemons and apply a general-purpose fertiliser to potted plants.
Summer
  • Cut back flower spikes after blooming.
  • Take cuttings to make new plants for next year.
  • Regularly feed and water plants in very dry soils or in pots.
  • Deadhead old flowers, and pick stems to enjoy indoors.
Autumn
  • Mulch around plants with dry matter to protect over winter. 
  • Keeping picking stems for the house.
Winter
  • Leave old stems standing over winter to protect the plant from frost. If they are in a windy spot, reduce stems by a third.
  • Wrap potted penstemons with hessian or bubble wrap.
  • Plan which penstemons you’d like to grow next year.

Where & when to plant

Where to plant

Soil type

Penstemons are happiest in fertile, relatively moist but well-drained soil. 

Aspect & position

Full sun and a sheltered spot out of cold winds will suit penstemons well.

When to plant

March to mid-May is the best time to plant container-grown penstemons, though you can plant them any time from March until October. Just remember to water if the soil is dry. 

How to plant

We’ve done a bit more of the legwork here for you, so if conditions are right, you can plant these straight into your containers or the garden by following the instructions below. If weather conditions aren’t right (i.e., they are too cold or too wet) then you can pot them on into a 1 or 2 litre pot before planting.

Step 1.

Prepare the planting area by forking over the soil and incorporating plenty of organic matter (well-rotted manure, home-made compost or multi-purpose peat-free compost). Pick out any large stones and visible weeds as you go.  If you are on heavy clay then incorporate some horticultural grit to improve drainage.

Step 2.

Water your plants well before planting. You can also soak them for 20 minutes in a bucket or wheelbarrow of water if they seem particularly dry.

Step 3.

Rake to level the soil, breaking up any large clumps. Try to create a fine, crumbly soil texture. The young plants roots will like this. 

Step 4.

Dig planting holes deep and wide enough to cover the roots. Adding rootgrow into the bottom of the planting hole will help plants establish roots 

Step 5.

Position the plant in the hole, leaving the crown of the plant (where the roots meet the top growth) just level with the soil surface. Fill the space around the plant with the displaced soil, and gently firm the soil with your hands. You should be able to tug gently on the leaves without the planting lifting out of the ground. 

Step 6.

Water well, and once it looks like all the water has been absorbed, water again with a really good amount of water (not a sprinkle). Do this every 5-7 days (if there has been no rain) to encourage roots to be drawn down deep into the ground, resulting in stronger plants. For more top tips on watering visit our guidehere.

Step 7.

Remember that plants tend to look better in groups of three, five or seven, and allow about 45cm between plants in borders. 
Photography by 
Jonathan Buckley
Care guide

Watering

Water penstemons well until established. Mature plants in good soil should not need watering, but plants in sandy soils or potted plants will do. Give the plants a good drink every couple of weeks, so that the soil is just moist. 

Fertilising

Feed plants in pots once every one or two weeks to prolong flower production. 

Deadheading

Deadhead by removing spent flower spikes. You can also give your plants the ‘Chelsea chop’ in late May by cutting stems back by up to a half. This will delay flowering by up to a month – useful if you want to stagger the blooms in your garden.

Propagating

FROM CUTTINGS

Some penstemons are tender, so it’s a good idea to take some cuttings as a form of insurance.

The easiest way to propagate penstemons is by taking semi-ripe cuttings from mid-summer to mid-autumn, following the steps below:

  • Choose leafy, flower-free shoots about 15-20 cm long from this year’s growth, where the base of the shoot is just beginning to harden. Cut cleanly and place in a plastic bag to prevent them drying out.
  • Trim to just below a leaf node and remove the soft tips, leaving a cutting of 10-15cm.
  • Remove the lower leaves so that just about four remain.
  • Fill a container with peat-free potting compost mixed with 50 percent sand or grit and push in the cuttings deeply around the edge of the pot, taking care that they don’t touch each other. 
  • Water and move to a cool place out of direct sunlight, undercover.
  • Monitor to ensure the soil stays moist (but not wet).
  • Pot up plants when you see roots emerging through the base of the pot, remembering to keep them protected from frost over winter.

FROM SEED

Penstemon grown from seed may not match the parent plant exactly, but will introduce more diversity into your garden. For best results, sow penstemon seed undercover from February to April. Seeds may need cold stratification.

  • Fill divided seed trays or Jiffy modules with peat-free compost and moisten well. Sow thinly on the surface of the compost (they need light to germinate) and place in a propagator or on a warm windowsill (a temperature of 15-20°C is ideal), and cover with a clear plastic bag to keep the soil moist. 
  • Keep the surface moist but not wet. Once plants have germinated, remove the bag. If more than one seed per module has germinated, remove the weaker seedling. Water sparingly.
  • When you can see roots filling the bottom of the module, pot the seedlings on into 9cm pots, pinching out the growing tips when the plant is about 8cm tall to encourage bushier growth.
  • Plant out after the frosts, hardening the plants off over 1-2 weeks before you do so. 

Cutting back

Leave old stems on penstemons over winter to protect the plant from frost. If the plant is in a windy spot, you can reduce stems by a third to avoid windrock. Cut the stems back hard in late spring, just as new shoots begin to develop.

Overwintering

Hardy penstemons in the ground should be fine (just leave the old stems standing). It’s a good idea to protect potted plants with some hessian or bubble wrap.

Pests, diseases & common issues

Penstemon are generally trouble-free but frost can cause damage, so keep the plants in a sheltered spot and mulch the crowns, or wrap potted plants over the winter. 

Powdery mildew

Powdery mildew – a fungal disease causing dry, dusty patches – can be an issue in dry periods. To try to avoid it, plant plants in full sun and not too densely – you want the air to circulate – and water regularly in dry spells. Choose varieties with good mildew resistance. 

At Perch Hill we use a homemade spray as a preventative. To make it, mix 1 tsp bicarbonate of soda, 1 tsp vegetable oil and 1 tsp soap (we use Uncle Tom’s natural soap) with 400ml water and pour into a spray bottle. Shake well and spray on leaves, including the undersides.

Rust

Spots on penstemon leaves can be a sign of rust and other fungal diseases. We don’t recommend fungicides, so advise that you rake up and dispose of fallen leaves around the plant and mulch well. To avoid fungal diseases, plant plants with adequate spacing so that air can circulate. It’s also a good idea to avoid overhead watering, and to water in the morning so that moisture does not sit on the leaves.

What is eating my penstemon?

Penstemon are generally not attractive to slugs, deer or rabbits, but if these are a problem in your area, it’s worth trialling just one or two plants before planting more.

Why are my penstemon not flowering?

There are a few reasons why your plant might not be flowering, including too much shade, poor drainage or a nutrient deficiency. Follow the steps above to ensure your penstemon is grown in the correct way. It’s worth noting too that penstemons are fairly short-lived plants, lasting about three to five years. Flowering will decline as the plant ages. 

Why is my penstemon falling over?

Penstemon are prone to being damaged in strong winter winds, so cut old stems back by a third in autumn to protect against this.

Why are my penstemon leaves turning brown?

Penstemon can suffer from eelworm which causes leaves to dry and drop, and which can cause the plant to die. 

If your plant has eelworm, dig it up and dispose of it. Either dig out and replace surrounding soil, or avoid planting penstemons in the same spot for a few years.

Why is my penstemon wilting?

Wilting penstemons might have too much water, causing root rot, or too little. Stick your finger into the soil – ideally it should be moist, but not soggy, at about an inch deep. 

Photography by 
Jonathan Buckley

Frequently Asked Questions

  • Are penstemons hardy?

    Some penstemons are hardy and some are more tender. As a general rule of thumb, those with thinner leaves tend to be hardiest.

  • Do penstemon spread?

    Penstemons will spread slowly to form small clumps. They are not considered invasive, though they can self sow.

  • Are penstemons drought tolerant?

    Yes penstemons are drought tolerant and, if in good soil, will thrive in dry periods. 

  • Can you grow penstemon in pots?

    Yes, penstemons grow well in pots.

  • do penstemons need full sun?

    Yes, full sun is ideal for penstemons, although they can also handle light shade.

  • Do penstemons die back in winter?

    Yes, penstemons are herbaceous perennials, so they die back in winter and regrow in spring.

  • Are penstemons poisonous to dogs or cats?

    No, penstemons are not considered toxic to dogs or cats.

  • Are penstemons evergreen?

    Penstemons are semi-evergreen, meaning they retain some of their foliage over winter.

  • Are penstemons the same as foxgloves?

    No, penstemons are not the same as foxgloves though they are in the same family (scrophulariaceae) and have flowers which look similar.

  • Wht to grow with penstemons

    Penstemons look great with grasses and other herbaceous perennials including lynchnis, echinacea and aconitum. At Perch Hill, we grow them under roses, where they take over after the polyanthus have finished blooming in spring.

How to cut and arrange penstemons

Since they produce so many flowers, it’d be silly not to cut a few for the house and that’s just what we do, adding them to arrangements from late summer until the frosts. Cut in the morning and sear the stems by submerging them in an inch or two of boiling water for 30 seconds, then pop straight into the vase, where they will last for up to a week.

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