Getting it to bloom

Why won't my Penstemon 'Sour Grapes' bloom? (and how to make it flower)

Also called Sour Grapes beardtongue (Penstemon 'Sour Grapes').

More about penstemon 'sour grapes'

About Penstemon 'Sour Grapes'

Penstemon 'Sour Grapes' · also called Sour Grapes beardtongue · flowering

Penstemon 'Sour Grapes' is admired for its unusual smoky blue-violet tubular flowers, flushed grey-purple with pale throats, carried on upright spikes from early summer into autumn. A bushy semi-evergreen perennial with narrow leaves, it is a bee favourite and flowers for months when deadheaded. Like most border penstemons it wants full sun and fertile, sharply drained soil to survive winter.

Plant type: flowering

Watch for — Reduced flowering without deadheading: Spent spikes slow new bloom. Deadhead regularly and grow in full sun to extend flowering well into autumn.

The reasons penstemon 'sour grapes' isn't blooming

Almost every non-blooming penstemon 'sour grapes' traces back to one of these, roughly in order of how common they are:

Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.
Too much nitrogen feed, driving lush foliage at the expense of flowers (very common with general or lawn feeds).
The plant has not been deadheaded, so it stops flowering once it sets seed.
Irregular watering — drought or waterlogging at the budding stage makes buds abort.
It is still too young or was checked by a transplant and is rebuilding before flowering.

Feeding penstemon 'sour grapes' a high-nitrogen general feed and growing it in too little sun — you get a big leafy plant and almost no flowers.

The fix — how to get penstemon 'sour grapes' to flower

Maximise sun. Give penstemon 'sour grapes' the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers.
Switch the feed. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.
Deadhead regularly. Remove spent flowers often to keep it producing more rather than stopping to set seed.
Water consistently. Keep moisture even through budding and flowering — drought-then-flood swings make buds drop.

Light and feeding do most of the heavy lifting here. Dial in the spot with the light guide for penstemon 'sour grapes' and get the feeding right with the penstemon 'sour grapes' fertilising schedule — the wrong feed (too much nitrogen) is one of the most common silent reasons a healthy plant makes leaves instead of flowers.

Bloom season and what to expect

Penstemon 'Sour Grapes' flowers across its growing season (mostly summer) and, kept fed and deadheaded, can bloom for many weeks or right up to frost.

Post-bloom care so it flowers again

Deadhead, keep feeding lightly, and many will rebloom; collect seed from the best plants at the end of the season if you want to grow them again.

For everything else this plant needs day to day, see the full penstemon 'sour grapes' care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Penstemon 'Sour Grapes' blooming — frequently asked questions

Why won't my penstemon 'sour grapes' flower?

Penstemon 'Sour Grapes' blooms on the season's growth given enough sun, warmth and the right feed — there is no cold or photoperiod trick, just good growing conditions and a bloom-leaning feed. The most common reason it is not happening: Too little sun — most of these need full sun (or very bright light) to flower well; shade gives leaves, not blooms.

How do I make penstemon 'sour grapes' bloom?

Give penstemon 'sour grapes' the sunniest spot you have — for most bedding and fruiting plants, more direct light directly means more flowers. Move off high-nitrogen feeds and use a higher-potassium "bloom" or tomato-type feed as it comes into flower.

When does penstemon 'sour grapes' normally bloom?