Getting it to bloom

Why won't my Flat Sea Holly bloom? (and how to make it flower)

Also called Flat Sea Holly, Blue Eryngo, Blue Sea Holly (Eryngium planum).

More about flat sea holly

About Flat Sea Holly

Eryngium planum · also called Flat Sea Holly, Blue Eryngo · flowering

Eryngium planum is a vigorous, long-lived perennial native to central and eastern Europe and central Asia, producing masses of small, oval, steel-blue flowerheads on branched stems from midsummer to early autumn. It is one of the hardiest and most floriferous sea hollies, widely used in meadow plantings, cottage gardens, and as a cut flower. Full sun and sharply drained soil are the key requirements — the blue colouring intensifies with more sun and poorer soil. The genus Eryngium is considered non-toxic to cats and dogs.

Plant type: flowering

Watch for — Leaf and bud eelworm: Microscopic nematodes cause angular brown patches between leaf veins and distorted, stunted buds; destroy affected material and do not replant Eryngium in the same spot.

The reasons flat sea holly isn't blooming

Almost every non-blooming flat sea holly 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 flat sea holly 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 flat sea holly to flower

Maximise sun. Give flat sea holly 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 flat sea holly and get the feeding right with the flat sea holly 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

Flat Sea Holly 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 flat sea holly care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Flat Sea Holly blooming — frequently asked questions

Why won't my flat sea holly flower?

Flat Sea Holly 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 flat sea holly bloom?

Give flat sea holly 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 flat sea holly normally bloom?