Getting it to bloom

Why won't my Hogweed bloom? (and how to make it flower)

Also called Hogweed, Common Hogweed, Cow Parsnip, Keck (Heracleum sphondylium).

More about hogweed

About Hogweed

Heracleum sphondylium · also called Hogweed, Common Hogweed · flowering

Heracleum sphondylium is a robust native biennial or short-lived perennial of European hedgerows, roadsides, and rough grassland, thriving in moist, fertile soils in sun or partial shade. It forms dramatic flat-topped white umbels up to 15 cm across and can reach 2 m in height. The single most important care fact is that its sap contains furanocoumarins that cause phytophotodermatitis — severe blistering when sap-covered skin is exposed to sunlight — so always wear gloves when handling. The plant is considered mildly toxic to cats and dogs due to its phototoxic furanocoumarin content.

Plant type: flowering

The reasons hogweed isn't blooming

Almost every non-blooming hogweed 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 hogweed 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 hogweed to flower

Maximise sun. Give hogweed 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 hogweed and get the feeding right with the hogweed 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

Hogweed 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 hogweed care brief and its watering schedule — a stressed, badly watered plant rarely has the energy to flower at all.

Hogweed blooming — frequently asked questions

Why won't my hogweed flower?

Hogweed 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 hogweed bloom?

Give hogweed 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 hogweed normally bloom?