Your Guide To Managing Purple Top Weed


Purple top weed is known for being extremely drought hardy which in turn, makes it a major agricultural hurdle for Aussie farmers to overcome. 

Originally native to South America, purple top weed is also known as blue heliotrope. An 1879 description of the plant published in The Australasian newspaper casts it as “the bane of good land in Queensland and New South Wales, born in America, evidently badly brought up, and not kept within bounds in its young days”. While able to withstand less than favourable conditions, the real danger with purple top weed is the threat that it poses to livestock – so what do you need to know?

Getting To Know Purple Top Weed

Purple top weed actually belongs to the Boraginaceae family of plants, which also include forget-me-nots, comfrey, yellow burrweed and even Paterson’s Curse. As a noxious weed to  pastures, crops and fallows, roadsides, footpaths, lawns, parks, gardens, disturbed sites, waste areas, open woodlands and grasslands in the warmer temperate, sub-tropical and semi-arid regions of Australia – the good news is that it does have a distinct “look”, making it relatively easy to recognise.

Shape – A summer-growing, prostrate perennial herb, purple top weed (or blue heliotrope) can grow up to 15-30 cm high and 30-200 cm in diameter. This weed can get so big it’s important to nip it in the bud as soon as you spot one. 

Stems – It has many hairy, branched stems radiating from a woody rootstock, and is highly aromatic. Purple top weed has a strong, slender taproot that can be very woody. It generally extends to over one metre in height, but has been observed at up to two metres throughout the soil profile, with a complex system of lateral roots occurring at several depths.

Leaves – The leaves are alternate, dull green, soft and tapered at both ends.

Flowers – The flowers are bluish-purple with yellow centres. They grow in dense clusters along one side of a coiled stalk, often referred to as a fiddle neck.

The danger with an infestation of purple top weed to crops and pasture is the danger that it poses to livestock. This weed contains high levels of pyrrolizidine alkaloids, which can cause liver damage, brain damage and even death if consumed by cattle, horses, sheep and pigs. Thankfully, animals won’t generally consume it until left with no other alternatives, but it’s still important to eliminate the risks wherever possible.

How Purple Top Weed Spreads

Purple top weed has unfortunately adapted to a wide range of habitats, and can reproduce from both seed and root fragments. It spreads aggressively, as it produces many sticky seeds that attach themselves to both animals and machinery, with seeds also able to be passed unharmed through the digestive tracts of most animals. Unsurprisingly, purple top weed can also regenerate from root fragments. It is most commonly spread by road graders, farm machinery, livestock, humans and the movement of water along watercourses.

Flowering is largely dependent on rainfall, but usually starts in November and continues through summer until March in Australia. In frost-free areas, the plant is capable of growing and flowering at any time of the year after rain. Established plants produce a flush of new growth in spring and autumn, flowering profusely at these times. In warmer areas, plants may flower and set seed as early as July. The fruit develops into two nutlets, each containing two seeds.

The plant is frost-susceptible, dying off in winter and regenerating from the vigorous root system in the following spring.

Controlling Purple Top Weed

While hand plucking weeds is usually classed as the easiest, cost-free and efficient method used to prevent a weed infestation – it’s certainly not the most convenient, especially in large scale operations like crops or pastures. 

In comparison, a glyphosate-free weed killer like Bioweed is a safe way to keep invasive purple top weeds under control. As a non-residual solution, it will break down into the soil in as little as 72 hours and can combat over 200 invasive weed species. The best part? It can be used to defend your garden, lawn, crops and even pastures against a large variety of foreign invaders, without the need to relocate any pets, kids or livestock. 

With a team of highly experienced plant and gardening enthusiasts, the team at Bioweed are armed with a wealth of knowledge, tips and tricks that can help you to get your lawn and garden looking their very best. Please don’t hesitate to get in touch with us if you’re looking for further organic weed management solutions.