How to Grow Globe Amaranth in Australia

Globe amaranth (Gomphrena globosa) is a warm-season annual in the amaranth family, Amaranthaceae, grown for its papery, clover-like flower heads, fresh or dried. It takes heat and dry spells in its stride and flowers from summer until the first frost. Most failures start at sowing, when seed goes into soil that is still too cold.

Three mistakes that matter

1. Sowing into cold soil. Globe amaranth is frost tender and will not grow away until the weather warms. Seed in cool soil comes up slowly, patchily or not at all. Wait for the soil temperature in When to plant, or start seed under cover.
2. Sowing dry seed thinly. Germination is often low, so a row of single seeds can leave long gaps. Soak the seed first, as set out in Sowing Seeds, sow two or three at each spot, and thin to the strongest seedling later.
3. Cutting heads too late for drying. Heads left on the plant start to lengthen and brown at the tips, and old heads can fall apart once dried. Cut them as soon as they are fully coloured and open, as set out in Harvesting and Drying Blooms.

When to plant

Sow once frost is over and the soil holds at least 20°C. Seed comes up best at 21 to 25°C, usually in 7 to 21 days. One sowing can flower from early summer until frost, so there is little need to sow in batches.

Where spring is slow to warm, start seed under cover six to eight weeks before the last frost. Plants take about 10 to 13 weeks to flower, so stop sowing once that would carry them into autumn cold.

Site, soil and setup

Give globe amaranth full sun, ideally 6 to 8 hours a day, and soil that drains freely. It copes with poor, dry soil once established, but flowers longest where compost has gone in. Slightly acid to neutral soil suits it, up to about pH 7.5.

Where leaf spot has appeared, grow globe amaranth in a fresh bed the next year. The fungus survives in old plant debris in the soil, as described in Pests and diseases.

Container growing

All four lines in the range are tall types, so allow at least 20 L of fresh potting mix per pot. Even one small plant needs a pot at least 20 cm wide and deep, and every pot needs drainage holes.

• Watering: check pots daily in hot weather and water deeply when the mix is dry 5 cm down.
• Feeding: water in fish and seaweed blend at 25 mL per 9 L every fortnight from planting until the first flowers.
• Position: the hottest, sunniest spot you have, out of strong wind.

Sowing Seeds

Start globe amaranth in cells under cover where spring is cool, or sow it direct once the soil is warm.

Preparing the seed

Soaking speeds germination. Cover the seed with warm water and leave it overnight, or for up to two days, then sow it while it is still damp. Seed treatments explains why soaking works.

Starting under cover

• Sow two or three soaked seeds per cell of seed raising mix, 3 to 5 mm deep.
• Keep the mix just moist and warm; a seedling heat mat holds it at the temperature given in When to plant.
• Expect slow growth: seedlings can take a while to make true leaves, so keep them in bright light.
• Thin each cell to the strongest seedling once true leaves show.
• Harden off seedlings over about a week (moving them outdoors for longer each day so they adjust to sun and wind).
• Plant out after the last frost, once seedlings stand 5 to 10 cm tall, 20 to 30 cm apart, and water each one in well.

Sowing direct

• Sow two or three soaked seeds at each spot, 3 to 5 mm deep, with the spots 20 to 30 cm apart.
• Keep the surface damp but never soggy until seedlings appear.
• Thin to one seedling per spot once true leaves show.
• Mulch lightly with sugar cane or pea straw once seedlings stand about 5 cm tall.

Every line sold here is labelled Gomphrena globosa, though several references list 'Strawberry Fields' under a related species, Gomphrena haageana. Despite the Amaranth on the label, none is the leafy vegetable covered in the Amaranth guide.

Care by growth stage

Warmth matters more than feeding: once nights stay mild, plants grow steadily on moderate water and little food. Weeks count from sowing.

If growth stalls in poor soil, a light dose of all-purpose controlled release granular (NPK around 14-5-10) scratched into the soil can help.

Pinching and Deadheading

Pinching is optional: it gives a bushier plant with more stems, while an unpinched plant grows taller and more open.

• Pinch once: at about 15 cm tall, snip off the top set of leaves just above a lower leaf pair with clean, sharp snips.
• Or pinch the first flowers: taking off the earliest heads has much the same effect.
• Cut often: plants bloom better when stems are cut regularly for the vase or for drying.
• Deadhead: cut faded or browning heads back to just above a set of leaves.
• End of season: pull plants once frost or cold ends flowering, disposing of spotted ones as under Pests and diseases.

Companion planting

Globe amaranth brings in bees, butterflies and other beneficial insects, and it wants the same hot, sunny, free-draining spot as other summer annuals.

Grows well with

• Zinnia: wants the same sun, heat and watering, and both suit a cutting bed.
• Alyssum: a low edging in front that leaves the stems of globe amaranth in clear view.
• Annual salvia (Salvia farinacea): a similar height and thirst, so neither crowds nor shades the other.

Keep apart

• Celosia: the same leaf spot fungus attacks both, and its spores splash from plant to plant.
• Tall crops such as corn or sunflowers on the north side: they shade globe amaranth, which flowers less well out of full sun.
• Crops watered every day, such as lettuce: soil that never dries out invites root rot.

Harvesting and Drying Blooms

For drying, cut when a head is fully coloured and fully open but still round and firm. For the vase, cut a little earlier, once the head has colour but before it is fully open.

• Cut in the cool of the morning, as stems cut in hot weather wilt quickly.
• Take the longest stem you can, cutting just above a leaf pair.
• Strip the leaves and stand vase stems in clean water straight away.
• For drying, tie small, loose bunches with a rubber band, which keeps its grip as the stems shrink.
• Hang the bunches upside down in a dry, airy place out of direct sun, usually for 2 to 3 weeks.

Dried heads hold their shape and colour well. Use them on the stem in dried arrangements, or snip them off for craft work.

Common problems

Seedlings collapse at soil level. Damping off (Pythium species and Rhizoctonia solani) rots young stems in wet, cold mix or soil, so resow in fresh mix and water less. Read more

Plants wilt with rotting stem bases. Root and stem rots take hold in heavy or waterlogged soil, so grow plants in a raised bed where water lies.

Lanky plants with few flowers. Globe amaranth tolerates part shade, but full sun gives better flowering.

Self-sown seedlings in odd colours. Seedlings that come up from dropped seed can flower in a different colour from their parents.

Pests and diseases

Globe amaranth has few pest problems. Most trouble comes from leaf disease in a run of cool, damp weather, such as a wet Melbourne autumn.

Aphids (family Aphididae). These small sap-suckers cluster on new shoots and under leaves, which can wilt or discolour and turn sticky with honeydew. Read more

Alternaria leaf spot (Alternaria gomphrenae). Tiny reddish purple spots grow into tan to grey spots with a purple rim, and bracts and stems can spot too. Splashing water spreads the spores, and infected heads can carry the fungus on their seed.

Grey mould (Botrytis cinerea). Infection starts on ageing flower heads, which rot under grey mould, mostly in cool weather with heavy dew or fog.

Prevention first

• Keep to the spacing in Sowing Seeds and pull weeds, so air moves freely between plants.
• Water the soil, not the leaves, early in the day so plants are dry by night.
• Pick off spotted leaves and old heads and put them in the bin, not the compost.
• Hose aphids off shoot tips with a firm jet, and spray insecticidal soap, mixed to the label, if they return.

Tips

1. For dried bunches, grow globe amaranth beside Statice and Everlasting Daisy, which also air-dry well for the same bunches.
2. In the subtropics, a late January sowing can still flower by March, refreshing the garden as the summer annuals fade.
3. Globe amaranth is not on the declared weed lists of Queensland, Victoria, Tasmania, South Australia, the Northern Territory or the ACT. New South Wales WeedWise has no profile for it, and Western Australia lists it as permitted.