How to Grow Capers in Australia

The caper bush (Capparis spinosa) is grown for its flower buds, the capers of the kitchen, and its green fruit, the caper berries. It is a sprawling, long-lived shrub of the caper family (Capparaceae). Once settled it asks for little: full sun, hot summers, stony ground and almost no water. The hard part comes first, because caper bush seed is slow and patchy to sprout, and most failures happen before a single leaf shows.

Three mistakes that matter

1. Sowing untreated seed and giving up early. This is the commonest failure: water alone rarely wakes caper seed, and what does sprout can take months. Soak, chill and soak again as Germinating the seed describes, then wait three months.
2. Planting in wet, rich or shaded ground. Capers want the top 20 to 30 cm of soil dry and free-draining, and humid, soggy sites can kill them. Plant on a raised mound in full sun, as Site, soil and setup sets out.
3. Disturbing the roots at transplanting. Caper seedlings are notoriously touchy about being moved, and some wilt and die. Give each one its own pot early, and plant it out with the whole root ball intact.

When to plant

Caper seed sprouts in warmth, about 21 to 29°C. Sow treated seed in spring once nights stay mild, and plant seedlings out after the last frost. Start the soak and fridge chill about ten weeks before your sowing month. A bush lives for decades, so a single sowing is usually enough.

Seedlings sown late in the window go into winter small. Keep them in pots under cover until the following spring, then plant them out.

Site, soil and setup

Wild capers grow on old walls and in rock crevices around the Mediterranean, and a garden site should copy that: heat, sun and sharp drainage.

Build a low mound of free-draining, gritty soil over the bed so rain runs away from the crown. Dig in a 5 cm layer of compost, and test the pH (see soil pH explained). Below 6.3, dig in garden lime at 100 to 200 g per square metre 4 weeks ahead. Give the bush a permanent spot outside the vegetable rotation.

Container growing

A pot keeps roots dry in a wet district and lets a young plant come under cover in winter. The catch is a smaller harvest, because the bush wants a big root system. Use a pot at least 40 cm wide, about 28 L, and preferably 50 cm wide, about 52 L. Fill it with potting mix blended with a quarter perlite and a quarter coarse sand. The store sells one form, sold as Caper Bush, so there is no compact variety to choose. Seed-raised plants vary, some upright, some sprawling and some far richer in buds, so keep the best if you raise several.

• Water: only when the top 2 cm of mix is dry, and never leave the pot in a saucer of water.
• Feed: worm casting liquid diluted to weak tea colour, fortnightly in spring and summer.
• Position: the hottest, sunniest spot you have, out of summer storms if you can.
• Winter: move young plants under cover away from frost.

Germinating the seed

Caper seed is small, kidney-shaped and dark brown, about 3 mm across. For years the tough seed coat was blamed for its dormancy. A later study found that water does get in, and that the brake sits in the embryo. It is a shallow dormancy that a cold spell, time or plant hormones can lift. Seed left sitting in too much water also grows a jelly-like coat that starves the embryo of air, and a 12-hour rinse removes it.

With water alone, laboratory seed averaged about 14 per cent, and about 27 per cent when fresh, with half of those taking around eight weeks. An extension method of soaking, chilling and soaking again gave 40 to 75 per cent. Sow the whole 8-seed packet and expect one or two plants, perhaps more. Nurseries use gibberellic acid to push rates higher, but that is not a kitchen method.

More on these methods is in Soaking, Scarification and Cold Stratification.

When nothing comes up

• Given up too soon. Seedlings trickle up for two to three months, so keep the pots warm and moist for at least three. In outdoor beds, some seed comes up after one or two years.
• Too cold. Sown seed needs the warmth When to plant gives; in a cool room, move the pots onto a seedling heat mat.
• Too wet. Waterlogged mix brings back the jelly coat and invites rot; keep it moist, never soggy, and never let the surface crust.
• Chill bag dried out or went mouldy. Start again with a paper towel that is damp but not dripping.
• Old or warm-stored seed. Germination falls even after a month of storage; keep spare seed dry at 4 to 7°C and use it within two years.
• Sown too deep. Keep the next batch to the depth in Starting under cover, and no deeper.

Sowing Seeds

Start caper seed in pots under cover from treated seed, because seed sown straight into garden soil comes up far more poorly.

Starting under cover

• Fill 15 cm pots or deep trays with 2 parts seed raising mix, 1 part perlite and 1 part coarse sand.
• Sow treated seed 6 to 12 mm deep, two or three to a pot.
• Keep the pots in bright light and in the warmth When to plant gives, moist but not wet.
• Thin crowded pots by snipping the weakest seedlings at soil level with scissors, so the roots of the keeper are not disturbed.

Potting on and planting out

At 8 to 13 cm tall, move each seedling into its own 4 L pot with its soil still around the roots. Slip a clear plastic bag over the pot for a week, then open it a little more every week or so until it comes off. That is a form of hardening off (getting a plant used to open air and sun gradually), as hardening off seedlings explains.

Grow the young plants on in their pots through the first winter under cover. Before planting out, stand the pots in filtered sun for a week or so, then move them into full sun by steps. Plant them out in spring after the last frost, 2.5 to 3 m apart on a mound, and water them in well.

Care by growth stage

Water decides this crop: steady moisture for the first two summers while roots go deep, then very little. Feeding stays light, because capers are adapted to poor soil.

If growth stalls in very poor sand, a light application of controlled release granular (NPK around 14-5-10) in spring can help.

Cutting Back

The caper bush flowers on the current season's shoots, which start budding once they reach about 30 cm. A hard cut in winter, while the plant is bare, brings a strong flush of new stems each spring.

• Leave young plants unpruned for their first two years.
• From the third winter, cut every stem back to short stubs, or to the stump, in late autumn or winter.
• Remove dead and weak wood at the same time.
• Wear gloves and long sleeves on plants that carry spines under the leaf joints.

Companion planting

Pair capers with plants that like the same lean, dry, sunny ground, and keep them away from thirsty plants and brassicas.

Grows well with

• Thyme, lavender and oregano, which want the same hot, free-draining ground and little water.
• Olives, grapevines and almonds, which share caper plantings in Italy and Spain.

Keep apart

• Mint, whose need for constant moisture would keep the caper's roots too wet.
• Cabbages and other brassicas, which feed the same cabbage white caterpillars.

Harvesting Buds

Pick capers while the buds are still tight and closed, before any white petal shows, from the plant's second or third summer.

• Pinch or twist each bud off at its base with finger and thumb.
• Pick over the bush every 10 to 12 days through hot weather; the smallest buds are the most prized.
• Keep picking, because regular picking brings on more buds.
• Leave some flowers if you want caper berries, and pick those green and firm.
• Gather the tender shoot tips and young leaves too, if you want them.

Fresh capers and caper berries are too bitter to eat until they are salted or pickled. To salt the buds, mix them with salt at about 400 g per kg. Stir occasionally for 10 to 12 days, then drain off the liquid. Add another 200 g per kg, drain again after about 10 days, and store the buds in a jar under dry salt. Rinse and soak them in fresh water before use. Caper berries are traditionally soaked in salted water for a day, rinsed and kept in vinegar, and young shoots and leaves can be pickled too.

Follow a tested Australian recipe for any vinegar pickle, and top the jar up with at least half vinegar. Keep the jar in the fridge unless the recipe pasteurises it. Never store capers under oil without acidifying them first, and keep oil jars in the fridge: CSIRO explains the botulism risk. Salted capers suit sauces, salads, fish and pizza.

Traditional use and history

The English word caper comes from the Latin capparis, taken from the Greek kapparis. English speakers took the final s for a plural and dropped it.

Morocco and Turkey have been the leading producers and exporters. The IUCN assesses the species as Least Concern worldwide. Yet wild stands face genetic erosion from overgrazing and overharvesting, and much of the world's supply is still picked wild.

In Australia, a national rural research report studied whether Mediterranean-climate regions could farm capers, noting the crop had never been grown commercially here. Australia also has its own wild form. The Australian Plant Census lists it as Capparis spinosa subsp. nummularia, and Kew accepts it as a separate species, Capparis nummularia. It grows in Western Australia, the Northern Territory and Queensland, and feeds the native caper white butterfly.

Safety

Caper bush is sold as seed for growing. Nothing here is advice to eat or take any part of the plant beyond the kitchen uses above. Anyone thinking of using a plant should first seek advice from a qualified health practitioner.

Two unrelated weeds borrow the caper's name. Caper spurge (Euphorbia lathyris) has fruit that looks like a large caper, and its fruit and milky sap are toxic. False caper (Euphorbia terracina), a declared plant in South Australia, has a caustic milky sap that irritates skin and eyes.

Common problems

No capers in the first summer. Young bushes spend their first year on roots, so expect buds as Harvesting Buds describes, and full cropping from about the third or fourth year.

Plenty of flowers, few capers. Every flower is a bud that was not picked, so keep to the picking rhythm in Harvesting Buds.

Bare, dead-looking stumps in winter. Caper bush is deciduous and survives winter as a stump, so wait for new shoots in spring before digging it out.

Few buds on an old, woody bush. Buds form on new shoots, and an unpruned bush makes fewer of them, so cut it back hard in winter as Cutting Back describes.

Capers taste harsh and bitter. Fresh buds are bitter until salted or pickled, so use the method in Harvesting Buds before eating them.

Pests and diseases

Capers suffer few pests or diseases, and in Australia the main trouble comes from the caterpillars of white butterflies.

Caper white (Belenois java). This native butterfly migrates in spring and summer. Its dark brown to olive green caterpillars, dotted white and yellow, feed only on the caper family. Large groups can strip a bush bare, though plants normally recover. Pick off egg clusters and caterpillars, or net young plants during migrations.

Cabbage white butterfly (Pieris rapae). Its velvety green caterpillars chew holes in leaves and buds. Hand-pick them, net young plants, or spray a Bacillus thuringiensis product whose label lists herbs, at the label rate. Read more

Damping off (Pythium species and Rhizoctonia solani; Fusarium on caper seedlings). Seed rots before it emerges, or seedlings collapse at soil level soon after, most often in wet mix. Read more

Prevention first

• Cover young plants with fine insect mesh while white butterflies are flying in spring and summer.
• Check leaf surfaces for small groups of white to orange eggs and rub them off.
• Sow into fresh mix in clean pots, and water seedlings only enough to keep the mix moist.
• Clear away prunings after the winter cut, because caper white caterpillars pupate on their food plant.

Tips

1. Write the date the seed went into the fridge, and the date 65 to 70 days later, on the chill bag.
2. Save seed from ripe berries that have split open, with dark red flesh and dark brown seed, and sow it within a month.
3. From a good bush, take hardwood cuttings 12 to 30 cm long from one-year-old wood in autumn. Root them with bottom heat, as How to Take Plant Cuttings explains.