Predator Attracting Plants

Bellis 'predator' border, February 2012

Bellis ‘predator’ border, February 2012

Organic gardening isn’t conventional gardening, so why not enjoy some unconventional pest control?

Every garden is an ecosystem, comprising of plants, soil, fungi, bacteria and animals – including its gardeners. The plants we grow, and how we garden, can profoundly improve the way an ecosystem functions as much as the weather, or the time of year.

I think too much emphasis is given to so-called ‘pest-repellent’ plants. In reality, it’s easier to attract animals into your garden – they rarely wait for an invitation, so why not make a little effort to attract more of the useful ones?

Most food gardens have a little space that can be set aside to allow a few insect-attracting plants to flower away. For the past three years I’ve been trialling various ‘insectary plantings’, a fancy term for a mixed sowing of annual flowers, vegetables and herbs, and observing which of the flowers are most useful for attracting beneficial insects into my garden.

Organic gardening uses unconventional methods of pest control, and while I’m normally prepared to use organic remedies, like pyrethrum spray, to limit pest damage, during my trials it has been liberating not having to bother with spraying at all.

There have been surprises. Brahmi (Bacopa monnieri) is a medicinal herb which also makes an excellent flowering carpet. The blue-flowered form is very attractive to insects, in fact honeybees tried to pollinate them while I was planting them out! But its white-flowered alternative, which is very pretty, is distinctly less appealing to insects.

At sunset robber flies and dragonflies add drama to my summer predator border as they actively patrol it, swooping on dinner which they catch on the wing. But the best surprise of all has been seeing how unspoiled the basil sown amongst my predator border has been.

Ecosystem basics in a bug eat bug world

Grasshoppers and caterpillars are common garden pests. Left to their own devices, sometimes they can skeletonise crops, like winter crops of kale, and summer crops of basil. For the purpose of my trials I stopped spraying and reclassified these two pests as ‘predator bait’. ‘Bait’ like this helps predators to breed, but it’s necessary to provide food and shelter that suits predators for their whole life cycle, from egg to larva to adult.

This change in attitude – classifying pests as predator bait and plants as predator attractants – drives certain editors and sub-editors nutty. Fantastic! But every gardening audience I have spoken to gets it. Swan Reach Primary School (East Gippsland) pupils got it. So there’s hope for an organic future.

Some beneficial insects, like ladybirds, spiders, robber flies and assassin bugs, are predatory all their lives. Many adult native wasps are active caterpillar hunters since their larvae are carnivorous, but adult wasps only feed on nectar. At ‘Bellis’, the Euphorbias and Stapelia growing in the ornamental garden attract Tachinid flies and wasps, providing an ecosystem service I cannot replicate in the food garden.

I’ve had help identifying the more obscure insects from Dr Tim Heard, a Brisbane-based CSIRO entomologist. According to Tim, around 80% of all caterpillars never make it to adulthood thanks to native parasitoid Tachinid flies. Spare that swat – just like wasps, tachinid flies provide their young with caterpillars, but adults have no interest in visiting the kitchen – like wasps they’re nectar drinkers.

Satisfying these varied bug needs involves sowing or planting a variety of plants – ideally in a mixed border – so that they collectively provide nectar, pollen, accommodation and ‘predator bait’. The bigger the planting, the greater the reward. While managing the Royal Botanic Gardens, Sydney, I supervised seasonal sowings of a flowering meadow: 500 square metres of annuals and ephemerals. The result was spectacular. A living ecosystem emerged, complete with nesting Pacific black ducks at ground level to swooping welcome swallows. The public fell in love with the meadow garden, with its winding mulched footpath. In my time at the RBGS that was the only flower display to get us a double page centre spread in the Sydney Morning Herald.

Caring for your predator border

Ideally, find somewhere that receives six hours of sunshine, so that plants grow strongly and flower freely. Shelter is only important if you’re growing tall flowering plants, like giant sunflowers. Dig the soil over and rake the surface level.

If you’re sowing seed directly where plants are to grow, I find mixing the seed up first in a bucket with some dry sand or compost helps to make sowing small, fine seed more easy to handle and you get more even coverage. Sow in dry, calm conditions. Lightly rake the seed into the surface, then water well.

Keep seed moist during germination, which may take between one to two weeks. If you sow or plant thickly the extra foliage and cover gets things off to a good start. Remember to thin overcrowded seedlings, and to thin two or three more times as plants reach full size. Thinning improves air flow around plants, decreasing the chance of diseases, like mildew and bacterial leaf spot, plus it provides your first reward.

At ‘Bellis’ I have found that by mulching lightly (a veneer, 0.5 – 1cm deep) with chopped, leafy materials like sugarcane and lucerne, encourages egg laying by the black hairy flower wasp (Scolia soror). Common in mainland Australia, this wasp provides curl grubs for its larvae, burying them in egg chambers under this mulch.

Dead-heading, like watering, will extend the useful life of an insectary by promoting further flowering. Save seed later on, shortly before clearing the display at the end of the season.

Whatever you grow, aim to have two species of flowering plant at any season of the year. That’s dead easy if you’re a Seed Saver. By providing a reliable supply of food you encourage a variety of beneficials to become resident assistant gardeners, not just visitors. Most wasp species live reclusive, solitary lives, but I allow native social or ‘paper wasp’ species to build their nests amongst garden plants. My rule is nesting wasps must not interfere with garden upkeep, upset my pets, or the postman.

Cool season sowing

For sowing during autumn and winter, try: Alyssum, brahmi, wall rocket (Eruca sativa), borage, calendula, dill, parsley, queen Anne’s lace, lettuce, mizuna, poppy, Johnny-jump-up, fennel and wallflower.

Of all the spring flowering plants, the one with the most predator-attracting flowers is Italian flat-leaved parsley which also produces the most prolific and long lasting displays of any plant I have trialled so far.

Warm season sowing

For sowing during spring and summer, try: Cosmos, basil, Chinese spinach (Amaranthus spp.), love-lies-bleeding (Amaranthus caudatus), spider flower (Cleome spinosa), sunflower, salvia, pumpkin, radicchio, horned melon (Cucumis metuliferus, but beware, this can be rampant), single-flowered dahlia, flame nettle (Solenostemon scutellarioides), gomphrena and bells of Ireland (Molucella laevis).

Of all the summer flowering plants, the most enticing I’ve found are coriander and flat-leaved parsley. Like Brahmi herb, triple curled parsley is almost useless but, so far, flat-leaved parsley is the best all round predator attractor. Normally gardeners grumble when their coriander flowers, as this means harvesting their leaves will soon end. Get over it. That’s your cue to sow more. Last spring I counted 23 different beneficial insect species visiting my coriander flowers. This record has been beaten by flowering flat-leaved parsley ‘Giant of Italy’. I gave up counting. Even CSIRO experts haven’t been able to positively identify every species my parsley encouraged. In my (evolving) opinion, you can never have too much of  allies like these.

This slideshow requires JavaScript.

Predator attracting plants grown at Bellis

Edible crops

Bok Choi, Brassica rapa var. chinensis
Broccoli raab (aka flowering turnip) Brassica rapa var. rapa ‘Cima di Rapa Quarantina’
Chervil, Anthriscus cerefolius
Chinese cabbage, Brassica rapa var. chinensis
Chinese cabbage, Brassica rapa var. pekinensis
Chinese celery, aka smallage, Apium graveolens
Chinese spinach, Amaranthus cruentus
Chinese spinach, Amaranthus tricolor
Chinese spinach, Amaranthus tricolor ‘Flying Colours’, ‘Flaming Fountains’, ‘Joseph’s Coat’
Chives, Allium schoenoprasum
Choko, Sechium edule
Coriander, Coriandrum sativum
Dai Gai Choi, Brassica juncea var. foliosa
Dill, Anethum graveolens
Dwarf Greek basil, Ocimum minimum
Endive, Cichorium endivia
Ethiopian cabbage, Brassica carinata ‘Old Women Meet and Gossip’
Finger lime, Citrus australis
French marigold, Tagetes patula ‘Himalayan’
Green amaranth, Amaranthus viridis
Japanese parsley, Cryptotaenia japonica
Kale, Tuscan, Brassica oleracea Acephala Group
Kohl rabi, Brassica acephala Gongyloides group
Lettuce, Lactuca sativa
Love-lies-bleeding, Amaranthus caudatus
Mizuna, red-leaved, Brassica juncea var. japonica
Mouse melon, Melothria scabra
Mustard, Brassica juncea
Parsley, flat-leaved, Petroselenium ‘Giant of Italy’
Phillip Island hibiscus, Hibiscus insularis
Pigeon pea, Cajanus cajan
Podding radish, Raphanus caudatus
Pumpkin, Cucurbita moschata
Radicchio, Cichorium intybus
Radish, Raphanus sativus
Sacred basil, Ocimum tenuiflorum
Sweet basil, Ocimum basilicum
Tatsoi, Brassica narinosus
West Indian gherkin, Cucumis anguria
Wild rocket, Diplotaxis tenuifolia
Winter melon, Benincasa hispida

Predator attracting ornamentals

Andean Silver-leaf Sage, Salvia discolor
Brahmi, Bacopa monnieri (blue-flowered only)
Clustered mountain mint, Pycnanthemum muticum
Euphorbia caerulescens
Euphorbia cyathophora
Euphorbia graminea
Euphorbia griseola
Euphorbia splendens var. splendens
Kalanchoe orgyalis
Rondeletia amoena
Sansevieria suffruticosa subsp. longituba
Stapelia gigantea
Stapelia leendertziae

Jerry Coleby-Williams
13th September 2012