The key to the successful growing of Proteas is to observe where they grow in the wild. Proteas do not grow in excessively damp areas (over 3 m of rain per year) nor in hot humid areas (greater than 80% humidity with temperatures over 30°C for several days). If your garden does not experience these conditions, then you can plant most proteas. The exceptions are those high altitude species which require mist and cold for much of the year.
Proteas benefit most by being well exposed to summer winds, but cold winds with frosty conditions are lethal. In sheltered spots, heat build up can be lethal. Most species are moderately resistant to frost, but young plants will need extra protection. This can be achieved by watering plants or shading them overnight (allowing for adequate ventilation) when frost is expected.
Soil is far more important than climate. Many proteas grow only on soils which are very poor in nutrients. Many garden soils contain large quantities of nutrients which either poison proteas or speed up their rate of living, thus shortening their lifespan and making them susceptible to disease. Proteas can be grouped into four categories based on their soil requirements: sand-lovers, clay-lovers, lime-lovers and peat-.
Sand-lovers: The majority of proteas grow on very infertile, sandy soils with a pH of less than 6 (ie. very acidic). Deep sandy soils, on which few garden plants will grow without expensive soil preparation, are thus perfect for these species. However, with enough water these proteas will grow on most soils - unless phosphate levels are too high. Sand-loving species produce specialized proteoid roots (resembling fine bottlebrushes) which are ultra-efficient at absorbing phosphorus and nitrogen from the soil. These roots cannot function under alkaline conditions, and alkaline fertilizers (e.g. those containing nitrates) weaken plants. Similarly, lime or bonemeal should never be applied to these species. Fertilizers containing phosphates are lethal, as the proteoid roots are too efficient and absorb lethal doses. Therefore avoid NPK or nitrate fertilizers. Low quantities (5g/m2 per year) of ammonia fertilizer (which is acidic) are suitable, and will provide any nitrogen required. Mulching is best undertaken by putting an acid mulch (pine bark, pine needles, leaf litter from oak or acacias) on the soil surface, without disturbing the soil.
Clay-lovers: These proteas are more tolerant of soil conditions and are thus easier to grow, as they behave more like the classical garden plant. It is still advisable, however, to avoid nitrate and phosphate fertilizers and to use acidic mulches.
Lime-lovers: Proteas preferring alkaline soils may grow in crevices in solid limestone. These species can be grown on sandy or clay soils if lime or calcium is added to make the soils alkaline. However, these species tend to be tolerant of acidic soils, and pH is not critical. They are thus easy to grow in any garden. No research on fertilizing the lime-lovers has been undertaken to date, but it is probably wise to avoid nitrates and phosphates.
Peat-lovers: Proteas growing in black, peaty bogs - usually on the south slopes of mountains - prefer soils very rich in organic matter. This can be achieved by mixing copious quantities of acidic organic matter (preferably sterilized) into the soil before planting. Once planted, the soil should not be disturbed subsequently. By keeping conditions acidic, drainage should improve and the production of poisonous nitrates should be suppressed. Note that the boggy conditions enjoyed by the plant are not equivalent to waterlogged soils: in nature water in bogs is continuously moving underground and thus provides oxygen to roots, which standing water cannot do. Good drainage is thus essential.
Most proteas require copious quantities of water. Heavy watering is essential to keep a low pH (ie. an acidic soil) and to prevent accumulation of salts. Water should be acidic or neutral in pH, not alkaline (except for lime-loving species), although salty (brak) water is tolerated.
Watering should reflect the natural times at which specific proteas experience rainfall in their habitat. Thus watering for species from the southwestern Cape should be emphasized in winter, in summer for Natal and Transvaal species, and all year round for species from the southern Cape. Do not forget, however, to lightly water plants out of season as well.
Soils must be very well drained, as waterlogging prevents roots from obtaining sufficient oxygen. Proteas are particularly susceptable to waterlogging, and the only worse treatment is too little watering. Drainage may be enhanced by planting on steep slopes, elevated terraces or rockeries, or by using drainage ditches or drains. Other tricks may be used, but avoid placing drainage stones at the base of the pit when planting. This does not enhance drainage to a sufficient depth for most proteas, which, with the exception of the superficial proteoid roots, have deep tap-root systems.
Once established, most proteas should have their taproots deep enough to reach the water table. However, this requires that you plant proteas from your area. They can then be allowed to grow naturally, without requiring additional water other than rain.
Fertilizing and soil care
Lawn can be grown between between proteas, or ground-covers (including many proteas) can be used to prevent weed growth. Never scarify or dig in the soil closer than one metre from a protea bush. This destroys the proteoid roots near the surface, liberates undesirable nitrates from the mulch, and spreads fungal and bacterial diseases such as Phytophthora. Mulching is best done by merely placing acidic vegetable material (pine, oak or acacia leaves or bark) on the top of the soil. Protea gardening is thus relatively maintenance free.
NPK (nitrate, phosphate and potassium) and alkaline fertilizers must be avoided. Phosphate is especially poisonous. Phosphorous toxicity results in yellowing of young leaves, leaf drop and blackening and dying of shoots. Calcium (as bone meal or lime) may also be lethal to sand-, clay- and bog-lovers.
Potassium may be given if plants show signs of deficiency: margins of old leaves turn pale and die back, resembling a scorched leaf, and plants appear stunted. Potassium is best supplied in the form of potassium-chloride. Nitrogen may be required if older leaves turn pale green. Always supply nitrogen as ammonium, never as nitrate. In both cases a recommended dosing rate is 5 g per m2 per year, spread out in even doses throughout the year.
Pruning and cut flowers
Picking flowerheads from Proteas is equivalent to pruning them (except in the case of some long-stalked Spiderheads). This is because flowerheads are not produced on long stalks, but on the branches of the plant. Picking for flower arrangements requires long branches, which may result in the removal of many leaves from the branch and thus the plant. New branches produced from cut stems originate from buds which lie in the stem above the leaf stalk. Since these buds die off in old branches as they lose their leaves, cutting into old wood will kill the stem and weaken the plant.
Although overpruning will weaken your plants, judicious pruning will result in more flowerheads being produced the following year, increase the lifespan of the plant, produce a more rounded and neater shrub, and will prevent diseases from infecting dead wood. By removing flowering buds (deheading) before normal flowering, it is possible to delay flowering in Leucospermum by up to two months without weakening plants. Beware however, as deheading after the normal flowering period will result in vegetative shoots and no blossoms.
Pruning is best done after the flowering season has finished. Cut each of the stems with the most recent growth to about 100 mm long. If cuttings are desired, then it is best to prune later in the season after the current year's growth has hardened and the leaves have fully expanded.
Plants with lignotubers should be treated differently. These species are adapted to survive fire by having their buds in underground stems (called boles, rootstocks or lignotubers). Thus while fires burn off all the above-ground branches, the underground stem with its buds remains safe. The loss of the branches stimulates dormant buds and rejuvinates the plant. Heavy pruning, ie. removing all the branches by pruning them off at ground level, every 5-20 years will rejuvinate any garden species with a lignotuber, and result in a new crop of flowers. Do not try to simulate a fire and burn your bush - your fire could be too hot and kill the lignotuber. In these plants flowers should be cut with as long a stem as possible (right down to the rootstock) in order to stimulate new buds to grow.
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