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Growing Proteas from Seeds
"Would you be able to tell us how to propagate some Protea seeds that we found at the top of the Soutpansberg? "
Doug Norval
Growing proteas from seeds is really quite simple. (see PAN 4.16 for details). The three steps are:
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Proteas have two main strategies for storing their fruit.
Serotiny
Storing the seeds on the plant for a fire. Most Sugarbushes and Featherbushes and half of the Conebushes store the fruit on the plant. This strategy is ideal for growing proteas from seeds.
Getting fruit: Most of these species flower in winter, but the fruit need only be ripe in time for the summer fires. These species thus require about six to nine months to ripen the fruit. Furthermore, fruit are nourished while on the plant, and in theory should last for many years. In practice, insects find them tasty, and many heads are empty after a few years. However, once taken off the plants these fruit rapidly lose their viability: after all, in nature they must germinate after the first rains or else they will be gobbled up by rodents.
In practice this translates to two things: To get viable fruit, do not pick seedheads from this year - always pick the seedheads from two or three years back (further back and the insects will have had their fair share). Having collected your seedheads, you now need to get viable fruit. For Conebushes it appears that most fully-formed fruit are viable. However, Sugarbushes provide "dummies" to fool any rodents which try to eat the fruit. In Protea lepidocarpodendron, for instance, George Bailey claimed to get, on average, a single viable fruit out of each seedhead: the highest ever was 17, more often he got none. Now with 140 flowers per flowerhead, this means 1 fruit in 140, or a 0.7 per cent seed set ratio. Other studies have got twice this for the same species, so that the mean seeds per flowerhead probably varies between areas and between years. So look for fruit that are fat, but pliable. Of course, rodents are not stupid, but nor are proteas, so don't be fooled by the fruit that are fat and hard - they have nothing in them and will not germinate. A bit of practice will allow you to figure out the viable fruit.
Planting fruit and cueing germination: To grow serotinous species, add water and wait. Many will germinate within a few weeks, but some may require a "cold shock." This will come with the first winter rains. So autumn is the best time to sow serotinous seeds in the Cape, which means you should collect the fruit in late summer. In the seed trays, merely sprinkle the fruit on the surface and perhaps add a few mm of sand to anchor them in. In the wild most germinate on the soil surface. The hairs and wings will orientate the fruit for maximum water uptake from the wet soil.
Myrmechochory & Therochory
Soil-stored fruit - safety from fire and predation.
All Pincushion-allies, Spiderhead-allies and half of the Conebushes (those that release their fruit - see PAN 6.9) rely on rodents (22 species) or ants (180 species) to bury the fruit underground where they are safe from predation. A further 30 species probably fit into one of these categories. This strategy poses all sorts of problems for the propagator.
Getting fruit: Because the fruit are often collected off the bushes by ants and rodents, it is often difficult to obtain fruit. The best strategy is to bag the old flowerheads and return some time later to extract the fruit. Beware, do not collect fruit that is not yet ready for release - the flowerheads must start disintegrating! What happens is that the fertile fruit expand to full size and appear ripe, but the plant delays the allocation of nutrients to these fruit (and in doing so protects them from predation!) to the very last minute. Immature fruit appear hard, but are merely filled with a watery substance and will simply rot. If you use the bag approach, you can be assured that almost every well-rounded fruit is a viable one.
Planting fruit: Now comes the secondary problem - preparing the fruit for storage. In ant-dispersed species, the ant-fruit is an oily body which will rot and may result in fungal attack of the fruit. This must be removed before you attempt germination. In the seed beds the oily body may also stop germination cues from reaching the fruit, thus hindering germination.
Unlike, the surface fruit of serotinous species, these species must be buried underground. Not too deep, about 1-5 fruit diameters should be sufficient. If they are buried too deep then they may not perceive the germination cues, or those which do germinate may be too weak to survive. These species grow a "foot" (PAN 6.13) to anchor them in the soil as they push their way to the surface. In addition, it appears that a proportion of these seeds do not germinate in the wild after a fire, but get "carried over" in the seed bank to the following fire. Thus germination rates are seldom above 80 per cent.
Cueing germination: These fruit may survive for many decades underground (35 years for the Marsh Rose (PAN 8.5), 60 years for the Silver Tree (PAN 20.10), being among the records to date). The problem then, unlike for serotinous species, is telling these fruit that it is time for them to germinate.
It appears that when protea seeds are underground they fill up with water and dry out with the soil. There is no point in germinating with adult plants to out-compete you, and lots of rodents waiting to gnaw your tasty cotyledons (the seed leaves in which all the nutrients are stored). The ideal time to germinate is after a fire, as all the adults plants will have been killed. The rodents will have been killed by the fire, eaten by owls and hawks (as there is no cover for them to hide in), or starved to death (as there is no food). So the fruit stay put and wait for the post fire environment. Only then will they germinate. And if you do not provide just such an environment, then they will slumber on, and on, in your seed trays.
What cues are needed? Lets first look at the fruit. After a few years they are starting to get a bit worn. The hard outer coats are starting to disintegrate and be attacked by fungi. We can mimic this by lightly sandpapering the hard outer coats, or even giving an acid treatment (any acid for a few minutes to hours depending on its strength). Those fruit in ants nests will be slowly eroded by the formic acid. The effects of these treatments will be to allow more oxygen to reach the seeds. But these are all just primers, not cues. What cues can the seeds use to time their germination?
There are two constraints. There is no point in germinating unless there is a fire. And there is no point in germinating unless it is autumn or early winter. Germinating too early (after an early February or March shower) may result in seedling death if the following rains take too long. Germinate too late and the plants will not be able to establish a tap root to the water table before the summer drought. Thus we need two cues - one to get germination going, and the other to time it. Of course the cues may be one and the same.
The entire story has not been worked out in detail, but the following cues are important. After a fire:
- The ant's nest dies and the acidic, carbon-filled atmosphere is replaced by a more neutral, oxygen-rich one;
- The soil is no longer is covered by a blanket of plants - exposed to the elements, it may heat up to over 60oC during the day and may fall close to freezing at night. This cycle will continue until the vegetation cover is re-established, provided that the fire was hot and did not leave too much debris;
- The fire, in consuming the plant matter, covers the ground with smoke, ash and charcoal.
We can mimic these processes by making sure that the seed trays are exposed (not under shadecloth or trees or in hot houses), that the soil is wet but not waterlogged, and is a coarse sand, neither clay nor too-humus rich, and by providing smoke extract.
The weight of evidence, for proteas at least, is that a cycle of 10-20 days of soil temperatures exceeding 20oC during the day, and dropping to below 10oC at night, while saturated with water, is the trigger for germination. Exact details vary among species, and among localities within a species, and probably among any seed crop at any locality. Commercially grown cultivars tend to produce fruit with the least stringent requirements, whereas wild fruit may not germinate if night-time temperatures are merely a few degrees above the threshold. Inland populations probably require colder nights and hotter days than coastal populations.
We can thus predict that in the wild most fruit will germinate in autumn following a fire, earlier or later depending on when the first large cold fronts move through. This is probably also the time that most will germinate in your seed trays.
Establishing your seedlings: Once the fruit have germinated, they will do two things simultaneously. The cotyledons will be lifted and expanded to capture light and start providing energy and carbon. The tap root will anchor the plant (serotinous species) and start heading for the water table which may be many metres below the soil surface.
Marie Vogts has some photographs showing that by the time a Protea cynaroides has produced its first two real leaves (not the seed leaves) its roots may be more than 1 m down in the soil. Similarly a one week-old seedling may have roots 50-200 mm long. This is probably true of most proteas - by the time summer arrives the roots must be within the water table, else the plants will die. This probably explains why many sandy plains in the Cederberg are devoid of proteas, the summer water table is simply too deep down for proteas to be able to reach it before the summer drought. Winter waterloggin probably exacerbates the problem as the roots do not grow in waterlogged soil, but must grow as fast as the water table subsides. Restios, the only plants to thrive under such conditions, survive by going dormant - a complete shut-down - in summer.
This poses a real problem for the gardener. If you want your plant to establish immediately you must transfer it to the garden before the first true leaf is developed. However, if the area is not ready for the plants or if you wish to protect it from slugs and other seed-leaf feeders, you may wish to put it into a temporary pot or bag, until it is a bit bigger. Of course, 2-4 m high pots and bags are nor readily available - so this will mean that the plants roots will be stunted. This will further mean that you will have to water the plants through their first few summers. Keep the seedlings in full sunlight. If they are placed under shadecloth they will usually need a hardening-off period in full sun, before planting out.
Watering plants through the first summer is not a major problem, as most gardeners know. Usually one has a reasonably established garden and one wants to plant in a few additional plants. Under these conditions, the plants will need summer watering anyway to help them establish between the competing plants. This watering will usually allow the plants to catch up to their wild cousins and outperform them within a few years.
If your garden is new and you are planting the beds (do not dig over, merely remove the grasses and unwanted shrubs without disturbing the soil too much) for the first time, try planting the fruit directly into the bed. Do not use a mulch as this will inhibit the germination cues to the fruit.
Beware the bane of protea growers: Phytophthora root rot. Provided your soil is well drained, only a few unfortunate plants will succumb. But allow any free-standing water near the seedlings or establishing plants, or disturb the soil, and the fungus Phytophthora will proliferate and fatalities may be high. This is also the reason for not disturbing the soil too much.
Avoid fertilizers too. If the plant has deficiency diseases (yellow young leaves), use an ammonium-based fertilizer, which is totally free of Phosphorous (P) and extremely low in Potassium (K).
Have a look at Gardening Tips and Resprouting and Growing Proteas in Your Garden and Stats on Seeds in Flowerheads.
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