Journal of the Australian Native Plants Society Canberra region (Inc)
The invisible seedbank
By Roger Farrow
June 2021
The recent drought (1998-2020) decimated the plants in our garden area as we eventually ran out of dam water for supplementary watering. The rains finally arrived in late February 2020 as Australia’s climate pattern entered a La Nina phase. Heavy falls continued throughout winter saturating the soil and filling the dams. It arrived too late to revive many of our shrubs, some trees and many herbaceous plants.
However, in spring 2020 something remarkable happened: seedlings started emerging throughout the garden area along gravel paths, the side of the driveway and in the mulchcovered beds. Some seedlings came from plants that were still alive, others from plants that had died in the drought in the previous year, others from plants that had been absent for several years and finally some were from plants that have never grown in the garden. Here I am talking about native plants but of course there were many exotic species germinating as well, the ‘weeds’, such as Briar Rose (Rosa canina), Blackberry (Rubus fruticosus). Sow Thistle (Sonchus asper), Fleabane (Conyza bonariensis), Mullein, Verbascum thapsus, Spike Cudweed (Gamochaetus coarctata), and Cranesbill Geranium (Geranium molle) among others.
parvifolius
unfortunately exotic: Geranium molle
SHRUBS
The commonest seedling emerging in the pebbles in the driveway was Veronica perfoliata, shown in the title. The parents of these plants, growing in neighbouring beds, had died during the drought so the seed would have been one or more years old. Many of these plants were successfully transplanted or potted up. Their seeds are very small and are not normally used for propagation but it was an easy task to dig these plants up and transfer them into tubes ready to plant out in more suitable locations.
Several Grevillea ‘poorinda’ hybrids were planted in the garden area and along the driveway in the ‘80’s’. Many have matured and died over the years and this accelerated during the recent drought. A few have thrown hybrid offspring over this time. Remaining old specimens along the driveway were removed in 2018. Hundreds of Grevillea seedlings have now emerged from these parents in the litter in this area, the first to ever germinate there for at least 2 decades. I have potted about 50, perhaps something spectacular will appear.
Another Grevillea, G. asplenifolia also died in 2019 from the drought. It was more than 20 years old. About 20 seedlings appeared last spring for the first time below where it grew. As it was the only specimen, it must have selfpollinated. Its principal pollinator in our garden is a bird, the Eastern Spinebill. All the specimens were successfully transplanted into pots.
In the same area I had a female Gynatrix pulchella growing. In the wild, this requires moist conditions and it succumbed to lack of water and competition from Pomaderris shrubs much earlier, in about 2015. Large numbers of seedlings have now appeared where it grew at least 5 years after its death. Most of the pomaderris also eventually succumbed to the recent drought .
Over the years, Correa seedlings have emerged in gravel below their parent plants in small numbers. This accelerated last year including a few of seedlings of Correa lawrenciana that had died in the drought. Most Correas proved to be very drought resistant, especially C. glabra and some cultivars of C. reflexa.
A not so welcome native that has suddenly germinated in large numbers in the garden area is Kangaroo Apple, Solanum aviculare. These were grown from seed from the Lake George provenance more than 30 years ago. A few plants and their offspring have struggled over the years. However, this season they have proliferated like triffids (does anyone remember John Wingham’s novel the Day of the Triffids, also on film and TV) growing to over 2 metres in height in 4 months but finally met the axe when they threatened to overwhelm much of our garden. Its seeds are dispersed by birds that eat the fruit such as Silver-eyes and King Parrots.
I have several mint bushes belonging to about 6 species but only two have produced seedlings, namely Prostanthera ovata and P. incisa. The latter died early in the drought in 2019 but the P. ovata have proved very drought tolerant.
Some years ago, I planted two species of the two local Clematis species grown from wild-collected seed. A single C. microphylla has survived climbing high into a brittle gum. Two C. aristata started climbing but both eventually died about 5 years ago. This summer seedlings of both species have proliferated, especially C. microphylla, that has now threatened to smother other shrubs in the garden and most of them are now being removed except for where they can climb.
Native Raspberry, Rubus parvifolius is another plant proliferating in the gravel paths where it is not wanted. Its seed is almost certainly passed through birds. Some shrubs did not mass produce any seedlings following the rains although they appear to have had good seed production. They include Crowea exalata, Kunzea ambigua, Leionema lamprophyllum X, and Philotheca myoporoides, among others, although several of these have produced an occasional seedling in the past.
FORBS
Among herbaceous plants that have suddenly reappeared include the shortlived Pelargonium inodorum that has been absent for more than a decade. Its ally, Pelargonium australe, is a great survivor here and produced more seedlings last year in new areas than in the past. Its seeds are wind dispersed. I have had a Rock Isotome, Isotoma axillaris, growing in a pot for several years and it produces seed every autumn. Last spring seedlings suddenly appeared in the gravel for the first time and were flowering by summer.
Some unwelcome plants proliferating in the garden were Houndstongue, Cynoglossum australis, with its hooked seeds that burrow spontaneously into socks, and Cockspur, Plectranthus parviflorus, that was a small plant confined to a wet spot but has now spread everywhere, overwhelming other native plants.
A ground cover that has proliferated from the seed of existing plants after the rains and is very welcome, is the Creeping Saltbush, Einadia nutans. Single plants may cover more than 1 square metre and grow from a single taproot. The everlasting, Xerochrysum bracteatum, has also appeared but its origins are unknown since it does not resemble any of the selections and hybrids that have been grown here in the past, and resembles the wild form that grows along nearby roadsides. Its seeds are wind dispersed and may travel some distance from their source.
The take home messages from these observations is that droughts and the drought breaking rains that follow, are necessary factors in the renewal and regeneration of many native plant species. In addition, the seeds of many species can survive for a number of years until conditions suitable for germination occur.
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