Since we have just completed our main weeding programme at Wirrapunga, I thought an article on weeding may be useful. To understand the problems with weeding it is necessary to understand a little about weeds.
Fifty years ago the land that is now Wirrapunga was a cow paddock. However it had not been cleared or pasture improved so it had a fair sprinkling of indigenous plants. The cattle introduced other grasses and when the cattle were taken out about 25 years ago, introduced woody weeds such as broom, blackberry and pine trees gradually became dominant.
When I arrived on the scene 15 years ago the introduced woody weeds were the dominant plants, followed by introduced grasses and then a sprinkling of remaining indigenous plants.
So! if we looked at just one square metre of land it may have contained one broom plant and little else. However! if we had looked within the soil we would have found many seeds. It is an understanding of these dormant seeds that is imperative if we are going to successfully develop a bush garden.
Since seeds can remain dormant and viable in the soil for over 50 years, it would be helpful to know what grew on that one square metre over the last 50 years to know what seeds were in the soil. These seeds are waiting for the right conditions to tell them to germinate. If they do not find the right conditions they gradually become unviable.
If we assume that about 20% become unviable each year and there were no replenishment then if there were 10,000 seeds of a certain species in our square metre one year then there would only be one left after forty years. We could assume that after 50 years all seeds of that species were gone.
On the other hand, it seems that if conditions are right for germination about 40% of viable seeds germinate. If therefore, a plant of a species is able to grow it will quickly replenish its soil seed bank.
If we then go back to our one square metre that contained the broom plant, the soil under it would contain, say, 10,000 viable broom seeds. Since fifteen years ago before the broom plant took over the one square metre it was probably covered with introduced grasses, the soil would still retain some 350 viable introduced grass seeds. Further since about 30 years ago there were indigenous grasses on our square metre, there would still be about a dozen viable indigenous grass seeds waiting for their opportunity to germinate.
So! we destroy the broom plant and are left with one square metre of bare soil stocked with seeds, mainly broom seeds, waiting for just this moment. After the April rains we would expect something like 4,000 broom seedlings, 150 introduce grass seedlings and about 5 indigenous grass seedlings to appear.
Of course this is a gross simplification but I think it would convey the idea. It is at this stage that many people make a fatal mistake. It is those 5 indigenous seedlings that make up the treasure we are seeking. It is also probably their last chance because if we make an error now the indigenous soil seed bank may be too small to give us a second chance.
Most gardeners now only see the broom seedlings which is quite understandable. We had one broom plant. It has now been replaced by thousands. Of course if we wait then most will die and it will gradually become just one again. But by then our indigenous plants are gone. If we just concentrate on the broom seedlings then the introduced grasses will smother the indigenous ones and again they are lost. There is a temptation to just spray the lot and start again.
The only real answer is to carefully remove all the broom seedlings (all 4,000 of them) and all the introduced grass seedlings (all 150 of them) and allow the 5 indigenous seedlings to flourish and rebuild their soil seed bank. Then, and only then, they are relatively safe for another 30 years.
Then, of course, the next year you will have 1,500 broom seedlings and about 60 introduced grass seedlings to remove. But that will be easy now you know how.
This is why it is imperative to only start what you can finish. So often people get stuck into their weeds only to be confronted with ten times, or even 100 times, the work the next year. Many give up. This is demonstrated by the paddocks of weeds throughout the Adelaide Hills. Unfortunately most give up any idea of having a bush garden and instead have one of those other sorts of garden instead.
The important result of a weeding programme is to remove all unwanted plants before they produce viable seed. How long you have after the seedling appears depends on the variety of plant. Annual plants don't bother building much of a root system. They germinate soon after the April rains. They start flowering in about September. They set seed in December. Of course the exact timing depends on the season. This year (2009) we had a break on cue in the last week of April, a good rainy season and an abrupt end in the middle of October. On the other hand perennials spend the first season putting down a good root system so they can survive our long, hot, dry summer. Perennial grasses normally seed in their second year whereas many woody weeds will only seed in their third or fourth year.
It is much better to leave that broom bush where it is for another year or two than to remove it and not be able to finish the job. On the other hand, of course, it is imperative to get your bush garden functioning as soon as you can. We are very quickly losing our beautiful bush plants. I suggest that you start your bush garden of about one are - that is 100 square metres. Unless you have been cultivating weeds by half heartedly trying to remove them, the first year will be easy. But don't be fooled into a false sense of security. See how you go. Always start your weeding at the same end so that if you don't finish then you have finished some anyway. If you finish your allotted area early then increase it slowly.
There is no doubt, in my mind, that a bush garden is the most rewarding. It is certainly not the easiest. However the rewards are great. It is during the annual weeding that I do my stock take. This is where I must carefully look at every plant in my bush garden. This year the orchids had increased tenfold. Three indigenous species, new to my garden, appeared. These were the tiny spider orchid, Caladenia minor or lady's finger, the tiny pennywort, Hydrocotyle callicarpa and a wahlenbergia which I have called the Wirrapunga Bluebell which seems to be an un-named species with 3 or 4 petals.
Of course there is also left, at the end of weeding, that wonderful pile of weeds that we recycle, by composting, through our vegetable garden which means we can be self sufficient with our vegetables without the need of any fertilisers or manures whatsoever.
Happy weeding!