Archive for July, 2011

Why talk watering again I hear you say, its winter, its raining? Well I was out in my garden weeding yesterday and I can tell you the soil is still dry about 50 mm down in lots of places. I am about to plant some shrubs today and I know that I will have to be super careful and not get lulled into a false sense of security.

Why? Well firstly the plants are in the standard pinebark potting mix used by many nurseries, that is quite porous and will dry out quite quickly. The plants are used to being watered regularly. Secondly where I’m planting is close to our bush and so there’s a lot of built organic matter on the top of the soil, almost 50 mm of it and it is that which is so highly water absorbing and therefore taking up most of the rain that is falling. The same as a thick layer of fine mulch will do. So what I will do is dig fairly deep and wide – deeper and wider than the root ball, and mix this layer thoroughly with the soil and water thoroughly before I plant. That way, when it next rains, hopefully the water will penetrate further than it has been so far and my plant will be OK. But still watch the root ball itself and make sure that doesn’t dry out.

Always consider the disparity between the medium you are planting INTO and the medium the plant is in as you bought it. If you buy vege/flower seedlings, for example that are in a fine medium with very high waterholding capacity, then unless you keep the sand around them quite moist continually, those roots won’t have much incentive to move out into the surrounding soil. You know, the first thing commercial growers do when they plant seedlings is pour on the water to get the roots growing and moving out and thus supporting the plant both physically and from being able to take up nutrients from a wide area. I’m not suggesting you need to pour on lots of water because in sand that’s a waste – it drains easily and doesn’t move laterally. But you need to try and keep a small area round that seedling damp most of the time. That is why drip is ideal for that purpose. But it is always a balancing act. If you keep the environment close to the plant too wet all the time that can create an ideal environment for diseases such as root rot or even grey mould. We see most root rot in summer when its hot. Warm nights and frequent watering are part of the cause.

So what about the rest of my garden? As I’ve been out weeding and digging I find that things are far from homogeneous. I have patches that are wet quite a way down and patches that are clearly non wetting. And why might some of this be? Think about it carefully. You may have been watering faithfully all summer when it was hot. Then we got a few decent falls of rain. Then we got to July and were told to stop watering. But plants don’t stop using water. And as you’ve heard me say many times, our coarse sands doesn’t store water so if there’s no rain for, say a week, you may well be in trouble. Particularly if that plant had responded to the rain by starting to grow again and therefore is using more water.

The other strange thing that sometimes happens in autumn/winter is salt burn from fertiliser. Especially if you’ve been using drip and therefore there is a confined wetted zone around the plant. What happens is that the fertiliser you put on all summer gradually accumulates around the edge of that wetted zone. Then when you get rain, it can push that salt into the plants root zone and that can cause problems. It doesn’t always happen, it depends on the shape of your wetted zone and how much rain you get. But it is something to think about.

One last word. We ARE in a crisis with regard to water supply in Perth. We cannot keep using water at the current rate. Desal is not the answer, imagine what that does to the ocean over time. Do think about your garden, what you plant in it and most of all when you have your retic on, check your sprinklers. So often when I’m out running in the early hours I see broken sprinklers gushing away and sprinklers turned round watering roads and paths. Retic needs constant maintenance make sure you do it. And don’t go out and buy the cheapest pop-up you can find. Irrigation is designed for a reason. If you replace your sprinkler make sure its the same brand or at least has a similar output in terms of flow, coverage etc. That way you won’t be wateirng for twice as long as you should just to accommodate the bits not getting the coverage from the sprinklers that they would have if designed correctly!

OK, that was more than a word. Sorry. See you next time!


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Since a large part of my life is spent in problem solving I thought I’d run through some of the things I see a fair bit of around Perth and what you can – or can’t do about them.

We get a lot of calls about leaf spots, especially on roses. People often bring me in a leaf or two or three and ask if this leaf spot killed the plant. My answer is usually no. Its not often that leaf spots will kill plants. Sometimes however, the leaf spot may be an indication that the plant is not happy and may be suffering in other ways that could end up killing it. But not for roses. I don’t spray my roses for leaf spot. Its so hard to manage to keep on a protective spray at the times that they are likely to become infected ie when its wet/humid/showery. And endless spraying does result in the disease organisms becoming resistant to those chemicals over time. It’s even happening with copper. Better to try and find varieties that aren’t so susceptible to eg black spot. And practise good hygiene – remove diseased leaves for example.

There are a couple of cankers causing widespread problems around Perth in Eucalyptus species. Quite a lot of work is being done on them at Murdoch University. You can see sap oozing out of the diseased areas on the trunk. I believe drought stress is one reason the problem is so bad. The other is very likely the widespread practice of spreading uncomposted mulch. Particularly when its from dead/dying trees. There is nothing registered for its control. Trunk injection with phosphite is about the only current treatment that can be tried. Many of these cankers are endophytes – that is they live in the tree and normally don’t cause any problems. But when any sort of stress sets in they cause disease. Plants are so much like humans – they also have an immune system and immune responses and when they are ‘down’ they get sick just like we do.

A while back I was invited to look at a dying acacia tree in someones backyard. I was told the problem was the decreasing water table. Unfortunately the holes and the sap oozing from the trunk and branches told a different story. Acacias are very susceptible to borers and this was what was killing this one.

If you are having persistent problems with a particular disease in your garden think about alternate hosts. Particularly where vegetables are concerned. There are many diseases, including viruses of tomatoes and capsicum that can be kept going all year round by the presence of alternate hosts. Tomatoes, capsicum, eggplant, potatoes and chillies are all Solanaceous crops and there are a number of weeds and other plant species in the same family such as nightshade, petunia, Nierembergia , Physalis and Brunsfelsia that can also carry some of the same diseases. That is why it’s important to rogue out errant potato plants that come up. These plants can act as a reservoir of infection for your next crop since many viruses are spread by leafhoppers, thrips and aphids. Seed can also be a source of infection so do not save seed from infected plants. Unfortunately, these insects can fly long distances so while you can keep your own backyard clean, you have no control over anyone’s elses! Commercially this is a major issue since many of these viruses are devastating and there is no cure, only prevention. The only way they can often be dealt with is by all growers in a designated area having an agreed rest period where the affected crop is not grown.

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This is one area that is so highly pertinent at the moment yet there has been so little definitive work done on it. Much of the information around is anecdotal.
And as I said in previous post, there is a tendency to assume that all native plants are frugal with water yet this is not the case. All native plants were not created equal. Moreover there are many places in the world that have as much or less rain than Perth and their plants are equally well adapted to drought.

One way plants adapt to low rainfall is be annual in nature. Their lifecycle is during the rainy period – autumn, winter and spring. Many bulbs fall into that category. And not all bulbs require chilling. There are a huge array of bulbs such as nerines, hippeastrum, gloriosa (considered invasive in some places), liliums, freesias, gladiolus and clivia that don’t need chilling. Any bulb which flowers in autumn doesn’t need chilling and some of the spring flowering ones like some of the narcissus also don’t require much chilling.

There is actually a very comprehensive list of the drought tolerance rating of landscape species put together by the Californians, you can download it from here and it contains quite a few Australian species.

Many palms aren’t that low in water use being classed as moderate so don’t expect your palms to prosper without watering. The good old box tree that you see planted all over the place is also a moderate water user. Coming from Queensland that’s hardly suprising! So one might ask why are we planting it as a street tree? Two other commonly used street trees are also moderate water users – the Chinese tallow and the good old plane tree. Given, they are chosen for other reasons, like their ability to be hard pruned, resistance to pollution and root compaction but if we are to plant them we need to make allowance for their water use and relative intolerance to drought. Most conifers are moderate water users and we’ve also been noticing many Norfolk Island pines around Perth all burnt from the afternoon sun on that side of the trunk.

There are many plants that will survive quite well on 40% of evaporation – and that includes the much maligned lawn. The moderate water users I’m talking about require around 70%. High water users such as ferns need around 100%. There is also a world of difference between what plants can survive on and what they may look good on! But also bear in mind that many of our northern sandplain species undergo a sort of summer dormancy, in contrast to European plants that have a winter dormancy. So they tend to look their best in spring which is when they often flower and after that they hunker down for the long dry summer. Its really annual behavour in a perennial plant!

Plant water use is not all about the total amount of water required. Its also about WHEN they need that water and that can be the most inconvenient part of it all! Citrus trees are classed as moderate water users, needing about 70% of evaporation. But they are sizing up their fruit right through summer when its hottest and they also have quite shallow root systems so they need plenty of water over summer. They do benefit from mulching to keep their roots cool and moist but be careful. If you create a nice fertile organic layer on top of the soil, by virtue of the fact that it IS on top of the soil, it will be most prone to drying out. Roots in that zone will have to be well cared for by irrigating more than once a day in summer to keep the soil moisture (and salt content) of that layer steady. Citrus are also flowering and setting fruit in winter/spring when an ill-timed bout of frost can totally destroy the crop for the coming year.

Slightly off topic is the matter of plants with variegated foliage. They don’t do well in full sun. They burn easily – so that includes many of your variegated conifers as well as variegated Agonis and Ficus. And I hope you never, plant Ficus in your garden. They have extremely invasive root systems that hunt out septics and raise footpaths and paving at the drop of a hat! Pots are fine – just not in ground.

So, getting back to plant water use. This last year in Perth has been tough on plants. Huge numbers of Eucalyptus and Casuarina in the bush or as street trees have been keeling over from the double whammy of little rainfall combined with falling water tables. And while we are getting good falls of rain right now, don’t expect our plants, or our groundwater levels to recover fully. The trend for rainfall in Western Australia is all down for the last 100 years and its not epxected to change I’m sorry to say. But I still think its possible to have a good garden, you just have to be a bit smart about it. Trees and greenery are important for helping keep the environment cool, as a habitat for birds and other fauna and for our sanity! I don’t know about you but I couldn’t – and wouldn’t live in a concrete jungle.

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