Archive for January, 2011

Got a phone call last week about some tomato plants. In fact we had some leaves brought in. They looked pretty bad. To me it seemed that they had run out of water at some stage – big sections of totally brown dry scorched leaves. But apparently that wasn’t the problem! There was mottling. And the person concerned was adamant they wanted them testing for disease. Actually that was the first message I got. There was something bizarre and unknown wrong with these plants and they had to be tested. I took one look and assessed it was poor management. Had a long discussion with the owner of said plants. In the end we got someone to look at them – I mean physically, actually look at them. I was vindicated. Hardly any fertiliser, inadequate watering and under 90% shadecloth. Which brings me to another enquiry I also had last week. Which also turned out to be largely inadequate watering leading to pollination problems.

What am I saying? Always look at the basics. The sort of weather we’ve been having lately brings huge problems for growers and home gardeners. Even if you can keep the water up to the plants they may suffer. And it doesn’t always matter that you’re growing with heaps of compost etc etc as many of these home gardening network people do. If you think you can grow good veges on 2 waterings a week in this weather you need a reality check. Right now on days with 40 degrees you have commercial guys out there watering up to FIVE times a day so they can get reasonable crops off with no problems. Things like blossom end rot which is a calcium problem, is generally due to fluctuations in the plant water status. Because calcium is immobile, its movement is dependent on the plants transpiration stream, in this weather, any blip in its water status can cause problems. And any blip in soil moisture, at the same time causes another blip in nutrient uptake because all nutrients have to be taken up in soil water – they need to be dissolved, so general growth suffers as well.

Weather which is 40 degrees one day and 20 the next can causes huge problems. Same as sudden downpours of rain. Try as they might, plants can’t always regulate their hydration as well as they need to. So one minute they’re working hard to suck all the water they can. The next minute they have an oversupply and have to wind it all back. And what do you see? Fruit splitting. And sometimes even leaves split. If you ever see warty/corky little spots on leaves that can be oedema. The result of a leaf trying to offload excess water and not quite getting there.

So in this weather we’re having at the moment – expect problems. Having a look at the daily evaporation figures can be quite enlightening. Here is a live weather station at the Department of Agriculture at South Perth. There is a network of them all over the state. If you scroll down and look at the past week, you can see that evaporation has gone from 2.7 to 10.7 in the space of a few days. I’m willing to bet you haven’t touched your controller! And you wonder why your plants are having problems :-).


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Well there can be a myriad of reasons why plants aren’t growing but often it comes down to the simple things – water and fertiliser. This could be a bit of a free ranging post but lets see where we go today.

Lots of people have no luck with veges. Especially leafy ones. For them, feeding in the first 2-3 weeks is really important. It doesn’t have to be much – if they’re out of a punnet then 50mL of liquid feed like Aquasol (some widely promoted products aren’t fertiliser by the way) each will more than do them – no need to saturate the whole ground, if there’s no roots there it will just leach out. And you can do that up to 2-3 times a week until they get bigger. Then swap over to a granular fertiiser like NPK blue applied in the root zone once a week and you’re right. Growth lost in that first few weeks is never made up later. Lettuce grown slow will be bitter, celery, woody.

In older areas around the Perth metro area, nematodes are common. Most often they are root knot nematodes. Pull up an old tomato plant, any nightshade in the garden even dig around a poorly performing rose bush and if there’s little knots on the roots, chances are you have nematodes. They take food and water from the plants so they suffer. They are really hard to control – commercially we use nasty chemicals that are not available to the home gardener. Its often said sugar will work and the principle is fine but really its not practical for treating a large area. Really, the best avenue is either rotation with a non host plant ( such as any grasses incuding sweetcorn) or you can solarise your soil (google soil solarisation, there’s a few references out there including a farmnote from the Northern Territory). That is a way of pasteurising soil or potting mix using the heat of the sun. Its take time and effort but does work and doesn’t kill off the good bugs.

If you have a plant thats not thriving its always a good idea to have a dig around the roots. The number of times I have leaves brought in to me when I really need roots and soil is about 20:1. You may find the soil is completely dry down below. You may find knots on the roots. There are also nematodes that don’t produce knots (lesion nematodes). In that case you will just find a really odd pattern of root development – very profuse, tufty. You may find your plant is being strangled by its own roots. Have a scrape at the collar of the plant – is it rotting at ground level? Did you pile mulch up around it or is it top heavy and getting buffeted by the wind? Is there evidence of new white roots or are the roots stripping – ie if you run your finger down the outer layer sloughs off. Root rots can also be common but in many cases they are really a result of unfavourable environmental conditions and treating with fungicide won’t work – you need to fix the base problem. That doesn’t have to be waterlogging it can be fluctuating soil moisture levels. When soil moisture goes up and down a lot, any fertiliser in the soil solution will also go up and down in concentration a lot and may burn roots. Once roots are damaged disease jumps in.

So bottom line – if you have a plant that’s not thriving or dying always consider all aspects of its care, especially how its been watered, recent weather etc. Don’t assume a disease is the primary reason, often its only the result of poor management. And yes that means you, however unpalatable that may be! Always look for the simple things.

By the way – I kill plants too – I’m not immune from doing silly things, or forgetting to do something so don’t feel too bad about it!

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OK, today I’m going philosophical on you. I’m tired of being told repeatedly that people want simple messages, that their eyes glaze over when you try to explain anything in words of three syllables or more.

Horticulture is not simple! Gardening is not simple! It is a craft to be learned. Experiences gained build on each other and add to our knowledge over time. We are dealing with natural systems. We do not completely understand them. In most cases you cannot apply a formula, a one size fits all approach. What is it about society today that everything has to be dumbed down to the level of a five year old. Or worse. We see it on TV. In magazines. The messages we are supposed to consume are an insult to our intelligence. Where is our pride? Our sense of achievement in accomplishing something? In overcoming the odds? In doing something no one else has done. Or in simply doing something DIFFERENT. Not being a sheep. Not accepting what is dished out to us simply because it is there!

Horticulture is in dire straits, I believe, because of this attitude. No one appreciates the skills involved in growing a plant. The level of knowledge required to grow a good crop of broccoli, tomatoes, oranges………….The predilection of educational systems to simplify everything down to a level where any idiot can pass isn’t helping. This is why we’re getting students coming out of medical school that have never worked on a real corpse in anatomy and therefore can’t identify major landmarks in the body! Do you want such a doctor operating on you?

So it is in horticulture. The decline in funding for research and development isn’t helping either. I know how it was 30 years ago and how it is now. Add to that the increasing disconnect between country and city dwellers and any appreciation for where our food comes from and the skills involved in growing it are all but gone.

So I ask you, in the light of this how can we expect those that work in horticulture to command respect and to earn a good salary when there seems to be a popular view that any bozo can do it!

Natural systems are complex. Ever changing. I have seen the tussle that engineers or accountants turned horticulturalists have had. Many fail. No, you can’t apply a generic formula. You can’t factor in inflation every year – yields won’t go up by 4% per annum (don’t laugh I have seen it)! There is this annoying thing called the weather. We are largely at the mercy of it – ask any grower in Carnarvon or Queensland at the moment.

So I ask you to bear with me. I do try and explain things simply. But they are complex things and so many factors play a part. Look upon it as a challenge.

Horticulture is one area where you can be learning every day. Its health benefits are numerous in terms of being meditative, a stress release, a form of physical activity – keep that bone density up, those Vitamin D levels.

Reap the benefits of being able to eat fresh healthy food with known inputs of chemicals and pesticides. Have fresh flowers in the house releasing their essential oils instead of plug in vaporisers made from synthetic chemicals with all manner of attendant health risks. Above all have pride in yourself and your accomplishments.

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Sub-surface irrigation

I’ve been promising something on sub-surface irrigation and here it is!

The flavour of the month these days is sub-surface irrigation, everyone’s talking about it, especially in these days where we need to use water efficiently even more than ever.  But like most irrigation systems there are situations where it is suited and those where it is not!  Sub-surface irrigation is commonly said to achieve great water savings and be highly efficient.  But being installed underground, ‘out of sight out of mind’ means the temptation is there for householders to turn it on and leave it running – and that doesn’t save water!

For garden beds, normal drip irrigation is actually just as efficient and if installed above ground where you can see it, at least it’s a bit harder to put a spade through the lines when you’re planting!

Really there is nothing wrong with properly installed sub-surface irrigation under lawns.  But it can be costly to install.  When operated off the scheme water you must install a RPZ backflow prevention device if you are injecting any chemicals into the system at all – and that includes herbicides to stop root intrusion into the drip lines, or fertiliser.  And that makes it quite an expensive exercise for a small lawn.

I hear you saying – herbicide – you mean chemical!  Yes.  You really do have to put herbicide through sub-surface or roots will find their way into the emitters and block them – a bit like tree roots and septics.

You also need good filtration for sub-surface irrigation because otherwise emitters will block and apart from the fact the first sign you see might be a dead plant, its hard to unblock them when they are buried!  Good ongoing maintenance is needed for subsurface systems to work properly.

The Irrigation Association of Australia has a Waterwise Garden Irrigator Program and installers accredited under that program have to adhere to a certain set of guidelines.

The other reason why subsurface may not be as efficient as its made out to be is when you have a garden bed with large shrubs you are to a certain extent constrained by the dripline as to where the water comes out.  So if the emitters are 30 cm apart there may be soil in ‘no man’s land’ getting water that need not.  Yes, you have some flexibility in terms of where you run the lines themselves but the emitter spacings within the line are fixed.  And you need to install the lines thinking ahead in terms of what the garden will be in 5 or 10 years time.  Sub-surface can’t be moved around or added to like above ground drip.

There is a compromise system now – sub-surface mulch.  Which is really drip except it used the same inline drip materials as subsurface.  Which brings us back to the risk of being blocked by ants.  And refer to my other posts on mulch as to the issues of using mulch.

What you need to think about is where you need the water and in what quantity.  And at what rate can you apply it in your soil before it whizzes down past the root zone.  Remember that in our sands, water may only spread laterally about 20 cm each side of a dripper and it may go down past the root zone in less than 20 minutes if it has a relatively high flow rate.  The trade-off with having low flow rates is you need really good filtration or you get blockages and watering times will need to be longer which can be expensive if you are running a bore.

To summarise:

Advantages of subsurface irrigation:

a. Everything’s underground so no more mowing off of sprinkler heads in the lawn!

b. There is the ability to apply fertiliser evenly through the irrigation.

c. Highly efficient way of watering lawns.

Limitations of sub-surface irrigation:

a. High set-up cost in many situations if installed correctly.

b. Hard to see exactly where the water is going and whether there are problems with emitters.

c. High risk of emitters clogging by penetrating roots and sucked soil particles.  Ongoing maintenance required – once problems occur they may be hard to fix.

d. Can still get water repellency in sands leading to preferential pathways and water going past the root zone.

f. May need overhead or supplementary watering during the establishment phase.

g. Being only 15 cm below the surface you can’t dig with gay abandon!

h. Inflexible with respect to design over time.

i. Prone to damage by rodents.

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