Wouldn’t it be great if everything went to plan in your garden? Perhaps for some it does, but certainly not for me. I like to think it would be boring for everything to go to plan and we are much better gardeners for having challenges, but perhaps that’s me feeling jaded? Over the last six years of creating my garden here at Mt Barker Springs, I have killed a lot of plants. Not deliberately of course, but they have died nonetheless. For the first few years it felt like I would plant two to kill one, but over the years my losses have reduced to less than one in five to one in 10, so I am winning. The plants that died succumbed to drought and a lack of water, wet feet in winter, frost, salty bore water, roos, bunnies, hares, or my own dog and flock of chooks, ducks and geese.
Even today whenever things go wrong I find myself being the garden detective, trying to work out what went wrong. Becoming a successful gardener is all about problem solving – looking at the evidence and investigating the motive or cause. The challenge is that solving the mystery often takes quite a bit of questioning and that is often a challenge when answering questions via email, letter or talkback radio callers, as there is often not the opportunity to gather enough information to solve the case.
Take the case of burnt leaves for example.
At the moment I have a number of plants in my garden with burnt leaves – ranging from butterfly bushes (Buddleja), weeping Japanese maples and even the Manchurian pear by my front door, and there can be so many causes of this.
Sunburn and underwatering is the obvious one however if plants are hardy and climate compatible they should not burn. If a plant is severely stressed for water on a hot day it may develop burn on its foliage. I have two plants with burnt foliage that I attribute to sunburn. My turmeric plants which are growing in a wicking bed – these don’t dry out as the wicking bed prevents it however having a large soft leaf and being a subtropical plants, the dry scorching heat of our 40 plus degrees days in full sun is simply too much for them. I try to cover the bed with shade cloth on the extreme days but one day it blew off. Hey presto, burnt leaves. Turmeric is herbaceous though and dies down over winter so it will not be damaged in the long term. The other is a weeping Japanese maple – firstly Japanese maples grow best in morning sun and afternoon shade or a sheltered sunny position, even though some larger trees with the more intact larger foliage may be seen growing in full sun in areas of the Hills when well once established and shading their own roots. The smaller and more dissected the foliage on these maples, such as that on the weeping varieties, the more readily they burn when in too much sun or when they are affected by hot north winds. I have a pot on my back deck which is under shade cloth but I wasn’t aware that it gets the late afternoon sun, and I let it dry out on a hot day, so again I have burn. It is deciduous so the burnt foliage will drop off in autumn and I need to take more care next year.
Sunburn is often able to be identified as it can occur more on one side of the plants than others, the side that corresponds with the hotter or western sun. Similarly if a plant is up against a corrugated iron fence, or up against paving, the growth closest to the fence or paving might be scorched from the reflected heat.
Overwatering. Believe it or not many plants develop what looks like burn on their foliage from overwatering and this usually happens in heavier soils over summer, when people panic and give plants too much water. Keep level headed about watering. Apart from thirsty plants in the veggie garden, most garden plants will only need at max a good soak once a week or so rather than every few days. Indoor plants often suffer from overwatering so if you have leaves browning off but not feeling dry and papery, make sure your plant is not standing in water in its saucer.
Fertiliser burn. This can occur when someone applies fertilizer at a stronger rate than what is recommended. Just because fertilizer works well does not mean that twice as much will have twice the benefit. On the contrary, it can burn your plant and result in burnt foliage. It often happens with people making their own worm juice, weed teas and liquid fertilizers from raw manures. It is far better to give your plants a weaker dose of these liquids every few weeks than a stronger dose less often. Diluting these home made brews to the colour of weak tea is a good rule of thumb that will not burn your plants.
Salt build up and salt burn. I use bore water on my garden as this is all we have and this water is salty. In the early days I killed some pots of camellias very quickly before I realized as they require acid soil and would have been best on rain water. Salts from the water can build up in the soil resulting in salt or lime induced chlorosis. The symptoms of this are plants with yellowing leaves with darker green veins. The green in a plants leaf is chlorophyll and this acts as the plants sunscreen so as soon as leaves yellow, they have increased risk of sunburn hence burnt leaves. Similar problems can show up near the sea when the salt laden air has the same effect on sensitive plants.
While some plants can tolerate salt in the ground, if salty water is sprayed on their leaves it can cause them to burn. For this reason, if you are using salty water it is better to water at ground level, ideally with drippers, rather than with sprinklers. This is sometimes easier said than done through as the salts can often build up and block the drippers and more vigilance is required to make sure the drippers are actually working. Similarly some people with salty bore water find that it clogs inline drippers (the brown dripper hose) within a few years.
I see evidence of salt burn in a number of plants around my garden like crepe myrtles as summer progresses due to the repeated use of my bore water. Fortunately our weather pattern is such that we get good winter rains and these flush the salts through the soil so that in spring when the deciduous plants come back into leaf there is no evidence of salt build up. I also notice that if we get a really good summer shower, the new growth that comes after the rains is clear of salt burn as the shower has flushed the salts through again.
Unknown causes. Sometimes though things go wrong that are just mysterious. The Manchurian pear by my front door has died on one side and each year in summer some of the leaves show an unusual discoloration and then burn on the tip. We cannot work out what is causing this and the tree comes back each spring looking fine. It almost looks like it is herbicide damage, yet we are organic gardeners. Perhaps there was something dumped there when the property was a ruin, who knows? Several times I have looked at removing the tree and starting again, but it is trying and still looks good from the front. Maybe time will tell and it will push through it, however I am prepared to just wait and see.
Each year in spring there are always some queries about weird growth appearing on people’s roses with deformed, twisted or stunted growth appearing in clusters with pale, narrow, twisted shoots that resemble coral or witches brooms. This pale growth will readily burn in the heat too as it lacks the chlorophyll to act as sunscreen. Typically it is noticed as they come back into leaf from their winter prune and it is a sign of herbicide damage. Roses are very sensitive to herbicide and if it is all affected, it often best to remove the plant and start again. If only part of the rose is affected, cut off these parts and feed with a seaweed based plant tonic and the plant may recover.
So next time you have a mystery in the garden, play detective and see if you can go through all the possibilities to solve the problem.