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Archive for April, 2012

A frequent cry from gardeners relates to lack of flowering and very often the response is to add potassium. But potassium is NOT responsible for flowering, any more or less than any other nutrient and the real reasons for flowering problems can be many.

No flowers at all? Ask yourself how old is the plant? Is it a seedling which may not flower and fruit for several years? Many eucalypts are in this category. I have an Illyarrie (E. erythrocorys) which is now seven years old and hasn’t yet flowered – I’m not happy but there’s not much I can do about it! Passionfruit from seedlings are similar and may not fruit for several years.

Sometimes pruning is the problem. Particularly with fruit trees, cutting off the wrong wood means no flowers and no fruit. Pears, plums and cherries produce fruit on spurs, lateral growth is often minimal. Japanese plums fruit on 1-3 year old spurs. European plums fruit on lateral spurs on 2-3 year old wood. Peaches and nectarines produce fruit on the new season’s fruiting wood. Apples produce their best fruit on fruit on wood two-years and older, though some varieties such as Sundowner™ also bear fruit on one-year wood. Figs produce their main crop on current seasons growth and an early lighter crop on the previous years wood.

Sometimes the weather is responsible. A cold snap at a critical time can prevent flowers from initiating or abort them very early. Drought can do the same. Occasionally plants don’t flower because the light hasn’t been right. Some plants such as Zygocactus will not flower if their night time darkness is interrupted by light from a street light or inside a house.

The mechanisms for flowering in plants can be complex and are generally a combination of temperature and daylength and one of these may be more important than the other. So anytime you grow a plant out of its natural habitat, you run the risk of problems depending on how pernickety it is. Banksia coccinea is one plant like this that tends to not flower well, if at all, around Perth. Banksia coccinea is also prone to the ‘pruning effect’ because it actually is initiating the next years flowers around the same time as it is flowering. So prune after flowering and you’re apt to be pruning off all the next years flowers!

It needs to be understood that flowers may have quite separate requirements for flower initiation as compared to flower development. Obviously flower development can’t happen without first having flower initiation but you can have flower initiation and no flower development afterwards. Most European bulbs require a period of chilling during winter to initiate flowers but the soil temperature during spring can also be too high and those flowers will abort. Conversely, many South American or South African bulbs that are autumn flowering have high temperature requirements that must be met for flower initiation and flower development to occur. Sometimes these requirements can be met by other means such as putting bulbs in the fridge for a few weeks but sometimes this doesn’t always work well because of these other factors at play.

Sometimes uneven flowering or flowering on one side of plant can happen and that’s usually for the same set of reasons as above.

Poor nutrition is seldom responsible for a complete lack of flowering, although excessive nitrogen can keep a plant vegetative. Poor nutrition though, can be responsible for some peculiar flower development such as no petals/empty flowers. Calcium or boron are most often the culprits when there are fruiting or flowering problems but first check for periods of water stress because interruptions in the transport of these nutrients can be the reason. Both calcium and boron are essentially immobile (so when in short supply they can’t be moved from older leaves to places of greater need) so that is why symptoms are seen on the growing tips and why symptoms of deficiency show up in flowers/fruit or any growing points (in palms death of the growing point will kill the plant). Bent neck (should be self explanatory) is usually a calcium problem but often more to do with water stress/periods of reduced transpiration such as high humidity) rather than actual lack of calcium in the soil.

Sometimes flowers go green (gerberas show this symptom). This is usually due to infection by a mycoplasma and is incurable. Get rid of affected plants.

Occasionally flowers go mad and start producing flowers within flowers. Or whole little plants within flowers. Usually this sort of secondary development is physiological and due to erratic weather conditions. Rarely is it due to herbicides or any other chemical agent. I have seen this on banksias, roses and carnations to name a few.

You may have flowers but they remain stubbornly closed. This is often wind damage – we call it blasting. Sometimes, it’s also disease such as grey mould caused by Botrytis cinerea.

Finally, you may have had flowers but they may have aborted or dropped for some reason. And depending on when that happened, it may not have been that evident. Most often this is due to moisture stress or a sudden increase in soil salinity (either because the soil dried out temporarily or because you threw on a heap of fertiliser). Some plants also have inbuilt mechanisms for controlling flower (and hence fruit) load to ensure that all fruit set can fully mature. All cucurbits are like this (pumpkins, melons). Other fruit trees can be biennial bearing – that is they tend to have one year when they crop heavily, the next year is a lighter load.

While we are talking flowers in this blog, don’t forget the importance of pollinators where fruit is concerned. Bees, flies, moths or other insects. Lack or, or poor or uneven pollination can also cause a range of problems from no fruit to malformed fruit. But that will be a whole other episode!

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I covered the question of growing plants from seed or cuttings in another blog. Now I’d like to explain a little more about how to grow plants from seed.

Germinating seed can be as simple as scattering some seed on the ground or in a pot and Voila! It all happens. But often its not that easy and in fact can be down right frustrating. Why?

Well there’s a whole heap of factors that affect seed germination. If you’re buying packaged, branded seed such as vegetable seed then you can be fairly sure the seed will germinate provided its not out of date and you haven’t killed it! You see seed doesn’t last forever – although some lasts for many years, some species need to be germinated within about 12 months of being harvested because viability drops off really quickly (viability means it is capable of germinating ie the embryo in the seed is still alive).

Seed storage
For most seed of most European varieties, keeping the seed in the fridge is a good idea but recent research with many Western Australian species has shown they need to go through a process called after-ripening and that means room temperature storage is best. And when you think about it, Western Australian species are not used to going through a period of winter chilling so that sort of makes sense.

Other requirements and treatments
Some species require light for germination and so you should not cover the seed while it is germinating. This includes species such as lettuce and many other small seeds. Many hard coated seeds such as Acacias need to be scarified in some way – dropping them in boiling water is the easiest way but sandpaper can also be used. For larger seeds nick the seed coat to allow moisture in. Some seed contains inhibitors in the seed coat that have to be leached out. That can be done under running water. Nature does it over winter in the rain. Often seed may be dropped in acid to help it germinate – this is just another form of scarification. As is passing through the digestive tract of an emu, bird or other animal!

There are also a number of other specific chemical treatments that may be used on seed. For example priming seed with potassium nitrate often helps germination. Sometimes hormones can be used (gibberellic acid for example). If you have collected the seed yourself then there are a number of other considerations. Was the seed harvested at the correct stage of ripening? Is the seed even viable ie does it have an embryo and is that embryo mature? Many native plants have a large degree of seed predation – insects may bore into the seed and eat part of the inside. Most of this can be answered by cutting the seed open and examining it under a magnifying glass.

If you’re a native plant lover then you’ve probably heard of smoke treatment. There are certain compounds in smoke that help trigger germination in native plants. Extensive work has been done on that at Kings Park in Western Australia and also in South Africa. Both these places have plants that have evolved in an environment prone to bushfires.

If you’re having trouble germinating something, here are some references for you. And always try a search on the internet for your species, you may be surprised at the amount of research work out there that has been done.

http://www.backyardgardener.com/tm1.html

Australian seeds: a guide to their collection, identification and biology By Luke Sweedman, David Merritt, Kings Park and Botanic Gardens, 2006 CSIRO Publishing

Ball Culture Guide: The Encyclopedia Of Seed Germination by Jim Nau, 1999, Ball Publishing.

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