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Boron deficiency in passionfruit causes flower drop, while searching for the ratio to add Borax to my plants I found a number of sites with interesting things to say about the use of Borax.  It is a very versatile product and googling it shows you can use it everywhere from the laundry for washing clothes, to entertaining the kids by making crystals...  Below are some of the gardening uses mentioned.

Weed Control

Borax is most commonly used in organic gardening as a means of weed control. A solution of borax and water is a good way to kill unwanted plants in your yard and garden.

The trouble with borax is that it can kill other plants or make them sick as well as getting rid of the plants that you don't want. You need to be careful to use the right borax amounts for organic
gardening. In this case, that means a quarter of a cup of borax
dissolved into a gallon of water.

Spray a good coating on the plants you are trying to get rid of. This method is particularly popular for creeping Charlie. If you are eliminating weeds from your lawn you might want to fertilize once the weeds have died to encourage new growth in your lawn.


While borax is known for killing a lot of plants, there is one plant that apparently benefits from the application of borax to its soil: sunflowers. According to GardenWise
magazine, watering sunflowers with a mixture of water and borax helps
increase the size of blooms and seed production by up to 20 percent, as
well as making the plants stronger. They advise that plants should be
watered with a half teaspoon of borax mixed in a gallon of water when
the buds are about halfway developed and again a month later.

They also mention that borax can be used to help preserve flowers. Just dip the flower in borax, let it sit for a day and then tap off the excess borax.

Some people also suggest the use of borax to get rid of insects and other unwanted creatures. Unfortunately, because its tricky to get the right amount of borax that will kill the pests but not the plants, this method of insect removal
is not recommended.

Dissolve 25grm borax in a little hot water and make up to 600mls adding cold water. It will kill greenfly on roses and other plants.When applied to the stems of fruit and other trees, it destroys all insects
in and about the bark. and clears blight on apple trees. Brush the
solution in this case or a spray will probably do the job.The powder
may also be sprinkled on places where infested with insects, black
beetles, etc.

A very little in the garden iffin you get clubroot in your brassicas.

Determine if your soil needs a Borax fertilizer. You can send it to a soil testing center to find out. "B" stands for boron, the element you get from borax. If you are short then
continue making the fertilizer.

Decide if the plants you are growing need boron. Beans do not, and they won't like it if you fertilize them with Borax. However, cabbage-familly pllants, strawberries, carrots and beets all appreciate boron.

Mix one tablespoon of Borax with one gallon of water, and pour into your watering can.
  1. Apply one fluid ounce of the Borax fertilizer to the base of each plant.
  2. Repeat only once every three years.
The basic ratio of Borax to soil should be one tablespoon to 100 square feet. Keep this in mind.
Too much Borax will easily kill your plants, so be careful!

Has a comprehensive list of how to identify boron deficiency on each type of crop.

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They say:
Mix one tablespoon of Borax with one gallon of water (3.8 litres), and pour into your watering can.
Apply one fluid ounce (29 ml) of the Borax fertilizer to the base of each plant.

Can someone please check my math on this conversion! I am not going to apply 30ml to each plant!

1 tab/ 3.8L = 30ml
1 tab/ 8L = 60ml
1/2 tab/ 8L = 120ml
1/4 tab (ie 1 tsp)/ 8L = 240ml
1/2 tsp/ 8L = 480ml
1/4 tsp/ 8L = 960ml

So rounding things (less is better) if I add 1/4 tsp to a 8L watering can I can give each plant 1L of the solution?
As I recall, Borax is a bit toxic. Erring on the side of caution with where it's used and how much could be a good idea.
Gee, I like to do things the hard way! Hubby got home yesterday and after I spend ages explaining to him my calculations he said - 'why not make up half the original mixture and put into a 2L bottle, then when you need to add 30mls to a watering can and use it that way'


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