Green things need small amounts of boron to function properly; it is necessary for completion of a plant's calcium cycle. If you have boron-poor soil, your plants may do well with a bit of added boron, which they can get from borax. However, borax may provide too much boron and inadvertently kill the plant. Beer has a subtler amount of boron and has phosphorus, potassium and selenium, other nutrients needed by plants. In addition, beer can stimulate microbial soil activity. Fertilizing with beer and borax together requires a light hand but may help your plants greatly.
Determine whether your soil needs boron. The best way to do this is to send a soil sample to a testing lab.
Determine whether your plants need boron. The kinds of plants that most need boron are cabbage-family crops, strawberries and some root vegetables like beets and carrots. Bean plants do not like much boron, so hold off if you are growing beans.
Mix 1 tbsp. of borax with 1 gallon of water.
Put the mixture into a watering can and give each plant 1 fluid oz.
Wash out your watering can.
Make a beer fertilizer by adding 1 cup of Epsom salt, 1 cup of beer and 1 cup of ammonia, in that order, to 2 cups of warm water. Ammonia adds nitrogen to your homemade fertilizer, and the salt helps aerate the soil. Avoid inhaling the ammonia fumes.
Pour this mixture into your watering can, and sprinkle it around the base of your plants.
Repeat the beer treatment every few weeks if necessary and the borax treatment only once every three years.