Greetings @shag,
As promised, I dug into the archives here and pulled up what I could regarding Gibberellic Acid (GA3).
My personal experience with it is modest and I havenāt found a reason to return to using it. I originally purchased a packet of GA3 to try and germinate some very old and rare āLandraceā seeds from Vietnam. That was successful, at least to get the seeds to sprout and show the first real leaves, but none of the seedlings showed enough vigor to be worth growing out. Stunted and sickly. I only used the GA3 in the water to soak the seeds, I didnāt spray it on the seedlings.
I also attempted to stimulate growth on a healthy plant but all I got was an unhealthy plant.
My take home message was that only the lowest concentration had the desired effect without damaging the plant. Typical recommendations for dilution are in the 250 - 500ppm. I came closest to a positive outcome at 100ppm.
If I were to use GA3 again, it would be as a potential substitute for STS as a sex reversal tool. Iād stick with 50-100 ppm because I donāt think that level would hurt the plant as a foliar spray, and Iād keep spraying daily until I saw balls or got bored.
And that is the extent of my personal experience with GA3. For completeness Iāve added below the best article I found on the subject.
Cheers,
-Grouchy 
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FARMING WITH AN OLD TECHNOLOGY THAT COPIES NATUREāS BASIC FORMULA
by Edward DuQuette
Iāve written and taught on the subject of farming and alterative growing techniques for quite a few years now. Aquaponics has always been my favorite subject to elaborate on. Aquaponics, and its close cousin Hydroponics, both have endured a wave of criticism and praise. But when itās all said and done, both technologies have proven themselves over and over again as successful means of growing larger and more desirable fruit and vegetable products. So whoās the new guy in town, whatās the newest growing technique? Well first of all itās not new; the developed process has been around for over 50 years and the bases of this process been around since the first plant popped its way through the soil. When I first heard of it about two years ago, it sounded too simple to be true.
Making it Easy
As an engineer, I love to unravel technology to understand it. As a teacher, I love to take what Iāve learned and teach it to others, and as a writer, I love to present it in written text to excite experimentation. In Japan around 1935, a hormone was found as a result of a plant condition that caused plants to grow much taller than normal. The condition was called āfoolish seedling ādisease, and after many years of research, this natural occurring plant hormone was identified as Gibberellic acid or GA3. The direct benefits of GA3 are that it helps regulate plant growth, rapid seed germination, and plant resistance to cold and disease in almost all vegetable, fruit and flowers. Where does Gibberellic acid come from? Itās a natural product extracted from the Gibberella fujikuroi fungus that is found on rice plants. There are many forms of gibberellic acid with GA3 proven to be the most effective.
Gibberellic Acid is a white powder; it can be purchased in 2.0-5.0 grams packaging. Larger quantities are also available, but for initial experimentation the 2.0-5.0 gram packaging is the most economical. A little GA3 goes a long way and because of its involved manufacturing process it is not cheap. You will also need a new unused plant sprayer, isopropyl alcohol 70%, distilled water (or filtered water) and a source of music.
Dilute the GA3 powder; the GA3 powder is very hard to dissolve just by stirring in water alone. Proper dissolving can easily done by adding very small amounts of alcohol to the GA3 being used until the powder is dissolved (this very small amount of alcohol will not hurt your plants). The dissolved powder than can be added to the distilled water to produce the proper PPM dilution. (See chart below) Also recommended is the addition of a wetting agent; a few drops of agriculture soap can be used.
It is very important to remember proper PPM dilution rates for success. Too much GA3 or too little can affect your end results. The GA3 needs to be applied in early morning before sunrise if possible. Bright sunlight will effect GA3, making it less effective or destroying its effect completely. Only mix what youāre going to use that day. The powder can spoil in high heat and will only last about one week once mixed. Wrap the unused powder container in aluminum foil to protect from direct sunlight. If stored in a cool, dry place, the powder can store for up to 2 years. Do not freeze or refrigerate.
GA3 Powder 90% is soluble in 70% common rubbing alcohol. Before it can be used is must be turned into a liquid. The amount of Gibberellic acid that needs to be used is very small. Drop the correct amount of powder in a small bottle, then add a few drops of rubbing alcohol. The only reason to use alcohol is to dilute the Gibberellic acid powder. Use just enough alcohol to wet the gibberellic acid powder. If after a couple of minutes you can still see some powder, add a few more drops of alcohol. Then just add water to get the right concentration. It is often said that alcohol will damage plants, but not in the very low concentration needed to dissolve Gibberellic acid. 90% GA3 powder will not dissolve in water.
You donāt need much of the solution to soak your seeds, just enough for the seeds to fully swell. Most seeds can be soaked in the small poly-bags. Tiny seeds should be folded up in a filter paper for ease of handling when soaking. Larger seeds can be soaked in a pill bottle or small jar.
To know the concentration, replace X and Y, (X mg / Yml) x 1000 = Z ppm
To know the amount of solution to make to get a certain ppm, replace X and Z, (X mg / Z ppm) x 1000 = Y ml
To know the quantity of powder to use, replace Z and Y, (Z ppm x Y ml) / 1000 = X mg
For example: 100mg of GA3 in 200ml of water gives you 200ml at 500 ppm (part per million). 100mg of GA3 in 400ml of water gives you 400ml at 250 ppm. 1g of GA3 at 90% concentration will be supplied as a powder in a small ziplock bag, sufficient quantity to make 2 liters of solution at 500 ppm. You should have enough for a couple of years.
Use strong solution, 500 ppm, on very hard to germinate seeds; and a 250 ppm on seeds that are just hard or slow to start. Seeds enclosed in a hard coat may be submit to a higher concentration, 750-1000 ppm. You can scarify the seeds at first. Soak seeds for at 24 hours and at most three days for the ones enclosed in a hard coat. Keep the seeds at room temperature with occasional careful shaking. The seeds may then be sown. Donāt use it on easy to start seeds unless you dilute it greatly, like 25-100 ppm, and soak them only for 2-3 hours. Normal, easy-to-sprout seeds will become very elongated and stretched out, then die if GA3 is used on them. Concentrations of about 2 ppm can cause tubers to sprout earlier.
Gibberellic acid can also influence the timing of flowering, flower gender, flower size, and number of flowers. If a plant is sufficiently developed, premature flowering may be induced by direct application of GA3 to young plants. Formation of male flowers is generally promoted by concentrations of 10 to 200 ppm, female flowers by concentrations of 200 to 300 ppm. You may have an increase in the number of flowers by direct application of GA3 to young plants, at 25 ppm.
When there is difficulty with fruit set because of incomplete pollination, GA3 may be effectively used to increase fruit set. The resulting fruit may be partially or entirely seedless. GA3 applied near the terminal bud of trees may increase the rate of growth by stimulating more or less constant growth during the season. Since GA3 regulates growth, applications of very low concentrations can have a profound effect while too much will have the opposite effect.
Although GA3 is not listed as a poison, the following precautions should be observed. Flush with water any GA3 that may get into the eye. Avoid skin contact if possible and wash away any contact with soap and water. Avoid ingestion of GA3.
And, another random comment on using GA3 to reverse sex:
I breed autoās and feminized plants but donāt use colloidal silver. I use gibberilic acid which I find easier to work with. 2 grams per litre, twice a day until they have flowered and you have pollinated your females.
Not unusual to get several thousand seeds from a well grown female.
