Trying to change the PH in soil

14 years ago

Several pages back someone asked whether Ammonium Sulfate has the same effect as Alumminum Sulfate. I did not see a response. I'm curious if they do the same thing.

The post, at that time, had used apparently to much and the plant died.

For those trying to change Hydranga colors,I would recommend having soils analyzed before trying to change chemicals in ground. I had my garden bed soil analyzed at Texas A&M this winter. My phosphate levels were in the high range. My plants were showing signs of Chlorosis. I added both Aluminum Sulfate and Ammonium Sulfate to the bed in slightly lesser amounts than recommended & one month apart. I took mulched leaf and pine needle clipping and applied them in a 2" layer and worked them and the Sulfates into the bed. (about 4-5" down). I've had no problems and plants are looking better.

Not sure what color my Hydranageas will be. I'll let that be a surprise!

If anyone is interested in obtaining the article from A&M on Phosphorus you can call them. (979-845-4816) To clarify, they did not recommend the phosphates I did that on my own. I realize that this is going to take a couple of years to correct.

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gardengal48 (PNW Z8/9)
14 years ago
Yes and no :-) Ammonium sulfate and aluminum sulfate are two very different products. While both can help to lower soil pH, that is not their primary intent and one should be careful when applying either.

Ammonium sulfate is a high nitrogen fertilizer (21%N). It is often used in association with alkaline soils to reduce pH, but fast acting nitrogen can also encourage a lot of rapid, leafy growth at the expense of flowering. Over application can result in the 'burning' of plant tissue from salts and it has an ability to leach easily into groundwater, contributing to pollution.

Aluminum sulfate is sometimes sold as a soil acidifier and of course as 'hydrangea bluing'. It is the aluminum level in the soil that determines if a bigleaf hydrangea will bloom blue or pink. Freely available aluminum will result in blue flowers, unavailable aluminum will result in pinker flowers. And the soil pH will determine how much aluminum is available - acidic soils tend to have a higher available level of aluminum - in more neutral to alkaline soils, the aluminum is chemically bound and not freely available. Over applying aluminum is the issue - it is very easy to build up to toxic levels, even with hydrangeas. And many other acid loving plants - like rhododendrons and azaleas - are very sensitive to aluminum and you should avoid using aluminum sulfate in their vicinity.

It is the sulfate or sulfur in both products that have the acidifying effect. Just applying horticultural sulfur will successfully lower soil pH (to a degree) and without any harmful side effects. However, if there is not sufficient aluminum available in the soil, even acidic soils will not produce very blue hydrangea flowers. Other products that will help to acidify soils are cottonseed meal, and peat moss. And most organic mulches will buffer soil conditions to at least bring alkaline soils close to neutral. Chlorosis, or yellowing of the foliage, is very often a result of iron deficiency or lack of availability. This is very common with alkaline soils and chelated iron is an excellent amendment for correcting this problem.

Either of these products -- used in moderation -- can be helpful in adjusting soil pH and therefore influencing the flower color of hydrangeas, provided all other soil conditions are appropriate. It is always a good idea to have your soil tested to determine a) the existing soil pH and b) current nutrient levels, including all the trace elements.

It is also important to understand that it is extremely difficult to significantly alter soil pH one way or the other and that any adjustments tend to be quite temporary. If you have alkaline soils and/or irrigation water and want to grow very blue hydrangeas, it might make more sense to grow them in raised beds or containers where you can 'design' the soil to your requirements. Same with growing pink or red hydrangeas in very acidic soils.
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Trying to change the PH in soil

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gardengal48 (PNW Z8/9)

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