Question
Hello again!

Thank you again for all your help with the geraniums.  They are still opening and dying off one or two florets at a time, so I am going to wait til they're finished, repot them and see if that helps...

I am trying my hand at adding aluminum sulfate to my potted hydrangeas to maintain the blue, and I wonder if you have any experience in this area...  I have the formula down (1/4 oz sulfate per gallon of water), and am drenching the plant with plain water first to protect the roots and plan to start using a 25/5/30 fertilizer, but am wondering:

- Should I add the sulfate every time I water?
- How much should I add? (I have been drenching.)
- Do you know if this will only affect new blooms, or will the older ones that have faded change back also?

Am hoping I have the patience to do this right...  Thanks in advance for your usual expert advice!

Nancy in TX  

Answer
How nice to hear from you again Nancy,

As you know I am the Long Island Gardener - and although the north part of the Great State of Texas can be anywhere from 6a to 7b, gardening is so much more complicated than USDA zones.  I think you pretty well described that predicament.  A Texas 7b is worlds away from a Long Island 7b -- just the water alone is different, the soil is different, the weather...

Just keep that in mind when you read ANYTHING I tell you because the most important knowledge we have comes from experience.  The closest I have ever been to Texas was when I flew over it on my way to California 20 years ago.  I have ZERO experience growing ANYTHING in Texas, Nancy.

YOU on the other hand have made some mistakes -- which is absolutely the BEST education money can buy.  I can't emphasize that enough, Nancy.

So with that caveat now out of the way, I will do my best to give you my best advice on your Hydrangea.

We have to begin with the understanding that this is Hydrangea macrophylla you have -- correct?  The "Bigleafed Hydrangea" that made Cape Cod famous?.  

There are many others out there.  Growing those would have different instructions, so just so we are on the same page we're talking Macrophylla here.  This is not a shrub that is simply split into Pinks, Blues and Whites.

(As a gardener by the way Nancy I KNOW you know that.  I have to say it though because hundreds maybe thousands of people will be reading this and although they love those large-flowered H. Macrophyllas they may have something different.)

Now for a talk about those exceptional blues.

Blue is so hard to come by in the garden, and these are so generous with their blue flowers.  Easy plants, almost trouble free.

So Nancy, you have read the general advice about blue-ing up by acidifying the soil; the more acid, the brighter the blue.

But what you don't read often enough is that the Blue you'll get is a genetically preprogrammed color -- DNA-determined instructions for Hydrangea sepals to make anthocyanin and some other pigment.  You can reach "Blue" with a typical Hydrangea.  But if you have an older variety, which is the case at my house, there is ju  st so much Blue you can squeeze out.  There is a ceiling.  It does not budge.

Because so many people favor that elusive garden blue, newer Hydrangea hybrids have been bred for better Blues. If you are living at the beach in Cape Code with your greatgreatgrandmother's 200-year-old Hydrangea, it will NEVER be as blue as one you buy today at the local nursery.

You have acquired a Hydrangea that is currently potted.

Nancy, there is an art to Container Growing.  EVERYTHING becomes a balancing act.  ESPECIALLY fertilizing.

Shrubs purchased in Containers come with their own Growing Medium.  What's in there?  Who knows?  Pure or amended peat moss?  Any idea?  We'll come back to this later.

As far as watering, the best thing you can do -- and this goes for all growing plants, potted or grounded -- water with a dilute fertilizer (or vinegar) every single time.  It is always better to give small doses than to give less small doses once a week or bigger doses once a month.

Sorry to say, if your flowers are not blue enough for you, this is not a change you will notice overnight.  I have heard of people waiting a season or longer to see their favorite blue.  It is my understanding that the whole point of acidifying the soil is to make the aluminum available to the plant for blue pigment.  Aluminum is soluble at a soil pH of 4.0-5.0. Pink Hydrangeas absorb less aluminum; a pH 6.8-7.0 blocks absorption, and the flowers lose all blue.

Aluminum sulfate does both -- acidifying soil and feeding Aluminum.  If you have aluminum in the soil already, you don't need to add aluminum.  Overdosing is in the cards for you if you keep up with too much Aluminum sulfate.  Many people buy their Hydrangeas in pots; the growing medium almost always contains high amounts of peat moss, negligible if any Aluminum.  To grow blue Hydrangeas, these people MUST add Aluminum sulfate to provide the Hydrangea with Aluminum.  Probably because Aluminum is used for pigmenting, Hydrangeas have a special tolerance for it.  But you can overdose with Aluminum if you are not careful.

If you were growing these in the ground, you would have to worry about the other plants around the Hydrangea. Aluminum Sulfate is a poison.   To understand this better, imagine going back to your High School Chemistry class and getting a bottle of Sulfuric Acid, then diluting it and putting it on your Hydrangea.  

Aluminum Sulfate is a layman's expression for... Sulfuric Acid.

Surprised?

So remember that.  Not only when using it in the garden, but when you mix it yourself.  And by the way, simply breathing the dust is bad for YOU.  Hold your breath.

Now, about that 25-5-30 fertilizer you are going to use...

Normally, I would tell someone who wants to grow a flowering plant that you are under-doing the Phosphorous.  A 25-5-30 label tells you the stuff inside is 25% Nitrogent and 30% Potash, with only 5% Phosphorous.  Big Phosphorous numbers create Big Blooms.  So you want a high-Phosphorous fertilizer, right?

Not so fast.

At "L'Atelier Vert" website, the Hydrangea-loving editor posts a page that will tell you everything you've ever wanted to know about Hydrangeas but were afraid to ask in her Everything French Gardening (www.frenchgardening.com/aujardin.tmpl?SKU=3108978205110023) column.  And the author explains that the problem with this high-Phosphorous philosophy is that Phosphorous "will displace the aluminum, making it less available to your Hydrangeas."

For organic gardeners, they recommend aged cow manure -- "the only manure that is mildly acidic."

Getting aluminum into the ground is not so easy. In France, powdered slate (from old French roof shingles) is used. (I am working on sourcing this product in order to be able to offer it on this site.) It contains a slow-release, organic form of aluminum sulfate. That's why Hydrangeas planted next to slate-roofed houses are always a brilliant blue; the rainwater runoff from the slate supplies plenty of aluminum in just the right, gentle doses."

Ammonium sulfate contains about 20 percent nitrogen.  Miracid:  30-10-10
Miracle-Gro Quick Start Transplant Fertilizer: 4-12-4.
Miracle-Gro Indoor Plant Food Spikes: 6-12-6
Miracle-Gro Shake n Feed for ContainersL 19-6-12
Miracle-Gro Water Soluble Flower Food: 15-30-15

Also, Aluminum Sulfate has a VERY high salt index.  When you use it all the time, salts build up, damage the roots, and make your Hydrangea sick.

This is the balancing act that we mentioned earlier.  Note that florist Hydrangeas almost always are heavily dosed with Aluminum Sulfate.  To keep your Hydrangea happy, you have to make sure you water this shrub in the pot VERY heavily -- enough to saturate and flush built-up salts...

...and yet, you cannot let the pot dry out.    

How can you avoid this?

Fertilize occasionally with Aluminum Sulfate.  In between, use a Vinegar + Water solution.  You can also toss unfinished glasses of Orange Juice and ready-to-expire Apple Juice and Apple Cider on your Hydrangea.  If that's too messy, try a top dressing of peat moss mixed with coffee grounds which as I may have noted already once Starbucks is giving out for FREE this Summer, special bags and all.  F - R - E - E free!

As for the Texas experiment, I have heard that although Hydrangeas are very hardy shrubs, their buds are NOT so tough.  In some regions, they need protection just like Roses and other plants.  Your North Texas climate is SO  unfamiliar to me. I don't know what to expect.  But I'm willing to learn!  

Here's to More Better Blues.