Hydrangeas change colors due to soil


Hydrangeas that grow in more acidic soil will bloom into a blue flower, while less acidic soil will produce a pink flower.

Special to The Sun
Published: Saturday, July 1, 2006 at 6:01 a.m.
Last Modified: Saturday, July 1, 2006 at 12:00 a.m.

Q:

I know that the pH of the soil makes the flowers of the hydrangeas either pink or blue. Does acid soil make pink flowers or blue flowers? Can you change the colors?

A:

It is the acidity of the soil that determines the different colors of the big leaf hydrangea (Hydrangea macrophylla), but the mechanism of the color variation is from the presence or absence of aluminum in the flowers. The pH of the soil affects the amount of aluminum that is available to the plant.
If the soil is acidic, less than pH 7, then aluminum is available to the plant, and the flowers are blue. So to answer your question, acid soil equals blue flowers.
Blue hydrangeas are beautiful, and the pink blooms are lovely too, but if the flowers are always prettier on the other side of the fence, you might choose to fool with Mother Nature. If you want to change the color of your blooms, it is possible by adjusting the soil pH.
To change from pink to blue, you will need to create a more acidic soil. Do this by broadcasting 1/2 cup wettable sulfur per 10 square feet and water it in. This method will take about a season before you see the results.
For a more rapid change from pink to blue or to make your flowers even more blue, simply add one tablespoon of aluminum sulfate or alum in a gallon of water and drench the soil around the plant.
If you would prefer to change from blue to pink, you need to make the soil more alkaline. Do this by adding hydrated lime. Dissolve one tablespoon of hydrated lime in a gallon of water and pour it around the soil of the plant once in March, April and May. Be sure not to get any of the lime solution of the plant leaves or yourself, because it will burn.
Hydrangeas bloom on old wood, so remember to prune them soon after they have bloomed. For fresh information on hydrangeas, check out a UF/IFAS document on New Hydrangeas for North and Central Florida.
Access it at http://edis.ifas.ufl.edu/EP287 or call the UF/IFAS Alachua County Extension office at (352) 955-2402 and ask for one to be sent to you.

Q:

Last year, I planted gladiola bulbs, and they bloomed beautifully. This spring they came up and had flower stalks on them, but they never bloom completely. I'm watering regularly, and other perennials in the bed are doing OK.

A:

This spring was very dry, and the fact that your gladiolas set buds and didn't finish blooming makes me think that they were not getting enough moisture.
I understand that the other plants in the bed are performing well, but in our sandy soils and with the glad's lush growth, they can require more water than the rest. Also, over-fertilization can interfere with blooming. Try to use a slow release fertilizer around them.
My suggestions for next year's blooms are to make sure they are getting plenty of sun and work in some organic matter around the plants.
Then water regularly. Adding compost or composted manure will increase the water holding capacity of the soil. Your normal irrigation water will be held on to longer. Work in the compost, so you don't bury the corms too deeply. The corms should be 4-6 inches deep.

Q:

My tomatoes are dropping blooms. As a result, I am not seeing any tomatoes. I have planted them in an earth box on my patio by the pool. They get good amount of sun.

A:

Some folks make growing tomatoes look easy, and the rest of us just sort of struggle along. There are a few reasons why tomatoes drop flowers, one of which is dry soil.
Since you are using the earth box, which provides constant soil moisture, I know that lack of water is not a concern. Tomato plants really require a good deal of bright sunlight. Upwards of eight hours a day or more would be ideal, so if your plants are not getting intense sun, you will not get fruit.
But I am pretty sure the real culprit here is our daytime temperatures. Tomato fruit will not set when daytime temps are above 90 degrees for hours a day. You will see plenty of flowers, but no fruit. It is simply too hot.
This is a good reason to get your tomatoes planted in the first couple of weeks of March. Early planting means you can set fruit when days are in the 80s, and harvest in May and into June.
There is another way to get tomatoes during the hot months of June and July. Use heat tolerant tomato varieties that can set fruit in hot temperatures. Try varieties like 'Solar Set' and 'Solar Fire,' both of which were bred at the University of Florida.
Wendy Wilber is the UF/IFAS Alachua County Environmental Horticulture Extension Agent. If you have landscape or gardening questions you can contact her or the Master Gardener desk at 955 2402, or send questions and digital images to alachua@ifas.ufl.edu.

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