Issue: December 9th, 1996

Change hydrangea "flower" color

My family gave me a potted hydrangea plant a couple of years ago. When I got it, it had beautiful blue flowers. Now the flowers are an ugly purple color. Why did it change? Can I do something to make the flowers blue again?

The "flowers" on your hydrangea are really modified leaves called bracts, just like the so-called flowers of poinsettias. However, the hydrangea bract color can be modified by the pH of the soil in which the plant is grown. Hydrangeas growing in acid soil will have blue flowers. Those grown in alkaline soil will have pink flowers. Most greenhouse potting soils contain high levels of peat moss which tend to be acid, so hydrangeas grown in them are blue. In New Mexico water tends to have high levels of dissolved minerals and an alkaline pH. As you have watered you hydrangea, you have been changing the pH of the potting soil and thus the color of the bracts.

To get your blue bracts back on your hydrangea, you need to adjust the soil pH downward (make it more acid). It would probably be best to repot the plant after removing some of the old soil. Use an acidifying fertilizer and soil acidifier when watering it. If you are able to adequately acidify the soil, you may choose to raise the pH by adding lime to the potting soil. This will cause the bracts to be pink. Don't overdo it. The purple color you described is the result of a neutral pH in between acid and alkaline.

When to start tomatoes indoors

When can I start my tomatoes inside so that they will be ready to plant outside in the spring? I want to have tomatoes really early next year.

The usual answer to that question is to start them six to eight weeks before you plan to plant them outside. If your expected planting date is late March, plant them from the first week of February through about the middle of the month.

If you have a bright location, a greenhouse, or a coldframe in which to grow the seedlings before transplanting and can let them get fairly large, you can start considerably earlier. If you plan to use covering or some other method to protect against late frosts in the spring, you can also start earlier. If you live in a colder part of the state, plant them later. If you live in a warmer area, start earlier.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!