Soil conditions may aid clover

Dear Carol: Do you know of a solution for clover that has invaded a bed of sweet woodruff? We have pulled it out by hand only to see it come back more than before, and it is taking over. Is there a weed killer that could be applied that would not harm the sweet woodruff? -- K.K., via e-mail.

 Dear K.K.: Unfortunately, weed killers can't tell the difference between clover and sweet woodruff, so a chemical that would kill the one would kill both. However, sweet woodruff is a vigorous plant. Usually people write me to complain that the sweet woodruff is taking over. If it's being outcompeted by clover, that suggests the conditions aren't optimal for sweet woodruff.
 Clover and related plants are legumes that can get nitrogen from the air by associating with nitrogen-fixing bacteria in the soil. If the soil is low in nitrogen, the clover would have an advantage over the sweet woodruff. It might be that fertilizing in early spring could help the sweet woodruff grow better.
 Sweet woodruff is a low groundcover for shade with tiny, starry white flowers in spring. The flowers aren't fragrant, but the dried foliage is vanilla scented. It is used to flavor traditional German May wine, liqueurs and sachets.

 Dear Carol: In your article in The Post-Standard on Sept. 4, you talked about adding aluminum sulfate to soil around hydrangeas to make the blossom turn blue. Is there any treatment in the fall for hydrangeas that you want to stay pink? -- R.S., Manlius.

 Dear R.S.: If the hydrangeas are naturally a good, clear pink without any soil amendments, then they will stay that way. If the hydrangeas are pinkish-purplish-bluish and you would like them to go one way or the other, aluminum sulfate solution (2.4 ounces per gallon of water) can be watered into the soil two times two weeks apart in September to make the flowers blue.

 Lime makes the flowers pink. A soil that is formed from limestone, as many soils around here are, will be alkaline so the hydrangeas will be pink. Dolomitic limestone added to the soil around the plants will change the color, but lime is very slow acting and it will take repeated applications and several years to see results.

 The only hydrangeas to which this applies are the pink or blue bigleaf hydrangeas. White hydrangeas won't become blue or pink no matter how much aluminum sulfate or lime you add. Many white hydrangeas do take on a pink color as they age, though.

 Another reader asked about peony colors. These flowers are unaffected by the acidity or alkalinity of the soil. If you choose a pink-flowered peony variety, it will stay pink. There are no blue peonies.
