Develop intense blue hydrangea flowers by making the soil more acidic. Apply aluminum sulfate in October and again in March. Follow package directions.
Act now to keep chickweed from affecting your lawn in the spring.
Develop intense blue hydrangea flowers by making the soil more acidic. Apply aluminum sulfate in October and again in March. Follow package directions.
Garden columnist Dan Gill answers readers' questions each week. To send a question, email Gill at gnogardening@agcenter.lsu.edu.
I have a pink hydrangea and would like to know how to make it bloom blue flowers. — Andy Gordon
Hydrangeas are exceptional in that the color of their flowers can change depending on the availability of aluminum ions in the soil. Where aluminum ions are freely available for the hydrangeas roots to absorb, the flowers will tend to be blue. Where aluminum ions are tied up and unavailable, the flowers will tend toward pink.
Aluminum ions are most available in soils that are acidic and are less available in alkaline soils. South of Lake Pontchartrain, the soils are alkaline, and that tends to make hydrangeas on the south shore bloom pink or lavender pink. To encourage your hydrangeas to bloom blue, apply aluminum sulfate in October and again in March. Follow package directions. This makes the soil more acid and provides aluminum ions. Repeat this treatment every fall and spring until the plants bloom blue.
On the north shore, many of the soils are acid, and the hydrangeas bloom blue. If you would like to turn blue hydrangeas pink, apply lime instead of aluminum sulfate following the same schedule. This will make the soil more alkaline and tie up the aluminum ions. Remember, hydrangeas have already set their flower buds for next summer’s bloom and should not be pruned between now and then (although any remaining old, unattractive flower heads may be snipped off now).
My azaleas are dying. They are approximately 35 years old. I water them regularly, and they get good drainage. Since they started dying, I have been feeding them azalea food according to package direction, but it hasn’t helped. They started dying about one year ago, and until that time, they were always full, green and very healthy. They get partial sun. The leaves all turn brown, and the entire bush slowly dries up and dies. I have tried planting new azaleas to replace the dead ones, but the new ones die almost immediately. What can I do to get them healthy again? — Donna
Unfortunately, there is not much you can do for your planting of azaleas. Like all living things, plants get old and die. For azaleas, 35 years is a ripe old age. Your azaleas are losing vigor and weakening because of age, and that leaves them open to attack from fungal organisms that never bothered them before. This is not a problem with the growing conditions; they have been happy in their location and with the care you provide for them for decades. This is not a nutritional issue, and fertilizing will not help. This is an issue with the plants themselves.
What is probably actually causing the death of the azaleas are root rot organisms in the soil attacking and killing the roots. As sections of the root system are killed, the corresponding upper portion of the shrubs no longer gets the water it needs, withers, turns brown and dies. As the root damage progresses, the entire plant dies. These fungal organisms have always been present in the soil. It’s just that now that the azaleas are old, they are more vulnerable to attack.
You should be able to get new azaleas to grow in the area, however. When you have removed a dead azalea, thoroughly turn the soil in the area and incorporate a 2- to 4-inch layer of compost. The compost will encourage the growth of soil microorganisms that can help protect the new plants from root rot.
November would be an ideal time to plant new azaleas. Planted then, the cool weather will make it easy on the newly planted plants. And shrubs have a root-growth phase in the fall, so the new plants should begin to send new roots out into the surrounding soil right away. Regular rainfall over winter will minimize the care you need to provide.
In the spring, when they start to bloom and grow, fall-planted azaleas will already be well on the way to being established. However, the new azaleas will still need more frequent watering during dry periods next summer than the older, established plants.
Act now to keep chickweed from affecting your lawn in the spring.
STOP WEEDS: Apply preemergence herbicides to your lawn now to prevent cool-season annual weeds like chickweed, henbit, sticker weed and annual bluegrass from growing in your lawn. I’m often asked about controlling these weeds in the spring, when it is too late to control them most effectively. Look for products like Halts, Dimension, CrabX, Crabgrass Preventer and other brands, and follow label directions.
GARDEN FEST: The Fall Garden Festival at the New Orleans Botanical Garden takes place Oct. 8-9. It will include plant and garden product exhibits and sales, educational programs, music, arts and crafts, cooking demonstrations and more. The festival is open from 9 a.m. to 4 p.m. both days. Admission is $12 for adults, $6 for ages 5-12 and free for children 4 and under as well as Friends of City Park members.
AZALEA CARE: Azalea lace bugs feed from the underside of the leaves, causing small white dots on the upper side of the leaves and dark brown spots on the back. If you see these symptoms, spray two or three times under the leaves with permethrin, bifenthrin or a light horticultural oil following directions on the label. After treatment, the white dots will persist but not worsen.
Dan Gill is a retired consumer horticulture specialist with the LSU AgCenter. He hosts the “Garden Show” on WWL-AM Saturdays at 9 a.m. Email gardening questions to gnogardening@agcenter.lsu.edu.
October is a great time to plant cool-season vegetables into your garden. They include beet, broccoli, Brussels sprouts, cabbage, carrot, caul…
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