plant care - Knowledgebase Question

helena, al
Avatar for edwardgirar
Question by edwardgirar
January 29, 2006
This refers to cutting back plants. I have 2 royal cape plumbago's and they have turned brown, lost their folage and died back this winter. Have I lost them? Do I need to cut them back? What time of the year? Should I cover them in the winter?

We also have 4 hydrangia and I have the smae questions. Last year I cut them back and they never bloomed. Do I cut them back and how do I get the flowers to be blue?

I planed Ajuga last year under my Bradford Pears. The area un der the trees is shaded 85% of the day. They have dies back. Will they come back? What flowering plant would work under these trees. They sre in the frt of the house which faces west. We have tried numerous types of flowering plants and nothing will take hold.

Thank You

Answer from NGA
January 29, 2006

That plant is hardy to about 20 degrees, maybe a bit lower if mulched well. Cut them back to about 6 inches and keep a deep mulch around the plant's base. They may return when things warm up again in spring. The flowers on hydrangea are blue in more acidic conditions. The mechanism of color variation in hydrangeas is the presence or absence of aluminum in the blooms. When aluminum is present the blooms tend to be blue. When it is not, they tend toward pink. Soil pH affects bloom color by making soil aluminum more (low pH or acidic soil) or less (higher pH or basic soil) available. To change the bloom color from pink to blue, add ? cup of sulfur per 10 square feet, mix it into the soil surface and then water it in well. To change the soil the blooms from blue to pink, instead of sulfur, mix in 1 cup of lime per 10 square feet. This procedure can take months to a year to change the soil pH and thus the bloom color.

For a faster reaction when changing from pink to blue, dissolve 1 tablespoon of alum (aluminum sulfate) in a gallon of water and drench the soil around the plants thoroughly 3 times, 4 weeks apart in spring. To rapidly change from blue to pink substitute 1 tablespoon of hydrated lime for the alum. Always apply these solutions to the soil and not the blooms or foliage or damage may result.

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