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July 26th, 2012

How to Change Your Hydrangea’s Color

The hydrangea that was a gorgeous shade of blue when I bought it last year bloomed pink this year. How can I get it back to blue?

blog-dougThe flower color of certain types of hydrangeas depends on the amount of aluminum they draw from the soil, which in turn depends on soil pH. In general, they bloom pink when soils are alkaline or neutral, or toward the blue/violet end of the spectrum when soils are acidic.

Many of the beloved mophead and lacecap varieties of Hydrangea macrophylla respond to changes in soil pH by shifting their flower color. Gardeners have learned to manipulate the soil to take advantage. It’s too late to change the color of your hydrangea this summer, but here’s how to alter it by next summer:

To obtain blue flowers, increase soil acidity by adding sulfur, with your goal being pH 5.5 or lower. Sprinkle about ¼ cup (if the soil is sandy) or ½ cup (for clay or loamy soil) of garden sulfur at the base of the hydrangea and water it in.

For pink flowers, use dolomitic lime to decrease acidity; aim for pH 6.5 or higher. Start with about a pound of lime, scattered around the root zone of the shrub and scratched into the surface. Use half that amount if your soil is sandy.

It’s not an exact science. Some soils (and some hydrangea cultivars) are stubbornly resistant to change. You may need to repeat the application, and even then you may never get the color you want. And don’t expect immediate results; lime or sulfur applied in fall will affect the following summer’s blossoms. Some soils can maintain the color shift for several growing seasons while others will revert after a year.

I used to live in Kansas City, where naturally limey soils tend to keep hydrangeas pink, and gardeners go out of their way to achieve blueness. Now I’m in Pennsylvania, where blue hydrangeas are commonplace and discerning gardeners strive for pink. To my eye, they’re all beautiful.  —Doug Hall

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July 17th, 2012

Embrace Your Brown Lawn

With all the hot weather we’re having in Iowa, my bluegrass lawn looks kinda brown. Would a summer feeding help it to green up?

blog-dougWhen a lawn is stressed from heat, fertilizer is the last thing it needs. Cool-season turf grasses, including bluegrass, fescues, and perennial rye, slow their growth in response to hot weather. If the weather is dry as well as hot, you’ll notice a lot of brown blades among the green. This summer “dormancy” can last through Labor Day or until cooler weather and fall rains prompt a return to green.

You could keep the lawn green through summer with copious amounts of water. But I would argue against that sort of wastefulness. Instead, why not take a break from mowing and allow the lawn to go dormant?

There’s one caveat to letting the lawn brown out, and that is the chance that patches of turf will die if the weather stays dry for too long. A good soak every 2 or 3 weeks is all it takes to keep bluegrass alive. Depending on your soil type and how dry the soil is to begin with, it could take between one-half inch and one inch of water to soak the ground to a depth of 6 inches. If natural rainfall fails to provide this much, you’ll have to step in. Apply water in the early morning, when less will be lost to evaporation, and water slowly so every drop sinks in.

Other summer strategies for keeping a lawn healthy include setting the mower blade high—up to 4 inches—and using a mulching blade that drops finely chopped clippings back on the lawn.

Save the fertilizer for fall. Bluegrass and other cool-season grasses naturally regenerate in fall, when temperatures drop and soil moisture is more abundant. In fall, bluegrass will devote the extra nutrients to extending and thickening its root system instead of producing more top growth. Choose a slow-release organic product.  —Doug Hall

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July 6th, 2012

Growing Foxgloves From Seeds

How do I grow foxgloves from seed? I admired my neighbor’s foxgloves this spring and she offered me seeds.

blog-dougI’m a fan of foxgloves of all types but especially Digitalis purpurea, the common biennial foxglove. They’re easy to grow from seed; one packet yields a generous drift of plants, which is fortunate, because the tall, tapering spires tend to look best when there are lots of them.

Gather seeds from your neighbor’s foxgloves a few weeks after they finish blooming. Stalks that were not deadheaded after flowering will have turned brown, bearing a gazillion seeds each. The seeds shower out of the seed capsules in abundance as you clip the stalks. It doesn’t take long to fill an envelope with seeds, even though they’re tiny.

The only trick to growing foxgloves is the timing. They’re biennials, which means they produce a rosette of leaves in their first year and a vertical spike of flowers the following spring. Sow seeds now, in early July. Some gardeners grow the seedlings in a flat and transplant, but I’ve always found it easiest to sow them in the garden where I want them to bloom next year or in a partly shaded “nursery” bed. Dig the soil to loosen the surface, mix in some compost, and then sprinkle the seeds over the ground. Keep the bed moist while the seeds are germinating.

Eventually—sometime in September or when the seedlings are about 4 inches tall—you’ll need to thin the seedlings so they’re spaced about a foot apart in all directions. It’s tempting to leave more, but crowded seedlings tend to produce wimpy flower stalks. Fortunately, they are easy to transplant at this stage, so you can share the extras with your neighbors. The plants will go dormant when winter arrives, only to return for their grand show next May.  —Doug Hall

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