How to add color to your spring landscape

If you're looking for a way to punch up your spring landscape by adding some eye-catching color, consider planting hardy Minnesota azaleas. These shrubs were developed by University of Minnesota plant breeders at the Minnesota Landscape Arboretum to take the worst Minnesota has to offer, and they do! The plants are hardy down to 40 degrees below zero; their flower buds can withstand temperatures as low as minus 30 or 35.

The first Minnesota-developed azaleas, called 'Northern Lights,' were grown from seeds. They are lovely and sweetly perfumed, but because of the genetic variability in seeds, their blossom color ranges from pale pink to vibrant, deep rose. When buying 'Northern Lights' shrubs, you can't be sure of the color until you actually see flower buds open.

Several years after 'Northern Lights' were introduced, propagation techniques had improved, making it possible to reproduce plants with desirable colors individually, from cuttings. Each cultivar was given a name with the word 'lights' in it, including 'White Lights,' 'Rosy Lights,' 'Lemon Lights,' 'Mandarin Lights,' 'Golden Lights,' and so on. When you choose one of the 'Lights' series with a specific name, you can be assured of its flower color, even when it's not in bloom.

One of the newest and most beautiful Minnesota azalea cultivars should be available at nurseries and garden centers next spring. Its called 'Tri-Lights,' because its rosy buds open to pink petals that are tinged with rose on the edges and blotched with gold on the top petal. 'Tri-Lights' will be followed by two replacement azaleas; 'Candy Lights,' a pink-flowering cultivar that's proven much easier to propagate than 'Pink Lights,' and 'Plum Lights,' a pinkish-lavender improved version of 'Orchid Lights.'

Site selection

When it comes to growing azaleas successfully, half the battle is finding a compatible site. In the Deep South, where azaleas reign supreme, they're grown in partial shade. Too much sun compromises the beauty and longevity of their blooms, warms their shallow roots and dries the soil rapidly.

In Minnesota, however, azaleas belong in full sun -- as long as you don't place them up against the south or west wall of your house, where reflected heat will harm them. Though they'll tolerate partial shade, they won't bloom as well and gorgeous spring flowers are the primary (some would say only) reason to grow azaleas here.

Sunlight is not the only factor when choosing a site for azaleas. Good soil drainage also is critical. Azaleas are sensitive to waterlogged, poorly drained soil. An ideal situation for them is one where rainfall and irrigation water drain freely, yet a place where the soil retains enough moisture to remain cool and slightly damp.

If your soil is heavy and claylike, planting on a slope can help. It's also important to add plenty of organic matter before you plant. Adding enough organic matter and topsoil helps raise the planting bed and improve drainage. Incorporating organic matter works for sandy soils, too, because it allows them to hold more moisture.

Acidic soil conditions

Azaleas thrive in acidic soil, but most of the soil in the Twin Cities and surrounding areas (with the exception of parts of Anoka County) is alkaline. To grow azaleas well here, it's usually necessary to amend the soil prior to planting. A soil pH (the amount of acidity or alkalinity) of 4.0 to 5.5 is ideal. If you send a sample to the university's Soil Testing Lab and specify that you want to grow azaleas, they'll respond with a plan for acidifying your soil. You can lower pH (acidity) in just a few weeks by incorporating iron sulfate into the area. If you're in no rush, though, you can lower the pH by adding sulfur to the site this year and plant your azaleas the following year. (Sulfur is slower-acting, but you don't need to add lo clay103052as much as you would using iron sulfate.) Either way, mix plenty of peat or composted oak leaves or pine needles into the soil, and test the soil again next spring to see if it needs further adjusting.

General care

Because azaleas have shallow, fibrous roots, they're vulnerable to drying and damage from fluctuating soil temperatures. Maintain a 2-to 3-inch layer of mulch around the plants to help retain moisture and keep the roots cool. Shredded cedar bark or chips, ground oak leaves or pine needles are good mulches because they help acidify the soil as they decompose. Even with mulch, expect to water azaleas regularly in hot, dry weather.

Mulching also will help you squelch annual weed seeds. If any do germinate near the azaleas, you can easily pull them out of mulched soil. With mulch in place, you won't be tempted to use a hoe near the plants, which can damage the shallow roots.

Fertilize once or twice each year in spring and early summer with a product meant specifically for azaleas or blueberries. Granular ammonium sulfate often is used, as are liquid fertilizers that may be watered directly into the soil. Avoid products containing aluminum sulfate, even though they may be suggested for acid-loving plants. Aluminum sulfate damages azalea (and blueberry) roots, compromising their ability to grow vigorously.

Nip off azalea flowers right after they've faded, but don't prune the plants any further. Hardy azaleas grow rather slowly, so in most cases it's best to just leave them alone rather than trying to shape them.

'Lights' azaleas will grow about 4 or 5 feet tall and almost as wide, though some older specimens at the Minnesota Landscape Arboretum have grown even larger. Although it might take several years for them to get to the size you want, it's well worth the wait. The bigger the plants, the more spectacular their spring display.

-- Deborah Brown is a horticulturist with the University of Minnesota Extension Service Yard and Garden Line. For help with garden, plant and insect questions, call the Extension service at 612-624-4771 in the Twin Cities metro area or 1-888-624-4771 outstate.