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June 2015
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Mid-season tasks for more flowers and veggies

Annabelle and White Dome hydrangeas, blue larkspur and the seed heads of allium form a July Fourth bouquet of flowers cut fresh from the garden. © Jo Ellen Meyers Sharp

Annabelle and White Dome hydrangeas, blue larkspur and the painted seed heads of allium form a July Fourth bouquet of flowers cut fresh from the garden. © Jo Ellen Meyers Sharp

Even though the season of summer just arrived last weekend, the growing season has been upon us for three months.

And with all of the rain the last several days, plants have been on steroids, seeming to be ahead of their usual performance.

Weeds, in particular, seem to be thriving in my yard, and with the heat and humidity, the task of getting them under control is not pleasant. Hostas, too, seem to have emerged bigger and more lush this year. Some of us think this may have more to do with the past winter rather than the current season.

Some plants, especially those in pots, have just rotted off because of the humidity and rain. My sweet alyssum has all but disappeared because of the heat and rain.

What to do:

  • Apply a water-soluble fertilizer to pots, window boxes and other containers. Fertilize vegetables, too. For this, I prefer a granular product. Read and follow the label directions.
  • Give annuals a haircut, especially if they’ve grown leggy. Cut back to tidy up and shape the plant. With the dose of fertilizer, the annuals will snap back in no time.
  • Deadhead perennials. Not only does this tidy up the plant, it encourages the development of more blooms from side shoots.
  • Try to keep weeds under control. Weeds rob desirable plants of the nutrients they need to thrive. Fortunately, weeds are easier to pull after a rain.
  • Monitor for fungus diseases on plants. Fungus causes mildew, fuzzy growth and spotted leaves, as well as root and stem rot. Once a fungus is on a plant, there’s not much to do. Most fungus is opportunistic, which means the right conditions have to be in place for it to occur. If you chose to use a fungicide, always read and follow the label directions. Fungicides, even organic ones, are deadly to bees.
  • Be on the look out for aphids and other bugs. With all the rain, aphids may come calling for their favorite meal –bursts of tender plant growth. Also earwigs and millipedes seem to be abundant this year.
  • If your pots can be viewed from all sides, rotate them periodically to ensure good light exposure for the plants.

Lastly, pick a bouquet of red, white and blue flowers for your Fourth of July celebration and enjoy the holiday.

Downy mildew attacks basil

Downy mildew has taken a toll on basil the last few years. One symptom is fuzzy spores on the undersides of leaves. Photo courtesy Purdue Plant and Pest Diagnostic Lab

Downy mildew has taken a toll on basil the last few years. One symptom: fuzzy spores on the undersides of leaves. Photo courtesy Purdue Plant and Pest Diagnostic Lab

Basil has taken a huge hit over the last few years from a downy mildew, which can quickly decimate a crop in the farmers’ fields, growers’ greenhouses and our gardens.

Downy mildew is the common name for this disease, even though the fungus that causes it may be different, depending on the plant. It gets the name from the symptoms, downy-like fuzz on the leaves.

On basil, the culprit is Peronospora balbahrii. Initially, the leaves turn yellow, and then black spots appear. That’s followed by fuzzy spores on the undersides of leaves. The problem starts at the base of the plant and moves up. The fungus is air borne or can be splashed on plants from infested soil. Plants and seeds can be infected, according to the University of Minnesota Extension, which got its first reports of the disease in 2012.

Here in Indiana, Purdue University has seen only a handful of samples since 2009. “A couple each year,” said Tom Creswell, director of Purdue’s Plant and Pest Diagnostic Lab.

“Most of our reports from the home garden have been from the home garden of Tom Creswell,” he joked. “It seems that if this is showing up extensively in the home garden, then either no one is paying attention or it comes on so late in the season that they’ve already made pesto, or they don’t know they can send samples to the lab for help.”

What can we do?

  • Remove any infested leaves. It’s all right to eat healthy leaves from infested plants.
  • Plant resistant varieties. Sweet basil (Ocimum basilicum) is the most susceptible, which includes Genovese, Nufar, Italian Large Leaf, Queenette, Superbo, Poppy Joe’s and others, according to Minnesota extension. Red Rubin and Red Leaf (O. basilicum purpurescens) and lemon basils (O. citriodorum) are considered moderately susceptible. Blue Spice, Spice, and Blue Spice F1 (O. americanum) are less susceptible.
  • Don’t plant basil in the same spot year after year. If you grow basil in a pot, dump the soil each year and scrub the pot with a solution of one part bleach and nine parts water. Use fresh potting mix each year.
  • Give plants plenty of air circulation.
  • Closely examine basil plants at garden centers to make sure they are symptom free.
  • Consider growing basil from seed. It’s easy and plants comes up quickly.

Lilac trees extend the fragrant season

Lilac tree flowers are as fragrant as their shrub cousins. (C) Jo Ellen Meyers Sharp

Lilac tree flowers are as fragrant as their shrub cousins. (C) Jo Ellen Meyers Sharp

At garden centers, on garden tours, over dinner and in emails, people are asking about a tree with fragrant white flowers.

It’s a Japanese lilac tree (Syringa reticulata), a gorgeous beauty that blooms later than lilac shrubs. The ornamental tree has a rounded to pyramid form and reaches 30 feet or more tall and 20 feet wide. It is considered one of the easiest lilacs to grow.

The 12-inch long, creamy white flowers bloom in June, attracting butterflies, hummingbirds, pollinating insects and human attention. Cardinals, chickadees and finches like the seeds. The tree tolerates clay soil, deer browsing and salt spray.

Japanese lilac tree does best in full sun but tolerates light shade, which may reduce blooms. It needs decent drainage and is considered a good urban tree. You’ll see it planted as a street tree in several Indianapolis neighborhoods, along the Indiana Central Canal, the city of Carmel and other communities. It also makes a lovely hedge, windbreak or seasonal screen.

Good air circulation is recommended, even though the tree is considered resistant to powdery mildew, the plague of many shrub lilacs. It also is resistant to scale and borers, other pests of lilacs. If the lilac tree needs to be pruned, do so within a month after it is done blooming.

There are a couple of cultivars, but ‘Ivory Silk’ is the most widely available. More compact, ‘Ivory Snow’ gets up to 25 feet tall and is a profuse bloomer, usually a little earlier than the straight species of Syringa reticulata.

The seed capsules dry and are abundant enough to provide a bit of fall interest. The smooth, attractive, reddish-brown bark resembles a cherry tree.

For more information about the lilac trees and shrubs, download Lilacs for Cold Climates, a very helpful, free publication by Laura Jull, a horticulture professor at the University of Wisconsin.

Trees and shrubs to consider for your landscape

Native Virginia bluebell form a carpet of blue beneath the yellow Japanese Kerria. (C) Jo Ellen Meyers Sharp

Native Virginia bluebell form a carpet of blue beneath the yellow Japanese Kerria. (C) Jo Ellen Meyers Sharp

If I could only have one perennial for certain situations, such as shade or sun…that’s what we talked about in last week’s column. This week, we’ll look at a few shrubs and trees.

First up is viburnum, a species that has a shrub for about any location. There are several native viburnums that are garden worthy, including arrowwood (V. dentatum) and the American cranberry bush (V. opulus var. americana), sometimes listed as V. trilobum).

But my favorite is burkwood viburnum (V. x burkwoodii), a large, semi-evergreen shrub with fragrant, pinkish-white, waxy flowers in April and respectable leaf color in fall. Although burkwood does best in full sun, mine has been in part sun for years and does just fine. It gets about 8 feet tall and 6 feet wide. The size and the fact that it holds onto its leaves well into winter, make it a good choice for a three-season screen. It is drought tolerant and attracts butterflies and birds. The latter likes the showy fruit, which is not messy.

For deep shade, consider a kerria, sometimes called Japanese yellow rose (K. japonica). My preference is the single flowering kerria, called ‘Simplex’, but there’s a double flowering yellow (‘Pleniflora’) and single white one, too (‘Alba’). In my yard, the kerria gets early morning sun and blooms the same time as my Virginia bluebells (Mertensia virginica) to make a beautiful spring scene.

Kerria does not do well in full sun, which bleaches out the flowers. Arched chartreuse branches brighten the winter landscape. At maturity, it will get 3-6 feet tall and wide, suckering a bit to develop a colony. The suckers can be removed to keep kerria the right size for your space. It tolerates clay soil, dry and wet sites and deer. The flowers are about the size of a quarter and it’s not uncommon for kerria to rebloom in late summer. ‘Golden Guinea’ is slightly smaller than the species.

For a shade tree, I select a thornless honey locust (Gleditsia triacanthos var. inermis) for lots of reasons. The native tree provides dappled shade, which allows grass to grow underneath. The small ferny leaves also blow away in fall, reducing raking duties. This tree can become a problem if the roots are cut or removed, which can promote the growth of sprouts. There are several honeylocust cultivars available. At maturity, the tree will be 30 to 70 feet tall and wide.