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Showing posts from April, 2011

Witches' Brooms on Landscape Shrubs

Michelle Grabowski, University of Minnesota Extension

Photo 1: Witches' brooms on willow.
M. Grabowski UMN Extension.
As spring slowly unfolds in Minnesota this year, many gardeners are anxiously watching the buds on their favorite landscape shrubs open up for the season. Some shrubs have one to several clusters of thin weak twigs arising from one point on a larger branch. These unusual growths are known as witches' brooms and they can form at the tip of the branch or lower down the stem. Many different problems can result in a witches' broom. Mites, fungi, aphids, salt or other damage to buds can all result in a proliferation of small branches, where only one should have emerged.

Another less known and little understood pathogen causes witches' brooms in Minnesota landscapes. Phytoplasmas are single celled organisms in a group known as fastidious bacteria. These tiny pathogens were unknown to scientists prior to 1967. They are very difficult and often impossible to gr…

Spring Pruning Tips for Woody Landscape Plants

Kathy Zuzek, UMN Extension Educator, Horticulture

Photo 1:Rodent damage girdled these stems.
K. Zuzek, UMN Extension.

Many shrubs are planted in landscapes for their wonderful floral display. One of the few shrubs that have bloomed to date during this slow-to-arrive spring is forsythia. With masses of yellow flowers, forsythias are wonderful plants in the spring landscape. But cultivars with appropriate flower bud hardiness for use in Minnesota are large shrubs with rapid growth rates. Their ability to quickly produce large quantities of upright and arching stems that tangle together to produce an unkempt-looking plant turns them into aesthetic liabilities in the landscape after blooming. Consistent pruning is the solution. Enjoy the floral display but remember that if you have reason to prune your forsythia, pruning should happen immediately after bloom.

Like many of our shrubs that bloom in early spring, forsythias produce flower buds on previous years' stems. To enjoy ma…

What are your apples doing right now?

Karl Foord, UMN Extension Educator

What are your apples doing right now?
Apple trees have two kinds of buds; vegetative buds that only give rise to leaves and shoots, and mixed buds that give rise to flowers as well as shoots and leaves. The parts of the flower in their primordial state can be identified in the dormant mixed bud as seen in this cross section (Figure 1).

Figure 1.

Bud stages

Apple flower buds progress through a series of developmental stages. This begins with the Silver Tip stage where the bud has started to open but no green tissue is visible. The progression runs through to petal fall and the beginning stages of development of the apple fruit (Figures 2 - 10).

Figure 2 and 3.

Figure 4 and 5.

Figure 6 and 7.

Figure 8 and 9.

Figure 10.

Apple varieties can break bud at different times, and buds can be at different stages on the same tree. For example, the buds on my Haralson apple tree are almost all between ½ inch green and tight cluster. Only the leaves are v…

Calendar: May 1, 2011

Most flowering annuals are available as sturdy seedlings at garden center and nurseries, but many will grow just as well or even better when you seed them directly into the garden. Zinnias, cosmos, bachelor's buttons, California poppies and marigolds are good examples of annuals that grow rapidly from seed. But if you want annuals for containers, buy well developed transplants that will look good the minute you pot them up.

Early May is a good time to plant grass seed, but for good results you need to rough up the soil first. Unfortunately, this exposes crabgrass and other weed seeds that will sprout right along with your new grass. To stop most weed seeds, apply a specially formulated version of pre-emergence herbicide right after seeding. The label must state clearly that it's meant for newly seeded lawns, otherwise it will kill desired grass seeds, too.

Attract butterflies to your yard by planting many good nectar-producing flowers. Include coneflowers, Russian sage, Joe-…