University of Vermont Extension 
Department of Plant and Soil Science

Spring News Article


Dr. Leonard Perry, Extension Professor
University of Vermont

Three questions you may ask this month include why your seedlings are rotting at the soil line, how to get rid of crabgrass, and which shrubs should be pruned in spring.

Seedlings rotting at the soil line, then toppling over, is likely damping-off disease.  It often develops when seeds are sown in a seed mixture that is not free of disease (for example garden soil or used potting mix).  Overwatering helps the disease develop quickly.  If you broadcast seeds in a flat, and this disease begins, it can spread rapidly and kill most of the plants in the flat.

Do the opposite of conditions favoring disease, and you can likely prevent it without any chemicals.  Sowing seeds in rows will restrict the disease to a row if it develops.  Keeping the soil surface slightly dry, or sprinkling sand on it, can help control this disease.  Start with a pasteurized soilless sowing medium such as one you might purchase just for this purpose.

Dr. Lois Berg Stack from the University of Maine divides flowering shrubs into two major groups-- those that flower in spring, and those that flower in early to late summer.  Knowing the difference, you'll know when to prune.

Spring-flowering shrubs are said to flower on "old wood", because their flower buds develop in late summer but don't open until the following spring.  Allow these plants to flower before you prune them.  They include such plants as forsythia, white-
flowering spireas, mockorange, lilac, and most viburnums.

Summer-flowering shrubs produce flower buds each year as their branches develop, so are said to flower on "new wood."  These shrubs can be pruned in early spring, before these branches develop.  They include such plants as potentilla, hydrangea, and many roses.

Crabgrass is the bane of many gardeners, either in gardens or lawns.  It is a summer annual weed, which means that it grows from seeds as the soil temperature rises in spring.  The plants grow, set more seed to infest your garden, then die with frost.
Knowing this life cycle, you might figure that by preventing such annual weeds from going to seed you will help control future problems.  There are herbicides you might use containing "preemergent" chemicals.  This means they control the weed before it germinates and emerges.  Margaret Hagen, from the University of New Hampshire, recommends applying these to lawns when forsythia is in full bloom and, if it doesn't rain within a week, to water in.

To protect yourself and the environment, make sure to use any herbicides according to label directions, and only if needed.  A least toxic product you might look for is one containing corn gluten.  This natural plant product inhibits crabgrass and some broadleaf weeds, including dandelion.

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