Start the season right with healthy plants

Learn what to look for while you shop!

M.Grabowski, UMN Extension 

Coleus for sale at a local garden center
Photo: M. Grabowski, UMN Extension

The first step to prevent disease problems in the garden is to start out with healthy disease free plants.

Many plant pathogens are able to hitch a ride from one garden to the next by infecting plants before they are sold or shared. This can result in disease problems for years to come as the new pathogen becomes established along with the new plant.


In the worst case scenario invasive pathogens are brought in from outside of Minnesota and escape the garden to cause disease in Minnesota native plants. White pine blister rust, a devastating invasive disease of white pines, was first brought into the USA on infected pine seedlings.

Whether you are looking for tomato transplants, annuals or perennial flowering plants, or a new tree or shrub, take the time to follow the simple recommendations below to purchase healthy plants.

Inspect every plant prior to purchase

Dark wilted stems indicate this periwinkle is infected with a plant pathogen.
Photo: M. Grabowski, UMN Extension

At the nursery or garden center, carefully inspect every plant prior to purchase.

• Look at the upper and lower leaf surfaces for spots, discoloration, unusual growth or other signs of disease.
• Examine the stem. Are there any open wounds, excessive sap, discolored or soft mushy areas? These could all indicate a disease problem.
• Examine the roots. They should be firm and light colored with many fibrous root hairs. Dark mushy areas may be infected with a root rotting pathogen.

 Implement a strict ‘no pests allowed’ policy

• Choose only healthy looking, vigorously growing plants for your garden.
• Reject any plants showing symptoms of disease.
• Never try to save a sad looking, weak plant. The proper place for these plants is in a compost pile that heats up enough to kill any pathogens.

Reject plants with sick neighbors

Snap dragon transplants with root rot.
Photo: M. Grabowski, UMN Extension

Nursery plants are often grown close together, grouped by plant type or variety. The plants within a group are all pruned, watered and fertilized at the same time. If one plant in a group is diseased, it is easy for the plant pathogen to move from one plant to another during these maintenance practices.  If several plants in a group appear diseased, do not purchase any of the plants within the group.

Choose plants suited to your site

Read plant labels to look for disease-resistant varieties and
to find out if the plant will thrive in the conditions in your garden.
Photo: M. Grabowski, UMN Extension

Read the plant tag carefully. Is this plant hardy in your area? Will the plant thrive in the conditions of your garden? Plants stressed by cold, drought, too much sun or shade or other environmental problems often suffer from disease problems in addition to environmental stress.

Look for disease resistant varieties

Whenever possible purchase plants that are bred to be disease resistant. Many common disease problems like apple scab on crab apple, powdery mildew on phlox and Verticillium wilt on tomato can be avoided altogether by growing disease resistant varieties. Disease resistance is often listed on the plant label.

Certified disease free plants

Rose Mosaic Virus
Photo: M. Grabowski, UMN Extension

Some plants like roses and hostas are screened by some nurseries to verify that they are free of viruses like Rose Mosaic Virus and Hosta Virus X. Ask at the nursery if these plants have been screened or ‘indexed’ for virus prior to purchase.

What about dividing and sharing plants?

Splitting and sharing perennial plants is a tradition as old as gardening itself and can be a cost effective way to grow your garden while connecting to friends in the gardening community. If you are receiving plants from a split perennial, accept plants from someone you know and trust. Volunteer to help dig and split plants. This will allow you to see the mother plant.

Select vigorously growing plants for division. Examine the plant carefully for any signs or symptoms of disease. Look for spots, discoloration, unusual growth, or rot on all plant parts. Reject plants that have symptoms of a disease. Healthy looking, vigorously growing plants can be split and shared.

Gardeners may choose to take extra precautions by isolating the new plant in an area away from the main garden bed for a year to watch for potential problems. This way, if a disease problem does come up, the plant is easily removed and it is less likely to spread to your other well established perennials.

Never share plants from gardens outside of Minnesota! Invasive pests that threaten our native plants may be hiding on these transplants!