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Extension > Yard and Garden News > Selecting healthy plants

Monday, May 1, 2017

Selecting healthy plants

M. Grabowski, UMN Extension Educator


Salvia with the first stages of a leaf spot disease.
M. Grabowski, UMN Extension 
Starting out the growing season with healthy plants can be the key to a beautiful and productive garden. Plant pathogens can devastate a gardener’s dream of beautiful blooms or ripe red tomatoes. One key strategy in preventing plant disease problems is to purchase healthy transplants.

When visiting the garden center this spring, be a smart and selective consumer.

  • Read plant labels and choose plants that will thrive in the conditions of your garden. Think about the amount of sun the garden receives, soil type, and your ability to provide irrigation if Mother Nature does not.
  • Look for disease resistant varieties for common disease problems like powdery mildew or rust. 
  • Mix and match plants from different plant families. Many plant pathogens can only cause disease on one type of plant. Planting a diverse mix of plants reduces the pathogens ability to spread. 
  • Check how big the plant will get when fully grown. Space plants so that there is room for air flow between plants throughout the growing season. This will help leaves dry off quickly after rain and dew; which in turn will reduce problems with leaf spot disease. 


Inspect all plants prior to purchase. Reject any plants with symptoms that might indicate a plant disease problem.

  • Look at the inner and lower leaves where humidity tends to be highest.  Look for leaf spots, discoloration, or fungal spores. Be sure to examine both the upper and lower surface of the leaves.
  • Examine stems and branches. Stems of herbaceous plants like flowers and vegetables should be green and firm. Reject plants with sunken, soft, or discolored areas of the stem. Woody branches should be a uniform color and texture. Cracks, discolored bark, and oozing of sap are symptoms of infection. 
  • Pull the plant out of the pot and look at the roots. A healthy plant will have firm white to cream colored roots with many fibrous root hairs. Transplants with few roots, gray to brown soft sunken areas on roots, or that are lacking fibrous root hairs are suffering from root rot disease. 
  • Don’t buy plants from a group where some plants appear to have a disease problem. In a nursery setting, plants are tightly spaced and share many cultural practices like watering, fertilizing, and pruning. As a result it is easy for a pathogen to spread from one pot to another. If many plants in a group have a disease, it is likely that the few healthy looking plants are also infected but are not yet showing symptoms. 
  • Poor growth in this flat of vinca transplants indicates a problem.
    M. Grabowski, UMN Extension 
  • Don’t try to ‘save’ a sick plant. Plant pathogens can be brought into a garden on infected transplants and spread to other plants in the garden.  Many plant pathogens, once introduced, can persist in garden soil and plant debris, causing disease for years to come.  


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