Wednesday, February 29, 2012

Growing Healthy Plants, part I: Sanitation is Not a Dirty Word

With spring nearly upon us, gardeners are dreaming of yards overflowing with healthy flowers, vegetables, and greenery of all kinds. Before you dig your gardening tools out of the shed and start planting, here are some tips for growing happy, healthy plants!
Sanitation is a key to growing healthy, disease-free plants. If you are growing plants in pots, baskets, or raised containers, start with sterile potting media. Old potting media can be full of pathogens ready to attack new plants. Pathogens like Pythium or Phytophthora can survive in soil for years. Using sterile pots goes hand in hand with using sterile soil. Scrub used pots with a stiff brush to remove all soil and organic debris. After a thorough cleaning, sterilize pots by soaking for at least 30 minutes in a solution of 1 part bleach to 9 parts water (about 12 ounces of bleach per gallon).

Dirty equipment is a common means of spreading pathogens to healthy plants. Remember to scrub garden tools and soak them in a bleach solution at the start of the season and after using them to cut or dig around diseased plants. Rinse metal tools after the bleach treatment to avoid corrosion. Alcohol can be used to disinfect cutting tools and is less corrosive than bleach.

Now that you have clean pots, tools, and media, it’s time to pick your plants. Always buy healthy plants from a reliable source: pathogens can enter the garden on diseased plants. A well-run nursery should be very clean, with few weeds, algae, or loose soil on the ground or benches. Nurseries with neat, well-organized displays, minimal crowding, and plants that are neither to wet nor too dry probably use good practices overall and are likely to sell only the healthiest plants. Cull piles and dumpsters should be far away from the sales and production areas. Mimic these practices if you are propagating your own plants.  
Good Practices: Notice the clean benches (Photo: B. Shew)
Poor Practice: Algae, Standing Water, Organic Debris (Photo: E. Lookabaugh)
Poor Practice: Cull pile next to healthy plants (Photo: E. Lookabaugh)
Be sure to inspect all plants before you buy or transplant them. Do not buy or move plants that are wilted, yellowed, stunted, or have any other symptoms or unusual appearance. Inspect the roots of potted plants or transplants. Look for containers or plugs thoroughly colonized (but not pot-bound) with healthy roots. Healthy roots can be brown or white, depending on the species, but they should never have obvious rot or lesions. The potting medium or soil should have a pleasant, earthy odor. Avoid plants growing in stagnant-smelling medium.
Nice White Roots (Photo: E. Lookabaugh)
Be very cautious when dividing or transplanting plants in your yard and be very, very careful with plants from neighbors or plant exchanges. Before putting these plants back into the landscape, brush or wash away excess soil, remove dried leaves, and prune away any dead stems in woody plants. Carefully inspect all parts of the plant for symptoms and do not use any plant that appears to be diseased. If at all possible, pot transplants or divisions in a location well away from your landscape. Watch transplants carefully while they are in your quarantine area and move them to their final destinations only when you are confident that they are disease-free.

In the landscape, rake up old mulch, fallen leaves and other debris before planting and LIGHTLY cover the area with a new layer of mulch after planting. Once you are done planting, be sure to monitor plants closely. Promptly remove all fallen leaves, spent flowers, unwanted produce, and dead or cankered stems. In many cases, composting cannot be counted on to kill pathogens, so promptly destroy any materials you removed from diseased plants or their surroundings.
Remove fallen, diseased flowers to prevent inoculum splashing up (Photo: B. Shew)
If you start seeing disease symptoms, contact your local county agent or the Plant Disease and Insect Clinic. Sometimes, our diagnosticians can diagnosis plant disorders from digital images. Take a photo and email it to us. We will be able to advise you as to whether you should remove the plant, or if sending a physical sample is necessary to diagnose the problem.
Sometimes gardening is best done with a buddy!
For more information on sample submission see our webpage: