Monday, March 5, 2012

Why Sanitize? Spring Cleaning Your Containers.

By Jessica S Herwick
Re-using your pots from last year can be a big money saver, and it reduces waste, which is always a plus. Even so, thrifty gardeners should beware!  You could be recycling all sorts of problematic pathogens, damaging mineral/salt deposits or even last year’s weeds in an effort to reduce your carbon footprint. 

The difficult to prevent white and gray rings that develop around your containers are mineral and salt deposits that accumulate over time. These are unattractive to some gardeners but can actually dehydrate a plant if the roots sit against areas with extreme collections of these deposits.  Spores and bacteria that cause mold, fungus and even root rot can stick to your containers, but hide from the naked eye.  This makes it impossible to detect which pots are harboring trouble for your new plants. So, even if it looks clean, it may not be.  Many of these pathogens will remain undetected until your seedlings are growing strong and then - BAM! - Out of nowhere, problematic and often fatal plant illnesses begin to crop up unexpectedly.

To diminish the risk of transferring mold, viruses and harmful bacteria from one seedling to the next, plan to sanitize your recycled pots, flats and gardening tools as you plan for this year’s garden.  Try the following methods for easy, affordable sanitization of your pots, flats and gardening equipment or see the links to read more about sanitization methods.  While you’re at it, consider pasteurizing your old potting soil instead of purchasing new bags this season.


You Will Need:  
Chlorine Bleach
(Also known as household bleach. Use only unscented.)
Liquid Measurement Device
(You can use most anything: measuring cups to reused gallon milk jugs. It just depends on the amount of solution you need to mix.)
Rubber Gloves or Kitchen Gloves

STRENGTH OF SOLUTION:  You want to mix a bleach and water solution that is strong enough to kill the harmful debris and break down remains from last year’s plants that might stick to the edges of the pots.  At the same time, if the bleach solution is too strong, it will be difficult to rinse from the pots – especially clay, terra cotta or other containers made of similarly porous material.  You do not want the bleach to come into direct contact with the new plants that you’ll eventually place into reused containers, so measure carefully, and the rest of the process will be a piece of cake.

SOLUTION RATIO:  The rule of thumb ratio, and the recommendation from the Penn State Extension Office is a 1:9 solution, meaning 1/10 unscented, chlorine bleach to 9/10 water.  The amount of solution you will need to mix will depend on the size and shape of the containers or equipment you are sanitizing.  You need enough space to completely submerge your containers (or all pieces of metal for gardening tools) in a pool of the bleach solution. Test out a large sink, bucket or basin to ensure your materials will fit well; Base your ratio on the amount of liquid your basin will hold. Estimating is okay, but try to stay as close to the real math as possible.

CONVERTING: One gallon equals 16 cups; One tenth of that is 378.541178 milliliters, or 1.6 cups. For a gallon container you would mix 1½ cups bleach with 14½ cups water to total 16 cups of liquid solution – or one gallon. Simple math can help you determine the proper ratio, or you can try an online conversion site and let them do the math for you! The conversion sites I have found to be the easiest and most helpful are listed below.

Hint #1:   Mix the bleach solution in a standard five-gallon bucket, then transfer the solution into spray bottles, or back into empty bleach containers for later use.  The fresher the solution, the stronger it will be.  Solution will keep well over time, but looses its strength the longer it sits.  If you cannot smell the bleach/chlorine in the water when you take a small sniff – if it doesn’t sting your nose at all - then the solution is no longer potent.  Use this method to test old bottles of solution before using to ensure success.
Hint #2:  Recycle your clear plastic, gallon milk jugs for easy measuring and storing!  Set a few aside before you put your weekly recycling out on the curb.  I mark off the line where 1½ cups of bleach sit on the outside of the milk jug with a sharpie.  Then, when it’s time to mix, I fill the bleach to my pre-marked line (using a funnel) and fill the rest of the jug with lukewarm water.  If I’m filling a five- gallon bucket, I do this 5 times, pouring the mixture in one gallon at a time.  This also helps to mix everything up, eliminating the need to stir the solution.

ALTERNATIVE METHOD: If you are absolutely against using chlorine bleach, you might want to try using heat to sanitize in place of the bleach solution. After using dish soap and warm water solution to scrub debris from your pots or garden tools, submerge and soak in boiling water  (180 degrees Fahrenheit at all times) for 30 to 60 minutes. The longer you maintain the temperature and continue the soak, the more pathogens you are killing off. Upon removing items from the hot water soak: Wash gently with mild soapy water (using dish soap again).  Rinse until the water runs clear, and set in direct sun to dry for 12 hours. May Not Be As Effective As Bleach Solution!!!

To Sanitize Plastic and Terra Cotta Pots and Planting Containers

You Will Need:
Chlorine Bleach (unscented)
Measuring Cup or Gallon Milk Jug (See above Hint #2)
Warm Water
Large Bucket, Basin or Kitchen Sink (for soaking)
Unscented Dish Soap
Scrub Brush or Old Tooth Brush
Steel Wool (for tough to remove mineral/salt deposits)
Rubber Gloves

·      Soak pots and planting containers in warm, soapy water to loosen fragments of matter.  Use a scrub brush to scour the pots clean, scrubbing off any debris as well as those nasty mineral/salt deposits. 
·      Use Steel Wool for difficult to remove stains and rinse with warm water until all the soap runs off.
·      Make a bleach solution: 1 part bleach to 9 parts water (see above for more info.)
·      Completely submerge pots and planting containers in solution and soak for 10 to 15 minutes. 
·      Upon removing the containers, rinse with warm water. 
·      Scrub lightly with soapy water (using unscented dish soap) and rinse well until soap runs off and water runs clear. Inspect for remaining residue and repeat procedure if necessary. 
·      Lay containers out to dry for 24 hours before using.  If possible, dry pots in direct sunlight.  Exposure to the sun can also help to kill off certain bacteria. 

NOTE:  If stains or heavy residue still remain after the sanitation process, it is not recommended to re-use the pot. Discard any materials when sanitization is unsuccessful. Some plastic pots can be recycled.  If you’ve stored containers or flats from your local nursery, you can often return them.  When I cannot sanitize a terra cotta pot, I break it into pieces and bury them in the backyard, away from the garden and ornamental shrubs.

To Sanitize Garden Tools
You Will Need:            
Chlorine Bleach (unscented)
            Measuring Cup or Gallon Milk Jug (See Above - Hint #2)
            Warm Water
            Large Bucket, Basin or Kitchen Sink (for soaking)
            Unscented Dish Soap
            Steel Wool or Wire Bristled Brush (for rust build up)
            Rubber Gloves

·      Soak tools in warm, soapy water to loosen fragments of matter.  Use steel wool or a wire bristled brush to scour the tool, scrubbing off any debris or rust spots.
·      Make a bleach solution: 1 part bleach to 9 parts water (see above for more info.)
·      Completely submerge tools in solution and soak for 10 to 15 minutes.
Hint:  If the tool is cumbersome or oddly shaped, and you cannot soak it, try filling a spray bottle with the fresh bleach solution.  Spray the entire tool to the point of saturation (until solution is dripping from the tool).  Allow to stand for 20 to 30 minutes before moving onto the next step.
·      Upon removing the tools, rinse with warm water. 
·      Scrub with soapy water (using unscented dish soap) and rinse well until soap runs off and water runs clear. Inspect for remaining residue and repeat procedure if necessary.  Ensure all the bleach has been rinsed off (bleach is corrosive and will cause rust if left on the metal of your tools).
·      Lay tools out to dry for 24 hours. If possible, dry in direct sunlight. Exposure to the sun can also help to kill off certain bacteria, and will help your tools dry completely – small areas around hinges or other joints will collect water, and if not dried properly, or if bleach remains, both conditions will cause rust to form on your tools. 

NOTE: When you are finished drying your tools, oil them before putting away.  Use machine oil or penetrating oil.  Dip a dry cloth into the oil and rub onto all metal areas of the tool.  Rub as if you are applying stain or oiling a pan for baking.  Use a dry cloth or go over the oiled areas to remove excess.  

To Pasteurize Potting Soil for Re-Use
You Will Need:
An Oven or An Outdoor Grill
High Heat Thermometer
Old cookie sheets

·      Preheat your oven to 180 degrees Fahrenheit. 
·      Spread several inches of dry soil across the cookie sheet.  Do not overload the pan, but utilize the space.
·      Place cookie sheet full of soil into oven. 
Hint:  Heating soil inside an insulated oven can leave an odor for several days after the process is complete.  To help prevent smell, heat oven to 200 degrees instead of 180 and leave the oven door slightly ajar during the heating process then place a box of baking soda into the oven once cooled, or try open broiling fresh lemons in a pan of water to kill the stench.
·      Use your thermometer to take readings of the center of the soil every few minutes.  When the soil temperature reaches to 212 degrees Fahrenheit or above, most soil borne organisms cannot survive and the soil is considered sterile for all standard potting purposes. 
·      Remove soil from oven and place out to cool, keeping soil on cookie sheet. 
Hint:  Pasteurizing potting soil will kill all organisms – good and bad.  Before re-using sterilized potting soil, combine organic matter, compost, or slow release fertilizer according to directions in order to rejuvenate you’re potting mix and replace necessary minerals and helpful organisms.  Note that fertilizer can create higher amounts of salt deposits.  Bone meal, blood meal and compost are less likely to contain harmful salts.

Outdoor Grilling Method:  An outdoor grill works as well as an oven, and will prevent the strange, earthy smell that cooking soil produces from contaminating your house for 48 hours. Purchase or re-use large aluminum roasting pans, fill with old soil, cover and place on the grill until temperatures reach 212 degrees Fahrenheit. Stir once to encourage the soil to heat evenly. Remove, cool, and mix in your organic matter to rejuvenate the soil.

Boiling Water Method: Boiling water can also kill off most of the harmful organisms lurking in your old soil.  Try poking holes in the bottom of a large storage container, paint bucket, or other plastic container.  Fill 2/3rds of the way with your old soil.  Boil enough water to pour continuously over the entire mass of soil.  Pour the boiling water into the container until the soil becomes muddy. Be sure to place your container in a location where the boiling water can safely drain out through the holes at the bottom of your container.  A few large stones along the bottom of your container will help with drainage if the soil is very fine and clogs the holes.  Place in the sun, covered with black plastic (a cut up garbage bag will do).  When it is dry, mix in a little organic matter and use.   

To read more about sanitization and pasteurization methods, check out the extension links and websites below:

The National Garden Association has a website full of helpful hints and information according to region.  Check them out at