Question
I started marigolds in January to give away a garden club meeting this month,Everything was fine until last month and they just started to wither and die.  They were planted in clean 3 1/2 inch pots with fresh soil and placed under light in my basement.  Never over watered and have air movement from a fan 24/7, I have been growing them for 20 years and this is the first time anything like this has happened.  I am a a loss, we have check to see if there is any thing on them, no, and when we look at the roots they have gone brown.  We live in Trenton Ontario Canada, Zone 5.  to date we have lost around 30 -40 plants,  and again yesterday 3 more. if you can please help   thanks Jack

Answer
Jack,
It sounds like you had a fungus - perhaps it came from the pots even though they were cleaned, or perhaps from the potting soil.  Brown roots indicate rot, which can be caused by several fungi. Did the stems collapse at the soil line or look darker or have a "watery" appearance? If so, this is typical of rot as well.  Maybe the soil you used this year was a different formulation that held more water then before, or perhaps for some reason your basement was cooler as well, as cool, damp conditions support a variety of fungi.

It's pretty frustrating when something like this happens, I know.  I've often told my audiences that working with plants is always an adventure even if you are a long-time experienced gardener. Plants are living things and living things are quirky, aren't they?

If you could bring any remaining pots upstairs and put them in a sunny window or in front of sliders that might help.  The fan - normally very important with seedlings as you well know -  is at this point spreading the fungal spores from pot to pot. Sunshine might stop the problem in its tracks.

If you changed your potting medium from previous years you might consider going back to the one you used before or choosing another type.  I find that the brands that are very high in peat often keep seedlings too wet, and frequently the surface actually looks dry although underneath is too damp.  Sometimes product formulations change as well, so it's possible that even the product you've used in the past could be different this season.

If you re-use the pots soak them for a few hours in a large bin or clean garbage can filled with 9 parts water and 1 part bleach.

Then tell the garden club all about the Marigold Mortality and Dastardly Diseases and the fact that no matter how experienced or careful we are, the fungi may find a way!  

all the best,
C.L.
www.gardenlady.com