Remember Slurpy Day in elementary school? It was the one day of the week when the Powers That Be allowed the Slurpy machines in the cafeteria to be turned on. 

You and your friends spent the entire lunch getting bright blue tongues and "ice cream" headaches.

Afterwards, during class, you felt more like running around the room or punching the boy in the next seat than listening to the teacher.

Your friends felt the same way. Giddy. Restless. Edgy.

Before the school day was through, somebody always got into trouble.

And although you took your punishment like a good little girl or boy, you knew what was really to blame: that yummy amalgamation of icy sludge that set your system humming and thrumming for hours, out of control on an artificially
induced high—the Slurpy Effect.

The Slurpy Effect on kids is a lot like the influence chemical fertilizers have on plants, causing them to grow and
grow and bloom, bloom, bloom unnaturally to the point of exhaustion.

Like a second grader on Slurpy, all that frenzied activity is bound to get plants into trouble. Inevitably, they fall into a weakened state that leaves them open to disease and vulnerable to pest damage.

Every spring I plant marigolds.  

For me, as for many gardeners, it's a tradition.

Since their introduction to Europe in the 16th century, marigolds (Tagetes spp.) have been a staple in home gardens around the world, and as early as the 19th century, writers have referred to them as "old-fashioned" flowers.
 
French marigolds (Tagetes patula) were my father's favorites, and at the house where I grew up, my mother and I would sow them each spring from seed we'd collected the previous year, crushing the dried flower heads and scattering them, chaff and all, in a row by the carport. (She saved the shriveled seed heads whole in paper bags.) 

By summer our marigolds had formed a thick, bushy hedge. 

Like my father, I liked their smell and their cheery orange, red and yellow flowers. 

It takes several hard frosts to kill French marigolds, so they're among the few summer flowers that still look good in a fall garden. For this reason, they are indelibly linked in my mind to chilly back-to-school mornings, windfall apples and chrysanthemums.

These days, I sow them outdoors in spring and summer, scattering saved seeds and sprinkling them lightly with soil before giving them a thorough shower of rain barrel water.  (Unlike Mom, I separate the seed from the chaff before storing it.)

I like to grow French marigolds potager-style, mixing them in flowerbeds and raised beds alongside vegetables, small fruits and other flowers.

Although I've read that marigolds are sometimes prey to spider mites, ours are virtually pest-free, suffering only minor snail damage on the leaves now and then.

Like most gardeners, I prefer the aromatic variety. (Odor-free marigold hybrids have never been popular.)

Studies conducted through the  University of Georgia,  University of North Carolina, Wisconsin University and others have shown that French marigolds reduce the number of nematodes (a.k.a. microscopic worms) in the soil that cause root lesion disease and root knot disease.

How do marigolds do it? Their roots and leaves naturally produce terthiophene and other compounds that are toxic to disease-causing nematodes.  

Some varieties of French marigolds produce more toxins than others. 'Tangerine', 'Petite Gold', 'Petite Harmony', 'Goldie', 'Nemagold,' and 'Nema Gone'  are just some of them. 

Other species of Tagetes, including the much taller African marigold (also called the American marigold) produces natural pesticides, too.