Master Gardener: Marigolds - More Than Just Another Pretty Flowers
Last updated 6/15/2020 at 12:35pm
The marigold is perhaps the most popular annual flower. During planting season, the nurseries and garden centers are filled with their showy blooms. Marigolds are a compact bushy plant originating in Mexico that come in a multitude of varieties of varying sizes and color combinations of yellow, orange and red. They are great in beds, in containers or used as an edging plant. Marigolds are fairly easy to grow. They prefer sun to partial sun and like well drained to moist soil. If kept deadheaded of spent blooms, they continue to produce gorgeous blossoms throughout the growing season.
But the marigold is much more than just another pretty flower. They can be an environmentally advantageous addition to the vegetable garden. Marigolds attract pollinators; and because of their scent they are often used to deter insects. Perhaps most importantly, however, some varieties of marigolds are nematode suppressants, meaning that they can help control nematodes in the soil and minimize nematode damage to your vegetable crops. You may ask what exactly are nematodes and what damage can they do to crops.
Nematodes are microscopic organisms that feed on plant roots. They suck out liquid nutrients and can inject damaging materials into the roots of your vegetables. In some cases they can actually pierce the root of the plant and lay their eggs inside, giving the root a “knotty” look. Plants grown in nematode invested soil will not thrive. They may appear wilted, stunted and yellowish. Their roots can be galled, knotted and decayed. The plants will produce fewer and smaller fruits. Common household vegetables affected by nematodes include tomatoes, peppers, squash, cucumbers, eggplants and okra. Nematodes thrive in warmer soil temperatures (70-85) thus early spring crops can often be grown with minimal damage even in nematode invested soil.
Planting nematode suppressants such as marigolds within your vegetable garden can provide protection without negative impacts to humans and the environment. They do this by producing organic compounds that are toxic to nematodes. These compounds are released from the roots of the living marigold plants or can be increased by tilling the entire plant into the soil.
When growing marigolds as a nematode suppressant, place the plants in rows 7 inches apart with 7 inches between individual plants. Intersperse these rows among your vegetables. Allow the marigolds to grow for a minimum of two months and till the entire plant into the soil at the season’s end. Be sure to keep the entire garden, vegetables and flowers, well weeded as nematodes can multiply on weed roots as well.
A few words of caution: The effectiveness of nematode suppressants takes time and the best result will be seen the following year after they have been used. Also, not all varieties are equal. The most effective are French Marigolds (Tagetes Patula). Specifically Petite Harmony and Petite Gold have been shown to lower root knot nematode damage. At least one variety, Tangerine Gem, can actually increase nematodes. Avoid hybrid marigolds. Ask the specialists at your local nursery or garden center and avoid purchasing marigolds of unknown varieties at the big box stores.
In short, enjoy those gorgeous marigold blooms throughout the summer and feel good about knowing that they are helping your soil at the same time.
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