When it comes to mold, it helps to know your foe

This yellow New Zealand tomato barely survived the mold that attacked its neighbor to the left. Much of the branch was cut away, and carefully, to avoid causing an explosion of spores. 

Funny how this happens, but two events from last week triggered today’s column:

Event #1: A comic strip in Wednesday’s Kodiak Daily Mirror:

One of the characters is looking in the fridge and says, “What’s the purplelish-green stuff in your fridge?”

“Jell-O mold mold.”

Event #2: I discovered gray mold on my green tomatoes. 

Something was in the air. 

Something was in the air alright: mold. After a few days of alternating rain and sun, conditions in the hoophouse were perfect for gray mold to explode on tomato leaves and stems, causing some of my cherry tomatoes to lose their grip and fall to the ground.

What’s a gardener to do?


First of all, mold is found on a vast range of plants. Mold is more than a thing. It’s a fungus, a disease called Botrytis cinerea. And while it might be gray and innocent-looking, it’s able to travel at lightning speed through gardens — infecting plants in outside beds and in greenhouses and hoophouses. This is especially true during damp weather, warm or cool.

How can you identify it? Mold appears as gray, soft, mushy spots on leaves, stems and flowers. The spots often become covered with a coating of gray fungus spores, especially if humidity is high.

The disease easily affects plants that are already damaged or beginning to die. Spores develop when conditions are optimal and are transported by wind, hands, tools, clothing or splashing water onto blossoms or young leaves, where they germinate and enter the plant. It can spread like tiny bulls on a rampage and can cause extensive damage to healthy parts of plants. But that’s not all …

I’ll bet everyone reading this sentence has met mold before: on store-bought strawberries, inside heads of lettuce, on oranges, bread ...

So where does mold come from?

Gray mold overwinters on plants or in the soil. Yikes! That’s why it is critical to clean seedling containers and greenhouse interiors at the end of the season. 

Spores require cool temperatures (45 to 60 degrees) and high humidity (around 93%) to germinate. Which means, during periods of drizzle and fog, check your plants frequently. Look under, over, behind, on top ...

Another thing to remember: Germinating spores rarely penetrate healthy, green tissue directly, but enter through wounds caused by broken stems or pruning.

How do you prevent and stop gray mold?

 It sounds like a science fiction movie script, but as I hinted at before, gray mold exists most everywhere — in the air, on surfaces — just waiting for the right conditions to “bloom.” Whether you’re transplanting seedlings, watering a hanging basket or taking care of someone else’s houseplants, these tips will help prevent a mold infestation:

Remove faded flower blossoms and fallen petals. As you do this however, be aware of spreading spores. Move slowly, and frequently dip your hand tools into a mild ammonia-water, vinegar-water or essential oil-water solution made from doTerra’s On Guard. In the greenhouse, where it’s common to grow tall sunflowers and poppies, this means cleaning up petals that fall onto plants below.

In the vegetable garden, remove infected plants immediately after harvest. Plant tissues that are stressed, crimped, ripped or not actively growing are great hosts for gray mold to find a footing. Rhubarb plants are especially susceptible to mold at the end of the season.

Improve sunlight and air circulation. For one thing, don’t crowd plants. In greenhouses and hoophouses, the less air circulation you have, the greater the chance of developing mold. Vents that open automatically on hot days are not enough. You need fans that run 24/7. One of my favorite ways to increase air flow in the hoophouse is to hang an oscillating fan upside down and let it spin back and forth, back and forth.

Speaking of fans, make sure nothing is blocking fan-breezes. Case in point: Mold formed on my tomato plants because a tall marigold was blocking air movement. 

On overcast days, do NOT close doors and windows to your greenhouse thinking you need to preserve heat. According to Elana White of Strawberry Fields Nursery, shuttering up your plants in cool, calm air is one of the worst things you can do.

Avoid overhead watering, especially late in the day. Keeping foliage dry is extremely important to control this disease, so water the soil, not the plant. 

Clean your greenhouse or hoophouse as best you can at the end of the season. Remember, gray mold can over-winter in the soil, in decaying plant debris and on infected dead plant material.

Sterilize plant containers with a mild bleach or vinegar solution before re-using them.

The bottom line: If you spot gray mold in your garden or hoophouse, take care of it quickly. But remember, keeping your plants healthy to begin with is your best defense. 

Back to the cartoon strip ... While I don’t eat Jell-O, the message made me laugh and think of my brother, Alby. With five kids in the house, the refrigerator saw a lot of use. One time, I was poking around the fridge, looking for a snack. 

“Ewww, what’s this?” I shrieked.

Without hesitation he said, “Looks like a case of Refrigeratus neglectus.” 


Get Marion’s free Photo Tips PDF, a collection of her favorite photography tips, on her blog at MarionOwenAlaska.com. Connect with Marion: Facebook and Instagram or send an email to Marion at mygarden@alaska.net.

(0) comments

Welcome to the discussion.

Keep it Clean. Please avoid obscene, vulgar, lewd, racist or sexually-oriented language.
Don't Threaten. Threats of harming another person will not be tolerated.
Be Truthful. Don't knowingly lie about anyone or anything.
Be Nice. No racism, sexism or any sort of -ism that is degrading to another person.
Be Proactive. Use the 'Report' link on each comment to let us know of abusive posts.
Share with Us. We'd love to hear eyewitness accounts, the history behind an article.