How to Get Rid of Powdery Mildew: Organic Treatment and Prevention

By Deanna Talerico updated Jun. 29th, 2026, published Apr. 29th, 2021

Come learn how to get rid of powdery mildew in your garden. I live in an area where powdery mildew is incredibly persistent, so I’ll share my top tips to prevent mildew, reduce its spread, and the organic treatment methods I use to keep my garden looking beautiful, healthy and productive.

I’ve also included how to identify powdery mildew, its favored conditions, and what plants are most susceptible (or resistant!) to help you better manage it. Or, skip straight to the prevention and treatment options here.

What is Powdery Mildew?

Powdery mildew (also known as “PM”) is a common fungal disease that can affect a wide variety of edible crops, flowers, and ornamental plants. Though it goes by one collective name, powdery mildew can be caused by several different species of fungi.

Powdery mildew appears as white powdery mold spots on plant leaves. As the fungus feeds and robs nutrients from the plant, it causes stunting and reduced vigor. This stress can also make the plant more vulnerable to other diseases or pest damage.

If powdery mildew coats a significant portion of leaves it can inhibit photosynthesis – slowly starving the plant. A change in photosynthesis can also negatively impact crop flavor as the plant produces less sugars.

A close up image of a squash plant with a heavy infestation of powdery mildew. The leaves are caked with a whitish silver coating that resemble spray paint. — A very severe case of powdery mildew on zucchini in my neighbor’s garden. Do NOT let mildew get this bad in yours! (I would treat or remove the plant far before this stage)

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Ideal conditions for PM and how it spreads

Powdery mildew can be found in virtually every growing zone, though it especially thrives in climates with prolonged periods of warm dry weather with a touch of humidity. The dampness of humid air (or evening fog/dew) encourages the fungi to grow, and the warm dry air during the day helps the spores spread.

Powdery mildew spores primarily live on plants, but can also survive or overwinter in soil, compost, mulch, or other plant debris. The spores spread from plant to plant (or, are initially introduced into your garden) by wind, insects, splashing water or direct contact from infected plants.

Crowding plants, lack of airflow, and shade also increase the risk for powdery mildew.

A watering can that isn't visible is watering the soil below the canopy of collard greens so the water isn't getting on the plant's leaves. The water resembles that of a rain shower spray. — Providing good airflow between plants and avoiding wetting plant leaves helps to reduce the spread of PM.

Identifying Powdery Mildew on Plants

Powdery mildew appears as light grey or white, dusty-looking spots or blotches. The spots are usually round, fuzzy, sometimes slightly raised, and typically start on leaves and stems before moving to the flowers or fruit themselves. The infected leaves may eventually turn yellow and dry out too. In severe cases, the plant looks like it’s been dusted in powdered sugar or flour.

Powdery mildew is sometimes confused with downy mildew, which causes darker yellow-brown spots on leaves instead.

Keep in mind that natural leaf patterns can sometimes look a lot like mildew too! Some varieties of zucchini, squash, and melon plants have natural white spots or variegation on their leaves. (See example photo below.) If you need help identifying the difference between powdery mildew vs natural white spots on leaves, see this post.

A small cucumber seedling is showing small splotches of powdery mildew on its leaves. Two small yellow flowers are emanating from the main stem below the leaves. Powdery mildew favors plants in the cucurbit family. — Powdery mildew spots on cucumber leaves

A two part image collage, the first image shows the top leaf of a PM resistant variety of squash. There are natural gray variegation on the leaves that are fairly symmetrical across the whole leaf. The second image shows DeannaCat turning the leaf over so you can see the underside which looks green and healthy where as plants inflicted with PM will usually have spots on the undersides of their leaves as well. — This is a perfectly healthy zucchini leaf, believe it or not. It just happens to have a natural variegated pattern that resembles PM at first glance.

What plants get powdery mildew?

Powdery mildew can inflict over 1000 different plant species including many common vegetables, flowers, and ornamental plants.

Plants that are especially susceptible to get powdery mildew include squash (both summer squash like zucchini and hard squash such as pumpkins or butternut), melons, cucumbers, tomatoes, eggplant, peppers, kale, peas, beans, lettuce, strawberries, grapes, mustard greens, carrots (the greens), apple trees, and many flowers including zinnia, calendula, roses, sunflowers, peonies and hydrangeas.

I’ve found that cabbage, cauliflower, broccoli, bok choy, and collards may get a little PM, but not nearly as bad as the aforementioned plants.

Some plants that are resistant or do not readily get powdery mildew include avocados, citrus trees, garlic, and many herbs – including basil, sage, lavender, rosemary, thyme, oregano, dill and more.

A large Dunja zucchini variety plant is featured. It's leaves are more than twice the width of a large hand. Many green fruit are growing amongst its base with a few flowers mixed in as well. Surrounding the squash are many calendula and borage with yellow and purple flowers. Beyond in other raised beds lie onions, collard greens, an array of calendula flowers, pole beans and zinnia. A wall of flowering salvia make up the background with pink flowers dotted amongst the green foliage. — Another perfectly healthy squash plant with natural leaf patterns that look similar to PM. In fact, this Dunja zucchini variety is resistant to powdery mildew – a prized cultivar in our summer garden.

7 Ways to Prevent Powdery Mildew

Here are several ways I’ve found help prevent powdery mildew in my garden. In fact, they’re often so effective at keeping it to minimum that I rarely need to treat for it!

Choose plants and varieties that are naturally resistant to powdery mildew. Reading plant descriptions or seed packets, you can find many varieties of mildew-resistant zucchini, melon, tomatoes, zinnia and more. They won’t be totally immune but are effected far less. For instance, Dunja is my go-to zucchini variety – it rarely gets mildew, while most squash in our garden does.
Practice good plant spacing. PM thrives in humid, crowded conditions. Prevent powdery mildew from spreading between plants by reducing overcrowding. Follow spacing recommendations for each type of plant, and prune plants as needed to increase airflow and reduce touching between them. Mildew also grows most readily in the shade, so provide susceptible plants plenty of sunshine.
Don’t compost diseased plants. Instead, put them in the trash or municipal green waste bin. Powdery mildew spores can survive in your compost and will spread to other areas of your garden when you use the compost later.
Clean your garden tools! It’s always a good idea to routinely sanitize your garden tools (e.g. pruning shears), especially when you’re working around diseased plants. To prevent powdery mildew from spreading, I always use rubbing alcohol, white vinegar, hydrogen peroxide, dilute bleach, or another sanitizing agent to wipe down tools before moving on to the next plant.
Wet the soil, not your plants! As much as possible, avoid watering plants overhead. Constantly damp leaves or splashing water from an already-infected plant encourages the growth and spread of powdery mildew. Instead, water the soil below the plant. Get my guide on how to install drip irrigation for raised garden beds here.
Use companion planting and crop rotation. If you know you struggle with powdery mildew, don’t plant a bunch of plants that are highly-prone to PM all together in one bed. Buffer and interplant them with resistant species. Learn more about garden companion planting here – printable chart included! It’s also important to practice crop rotation, especially after a bought of PM.
Promote overall healthy plants and immune systems. Healthy, well-nourished plants are more resilient to fend off disease – including mildew. To keep my garden happy and healthy, I routinely amend our garden soil with organic fertilizers and well-aged compost, and water with homemade compost tea and aloe vera extract. Develop a consistent watering schedule and avoid drought stress too.

Raised garden beds are set against a greenish blue house, the beds are lush with a variety of plants growing in them from chard, to calendula, to pole beans growing up a metal trellis. Zinnia and sunflower plants are growing up towards the setting sun while more calendula and borage is growing along the ground in front of the beds leading to a dazzling array of flowers that are purple, pink, orange, and yellow. Prevent powdery mildew by maximizing companion planting. — An example of wise companion planting: Swiss chard (usually resistant to powdery mildew, at least in our garden!) sandwiched between pole beans and calendula in back and front – two crops that are very prone to PM. Planting other susceptible crops like bush beans, kale, collard greens, or eggplant in the place of the Swiss chard would have been asking for trouble.

5 Ways to Get Rid of Powdery Mildew

Now, here are 5 organic ways to treat or get rid of powdery mildew. There are all sorts of other “hacks” out there, but these are the most effective options in my experience. (I’ve tried the suggestion of spraying plants with milk… and all it did was make my plants smell like rotten milk.)

Cut and remove infected leaves. If caught early enough (and as long as the plant can survive without the infected part) the simple act of pruning off a few infected leaves can often halt or drastically slow the spread of powdery mildew to the rest of the plant. Just be sure to clean your pruning shears well before and after!
Spray the plant with baking soda. Sodium bicarbonate (baking soda) changes the pH of the leaves, making them more alkaline and less hospitable for the fungus to thrive. Thoroughly mix 1 to 2 tablespoons of baking soda per 1 gallon of water plus 1 tablespoon of liquid castile soap or dawn dish soap (which helps the baking soda spread and stick to the leaves better) and then spray the plant down, saturating both the tops and bottoms of leaves.*
Use potassium bicarbonate. This is the most effective organic treatment for powdery mildew I’ve found! Potassium bicarbonate has a similar method of action to baking soda (raises pH to inhibit spore growth), but is even stronger and longer-lasting. Once I treated young seedlings that developed mildew very early on, and after just one application they stayed PM-free for the rest of growing season! Mix 1 Tbsp of potassium bicarbonate powder and 1 Tbsp of liquid soap in 1 gallon of water. Add it to your favorite sprayer, shake it all up, then spray everything down – coating all parts of the plant.*
Neem oil spray – In my experience, neem oil slows down the spread of powdery mildew, but doesn’t usually cure an established infection. I personally don’t love to use neem oil directly on tender foliage that I’m going to eat (like kale leaves) or veggies with a lot of nooks ‘n crannies (such as broccoli) because it can leave an oily residue that isn’t always easy to wash off. However, it’s great for for the leaves of squash plants! Neem oil must be diluted and applied carefully*. Learn exactly how to properly emulsify, mix, and use neem oil spray here.
Trash infected plants. If all else fails, it is best to completely remove significantly infected plants from your garden to stop the spread of disease. Use caution and common sense during removal: avoid shaking the plants about, dragging them over other plants or prime soil, or anything else that would cause the fungi spores spread even more. Remember, don’t add these to your compost heap.

*For any type of foliar spray treatment, I always recommend waiting to apply it until the evening hours – once the plant is out of direct sunlight. Bright sun on wet leaves can cause scorching. Also, beneficial insects are typically less active during the evening to dusk hours. Though all of these treatment options are considered safe and organic, it’s best not to directly spray beneficial insects with them.

A pump sprayer is sitting on the corner of a raised garden bed, Aaron's hand is reaching into the image holding the wand of the sprayer as he applies a foliar spray to prevent or treat powdery mildew onto bush beans that are growing in the raised bed. There are other plants in the bed including more bush beans and kale. In another garden bed next to it there are tomatoes, peppers, and onions growing. The evening sun is just about setting below the horizon as a yellow orange glow recedes amongst the shadows. — Spraying down mildewy bush beans with potassium bicarbonate.

Can you eat vegetables that have powdery mildew?

In general, powdery mildew isn’t harmful to people. Meaning, it is not toxic or poisonous. Although, some folks are sensitive or even allergic to mildews and mold, so it’s wise to proceed with caution.

Since mildew is quite common in my garden, I’ve definitely eaten plants with a few spots of mildew! (I hate the idea of wasting food). I simply wash the produce well before eating it, but avoid consuming severely infected parts.

DeannaCat is holding a leaf of lacinato kale that has be inflicted with powdery mildew. The raised white and fuzzy growth is stretching across the length of the leaf. — Here is a moderate case of powdery mildew on kale leaves. Also note the smaller white spots on the leaves in the background. I would personally not eat leaves with this much mildew on it.

And that concludes this lesson on organic powdery mildew management.

All in all, don’t worry if your plants get a few spots of mildew. It’s almost to be expected! We’ve learned to accept and peacefully co-exist with the relentless fungi in our garden, yet do try to be proactive about keeping it to a minimum. I hope this article gave you plenty of ideas of how to do just that. Feel free to ask any questions in the comments below.

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53 Comments

Jacqueline

August 27, 2022 at 4:58 am Reply

Very humid here in NC and tons of PM. Does it overwinter in soil? If so, can I treat the soil and is there a cover plant I could use for winter that would give any benefit? Thanks for your time!
- Aaron (Mr. DeannaCat)
  
  August 27, 2022 at 8:41 am Reply
  
  Hi Jacqueline, be sure to clean up any leaf or plant debris in your garden to lessen the chances of the mildew staying around. PM is something that has to be managed as chances are, it will just come back the following year, we get PM here in various ways every season no matter what so it is just something we have to manage. We do this by planting PM resistant varieties of vegetables when possible, clean up all extra plant and leaf debris that falls on the garden soil, you can use micronized sulphur mixed with water to treat infected plants, or use potassium bicarbonate which helps but doesn’t work as well as the sulphur. I wouldn’t be concerned with treating your soil specifically, this article by Rodale Institute covers the benefits of planting hairy vetch cover crop for PM suppression of cucurbit vegetables. Hope that helps and good luck!
Judy

August 20, 2022 at 4:59 pm Reply

Hi. I’ve noticed a bit of powdery mildew starting on my calendula plants. I first harvested all the fully opened flowers as I’m planning to follow instructions and make calendula salve. I then sprayed all the plants with a combination of potassium bicarbonate as you suggest. My plants are loaded with flower buds.
My question is .. can the potassium bicarbonate affect the quality or chemistry of all the buds remaining on the plant? Will it be ok to use those sprayed buds once they fully open for the salve? This is my first time making any salve so just want to be sure it will be safe to harvest and use. Thx.
- Aaron (Mr. DeannaCat)
  
  August 21, 2022 at 8:31 am Reply
  
  Hi Judy, your flowers should still be fine to dry and use in your salve, it is approved for organic gardening and it can even be used up until harvest. Hope that helps and enjoy your salve.
  - Judy
    
    August 21, 2022 at 9:29 am Reply
    
    Thank you! I’m following your calendula salve instructions which is what inspired me to grow calendula. Never heard of it before and now my backyard is filled with so many pretty blooms. You have been so very helpful in all the questions I have asked. Thank you again! 🙂
gabriele holland

May 27, 2022 at 12:53 pm Reply

trying to make a copy of your great information to my computer for future refference. HAVE ANY IEAS?
- Aaron (Mr. DeannaCat)
  
  May 28, 2022 at 7:50 am Reply
  
  Hi Gabriele, our site doesn’t allow for easy printing or copying of the information unless it’s a printable recipe. I would suggest you bookmark the posts that are of most interest to you in your web browser so you can easily access them at a later date.
Aki

May 22, 2022 at 5:15 pm Reply

Hi! This my second year growing Calendula, inspired by Homestead and Chill! They’re doing soooo well this year, but as they’re just about to bloom I noticed that they have a really bad case of PM. How do I save my beautiful calendula plants? Would the potassium bicarbonate be the best option? I have tried to pull most of the base leaves to try to save it… Thank you!
- Aaron (Mr. DeannaCat)
  
  May 23, 2022 at 8:26 am Reply
  
  Hi Aki, unfortunately calendula is prone to getting powdery mildew and potassium bicarbonate may be your best option now. Apply the spray once a week and see if it cuts down on the mildew, make sure your plants have plenty of space and airflow/circulation which can help cut down on the PM as well. Good luck and hopefully you can get the mildew under control.
- Diana
  
  May 26, 2022 at 1:14 pm Reply
  
  Ditto! I too was inspired by Homestead and Chill to grow calendula. This is also my second year growing calendula and my first year from seeds. Thank you so much for asking the question. I’ll be spraying the plants with the baking soda solution this evening! Happy growing! Thank you Homestead and Chill for the ongoing inspiration and community!
  - Aaron (Mr. DeannaCat)
    
    May 26, 2022 at 2:30 pm Reply
    
    Thank you Diana!
Lyda

May 3, 2022 at 10:55 am Reply

Hello! Thank you for this post. Do you spray with baking soda in the evenings? And how often?
- Aaron (Mr. DeannaCat)
  
  May 3, 2022 at 11:44 am Reply
  
  Hi Lyda, we don’t use baking soda specifically but you want to spray after the sun has gone down for the day. Once a week should work as a preventative measure but you can do it twice a week if you have a heavy infestation. Hope that helps and good luck!
Jenessa

July 5, 2021 at 8:35 am Reply

Hi Deanna and Aaron,

I bought some potassium bicarbonate to treat powdery mildew on my cantaloupe and cucumber plants. How often should I spray them with the potassium mixture?

Thanks so much,

Jenessa
- Aaron (Mr. DeannaCat)
  
  July 5, 2021 at 8:49 am Reply
  
  Hi Jenessa, spraying once every week or two is usually sufficient for preventing mildew but if you currently have an outbreak I would spray at least twice a week until you get the mildew under control. Hope that helps and good luck!
  - Jenessa
    
    July 5, 2021 at 3:13 pm Reply
    
    Thank you!
Kathleen Jackson

June 30, 2021 at 4:29 pm Reply

I would very much like to know the name of the gray/silver plant on the cover of your book about powdery mildew. I know there are many types of this plant but the leaves on this plant are the same as the plant in my garden except that I cannot find it anywhere in plant stores.
Do you have its name? Thank you very much.
- Aaron (Mr. DeannaCat)
  
  July 2, 2021 at 8:46 am Reply
  
  Hello Kathleen, that is an unknown variety of summer squash that our neighbor was growing, likely a zucchini of some sort.
Eunice Olson

May 5, 2021 at 12:20 pm Reply

This is not about powdery mildew! I live on the Central Oregon Coast…chilly, damp, NEVER gets hot. We grow cannabis inside a greenhouse to combat mildew (as best we can). We were told that growing tomatoes in the same greenhouse as pot is a big no-no. Not sure why or which plant has problems when they are combined. We do grow tomatoes (outside, in front of a large shop where the sun radiates heat) but they don’t get enough heat to make them really sweet and wonderful like they are in CA valley. Any info about growing them in the greenhouse with pot?

I love your blog, your little farm is fantastic. Thanks so much for taking the time to do this, it is a gem!
- Aaron (Mr. DeannaCat)
  
  May 13, 2021 at 6:57 am Reply
  
  Hello Eunice, I am not familiar with growing tomatoes and cannabis together and if it is advisable or not to have both in a greenhouse together. I am sure most people say to not put the two together because there is more of a chance for pest or disease to inflict the cannabis which is most likely a monetary investment. When growing tomatoes in climates with more cool and temperate weather, it is best to choose varieties that do well in those conditions. Adaptive Seeds is a company in the PNW with many varieties of tomatoes that do well in those conditions. Check out our Growing Organic Tomatoes: How to Plant, Feed, Prune & Grow Tomato Plants article for more information. Thanks for reading and good luck on the upcoming grow season!
C.E. Corngold

May 3, 2021 at 12:45 pm Reply

Hey DeannaCat,

Love your website/blog!

About PM, might you have come across any research regarding how long PM spores survive in soil?
I’m going to spray down my soil w/potassium bicarbonate, as you suggest, but I don’t want to lower the pH too much.
I wonder how long the spores are viable?

Many thanks and thanks for your research and reliable advice (and recipes!)
Cara in Altadena/Pasadena
- Aaron (Mr. DeannaCat)
  
  May 13, 2021 at 7:57 am Reply
  
  Hello C.E., I don’t think the potassium bicarbonate will lower you pH too much, especially if you have soil that is alive and rich in organic matter as it buffers pH quite well. I think a couple of weeks is enough time for the PM to dissipate if there are no infected plants remaining as the mildew survives on living plant tissue. Thanks for reading, hope that helps and good luck!
Barbara Stollar

May 2, 2021 at 1:33 pm Reply

I have PM on my sugar snap peas. The plants are in grow bags. How can I clean the bags so they don’t infect the next plants?
- Aaron (Mr. DeannaCat)
  
  May 3, 2021 at 2:45 pm Reply
  
  Hi Barbara, check with the brand of grow bag you have and see what their washing instructions are as you may be able to wash them, you could add vinegar to the water when you wash and or treat it with the recommended treatments listed in the article. Hope that helps and good luck!