How To Stop Powdery Mildew

powdery mildew

My winter squash has what Mud Baron once described as “jock itch for plants:” powdery mildew. I’ve tried all kinds of notions and potions in the past, but this year I decided to see what the science says about powdery mildew. Our climate where I live in Los Angeles is, unfortunately, ideal for producing this vexing fungus.

IPM
Let’s begin with some condensed advice from UC Davis’ Integrated Pest Management page:

Preventative measures:

  • grow resistant varieties
  • find a sunnier spot for the vegetable garden
  • back off on nitrogen

Non-chemical approaches

  • sprinkle plants with water mid morning–add soap for more effectiveness
  • remove infected leaves promptly and dispose of them

Fungicides:

  • apply horticultural oil, neem oil or jojoba oil if the temperature is under 90° F. Do not apply any of these oils if you have used sulfur.

DIY Options
For home remedies I turned to advice from Washington State University horticulturalist Linda Chalker-Scott.

How about milk, widely touted as a powdery mildew treatment? According to Chalker-Scott the answer is yes it might work, but you may need to apply milk before powdery mildew appears. And the studies were done with whole milk, so the effectiveness of other kinds of milk have not been tested. Milk has not worked for me in the past, probably because I applied it too late.

How about baking soda? Chalker-Scott is skeptical. Baking soda has never worked for me.

Compost tea? I hate to bring it up as the topic is insanely controversial. I discovered a tempest in a compost tea pot when I tried to write a non-partisan magazine article about it. Let’s just say I ended up leaning towards the skeptical side when I looked at the evidence. Let me know if you think I’m wrong on this, especially if you can leave a link to a peer reviewed study.

Conclusions
What has definitely worked for me in the past is seeking out resistant varieties. I wasn’t smart enough to remember this fact so I’m going to try the soapy water approach and step up to something stronger if I have to. Part of my problem might also be too much nitrogen–my infected squash is in our straw bale garden and I had to apply a lot of blood meal to get it going. More sun would also help but that would involve cutting down a very large tree. I’ll update this post later in the season.

Let’s hear from you . . .
What powdery mildew treatment have you tried and how did it work? Leave a comment and join the conversation!

And I put the question out on the Root Simple twitter feed and got a few divergent opinions:

Christopher Kennedy ‏@ckpfunk Bonide’s Copper Fungicide for organic gardening. I spray every 14 days this time of year instead of every other w/ baking soda.

Alec ‏@Alec I’ve tried horsetail tea, sea-crop, baking soda, compost tea, and neem oil on mildew, but none compare to milk.

Alissa Walker ‏@gelatobaby I just sprayed with a baking soda solution seems to have done the trick so far. And removed all damaged leaves.

Alex Mitchell ‏@alexmitchelleg give the plants some air, water the ground not the leaves. Could spray diluted milk with water on leaves – never worked for me

Straw Bale Garden Update: Success!

straw bale garden

Ladies and gentleman, straw bale gardening works. I left town for a week earlier this month and, during my absence, the vegetables in the straw bale garden exploded in size. The Tromboncino squash on the left, is threatening to envelop the entire yard.  The tomatoes are equally vigorous and covered in ripening fruit.

straw bale garden zucchini

Zucchini is on the menu.

While it takes an input of outside resources in the form of straw and fertilizer, straw bale gardening is a great solution for beginning gardeners or for those cursed with bad soil. And the skunks that have decimated my previous vegetable gardens are unable to get up on the bales.

I’m considering trying another straw bale garden during our winter season. And I’m also pondering building boxes to put the bales in to make the garden look a bit neater.

Compare the straw bale garden to the depleted raised beds in our front yard:

depleted vegetable bed

I’ve talked to a lot of people about straw bale gardens since we started ours. Some things I’ve heard from other gardeners:

  • Some straw bales may be contaminated with herbicides. Do a bioassay before planting. Here’s some instructions (scroll down to the end of the article).
  • One gardener I met did not know that the bales need to be prepared by adding nitrogen–you can’t just plant straight in the bales.
  • Once the bales have been prepared you need to add fertilizer periodically. I’ve been adding fish emulsion every two weeks.

How is your straw bale garden?

And thanks again to Michael Tortorello whose article “Grasping at Straw” inspired us to try straw bale gardening.

Annie’s Annuals and Perennials

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The artist Sandow Birk once did a show depicting a fictitious war between Northern and Southern California. If that war were to be fought by plant nurseries, the forces of Northern California would have us, down here in the Southland, badly beat. There’s a few good native plant nurseries here, but that’s about it. There’s nothing quite as spectacular as Annie’s Annuals and Perennials, located in Richmond on the eastern side of the San Francisco Bay.

Entrance display. Photo: Annie's Annuals and Perennials.

Entrance display at Annie’s. Photo: Annie’s Annuals and Perennials.

Annie’s was one of the stops on the Garden Blogger’s Fling, where we got to hear Annie Hayes herself talk about her business. She noted that most retail nurseries get their stock from distant, centralized wholesale nurseries. An outbreak of late blight disease in tomatoes back in 2009 demonstrates that centralized nurseries are a great way to spread plant diseases over wide areas.

Annie’s specializes in riotous color. Many of the spectacular gardens we visited on the Fling sourced their plants from Annie’s. And in addition to unusual and rare ornamental plants, Annie’s has a great selection of edibles. It’s first time I’ve ever seen Oca (Oxalis tuberosa) outside of a book.

I had to keep a tight grip on my credit card to prevent myself from buying plants I had no way of getting home on my bike. The good news is that Annie’s does mail order. And she’s got a bunch of tutorial videos covering topics such as container planting and plant combinations. As we begin version 4.0 of our back yard garden, I have a feeling we’ll be ordering plants from Annie’s.

Disclosure: we’re always happy to write about businesses we like and support. We did not get any compensation or free items from Annie’s.

Watering 101

standing water in a bed

This is watering 101. Those of you who have been gardening for a while have probably learned this the hard way. Those of you just starting out may find it helpful.

Soil lies.

It looks wet, but it’s bone dry a fraction of an inch beneath. Or it looks dry on the surface, but it’s actually quite wet below. Or it’s wet, but only for one inch down.

The only way to find out if you’ve watered your garden enough is to stick your hand into the soil and make sure. You can’t garden without getting your hands dirty.

This is one reason why one of the most common questions, “How much do I water?” is one of the hardest to answer. The answer will vary, depending on your soil, the weather, the method you use to water, how often you water, and what you’re growing. In the end, you just have to use your hands and your common sense to figure it out. There is no formula.

In the picture above, you see the surface of the soil in one of our raised beds. This is imported soil, the kind that comes in bags. It doesn’t hold water in pools like clay soil does, it doesn’t sink in fast as it would in sandy soil. It’s actually pretty tricky to water because it seems like it should sop up water well, but I think all the organic matter in it actually slows absorption.

At any rate, I’d been watering this bed for some time with a sprinkler hose, waving it back and forth until I got bored. The water sunk in at first, then started to pool on the surface, and the pool lasted for a long time. At this point, a beginner might think she’d watered enough, but I’ve been fooled often enough before.

I reached down into the bed and scraped at the soil. A fraction of an inch beneath the wettest area, the soil was still perfectly dry. That’s what I tried to capture in the picture below–see all that dry soil? It was just beneath the surface of the puddle.  I wasn’t done watering.

dry dirt under water

In general, you need to be sure that the soil in the bed is evenly moist.  Not soggy and soppy, not dry, but pleasantly moist and springy. Over-watering can be problem as much as under-watering. If you know your soil tends to hold water, it may pay to dig before you even start watering. You may find you don’t need to water at all.

In a regularly watered bed, the deeper you dig, the more retained moisture you are likely to find, but the first few inches dry out fast. Older, deeper rooted plants don’t mind this so much if the top dries out, because they can reach deep for water, but if you’re dealing with young or shallowly rooted plants, you have to be very careful with the first five inches or so. Don’t trust your eyes. Trust your hands.

Radish Surprise

radish close

A volunteer radish–I think it is a daikon–sprouted up in a little clear pocket of our yard. We let it go, ignored it. It grew bigger, and bigger, and bigger. Usually a radish is harvested early, so we never see how big they can get.

This one got huge, then burst out into hundreds of tiny purple flowers. Hummingbirds, honey bees and all sorts of flying insects visit it all day, every day. It has become one of the queens of the garden.

The picture below is horrible. The radish plant really is quite pretty,  the equal of any ornamental flowering shrub–but as bad is the picture is, it gives you some scale. See the bales of our straw bale garden behind it?  I think it must be pulling water from there, which accounts for its size and longevity. It’s gone a little past its prime now– a couple of weeks ago the blooms were thicker.

By the way, radish blossoms are tasty food for people, too.

radish flower