Gardening with Xpress: A time to kill and to water

Green greetings! As it really warms up, I hope you’ve been enjoying baskets of goodness from your gardens. This month’s questions were, unsurprisingly, about bugs and water — two major themes of summertime gardening.

A reminder to email me your questions at [email protected]. I look forward to hearing from you!

Fat little green caterpillars are munching my kale, what can I do?

Ah yes, it’s pest season again in the garden. The fat little green caterpillars enjoying your juicy kale are the larvae of a small gray and brown moth, Trichoplusia ni, more commonly known as the cabbage looper. They have a particular fondness for any plants in the brassicaceae family (also known as cruciferous or cole crops: kale, collards, cabbage, broccoli, cauliflower, etc.).

Indeed, they get their green color from the foliage they consume. As a result, they’re infuriatingly camouflaged in the midribs of most leaves, so you may not notice them until holes start appearing in your crops! You may also be dealing with black, yellow and white striped caterpillars that do similar damage; they’re the larvae of “cabbage white” butterflies, Pieris rapae.

The cabbage looper is a fair weather pest and can’t survive in temperatures below about 50 degrees Fahrenheit. Once things really warm up, they’re off and running, completing up to five life cycles per year here in the mountains. When it cools down again in the fall, they head south to balmier climes.

So, my first piece of advice for managing this pest is to plant the crops it loves in the early spring, and again in midsummer for fall and winter harvests. Yes, this means no kale in the summertime, but there are plenty of other garden goodies that love hot weather, so it won’t be too terrible. Plus, kale gets bitter and pungent in hot weather, so summer kale isn’t that tasty anyway.

Other methods of dealing with this little wiggler are: hand-picking and spraying an organic pesticide called Bt.

If your garden is fairly small, you can simply stroll through it and pick them off every few days. (Just make sure you check the undersides of leaves and look carefully, since they’re so well camouflaged.) To dispatch the collected cabbage loopers, squish them, dunk them in soapy water or feed them to your chickens.

Another tool to reach for is Bacillus thuringiensis, or Bt. This is a naturally occurring bacterium that’s found in soils and on plant leaves around the world. When you buy a bottle of it, it comes from a lab. If caterpillars of any kind, including cabbage loopers, ingest Bt, they die. Humans, on the other hand, can consume Bt with no problem, as can honeybees, ladybugs and even adult cabbage loopers; it’s specific to caterpillars.

Bt is approved for use in certified organic operations and considered safe. It’s still a pesticide, so let’s not go crazy spraying it hither and thither. If it gets on milkweed, for example, it will kill the monarch butterfly larvae that feed on that plant.

In my opinion, organic gardening isn’t just about replacing synthetic inputs with organic ones, it’s about working cooperatively and humbly with the cycles of the living world. So, Bt is awesome, and I use it, but I use it judiciously; I also don’t insist on growing kale all summer long or try to grow long-season brassicas like brussels sprouts because that would mean spraying a lot in our area.

I typically spray Bt a few times in the late spring/early summer to get my cabbage and broccoli through to the finish line of maturity and extend the kale harvest just a wee bit. Then, in midsummer, I spray a few times on baby brassicas so they can make it into cooler weather without getting eaten.

When and how often should I water my garden?

One of my online gardening class students recently asked me about watering, too. She said that her grandparents never watered their garden, and she was wondering if that would work today (she’s located in this area).

The short answer is no. While we’re still blessed with significant rains, babbling brooks and sweetwater springs, we aren’t immune to climate change here in WNC. Even in the short nine years I’ve been gardening here, I’ve noticed significantly less rainfall, and the rain that does fall comes more sporadically, with longer dry spells in between. This all makes regularly watering the garden crucial.

How often to water a garden depends on several factors and ranges from twice a day to once a week, or never if it rains a lot. If you’re directly sowing crops like carrots, cilantro, dill, beans or lettuce in your garden, you’ll want to water at least once a day until they pop up. On very hot and sunny days, twice is better. After that, watering every couple of days will likely be fine until the little plants get established. Other factors that influence watering frequency are type of crop, weather and if the soil is exposed or covered with a mulch layer, which reduces evaporation.

One important thing to keep in mind is that long, deeper watering is much better for your soil and established plants than quick, shallow waterings. This means taking the time to water thoroughly once or twice a week is actually more effective than watering daily. If we get a big rain, of course, that counts as watering.

But don’t be fooled! Afternoon thunderstorms may feel dramatic, but sometimes the actual amount of rainfall they provide doesn’t moisten the soil very deeply. When in doubt, dig down to see if your plants got a real drink or just a cooling shower.

The ideal time for watering a garden with overhead irrigation like a sprinkler or water wand is usually early in the morning. This is because less water will evaporate into the cool morning air. Plus, if plant leaves get wet in the morning, they won’t stay wet long enough to harbor fungal pathogens like powdery mildew. If you water in the evening, most of the water goes into the ground and doesn’t evaporate, but if plants remain wet all night this can cause problems.

Watering in the middle of a sunny day will mean you’ll lose some water to evaporation. Another disadvantage of high-noon watering is that water droplets on leaves can act like magnifying glasses and concentrate sunlight to the point of burning. However, it’s better to water on a sunny day than not to water at all. When it’s overcast, you can safely water any old time.

If you’re watering a garden with drip irrigation, there’s more flexibility with timing. You can water anytime, even in the middle of a hot sunny day. In fact, watering at this time with a drip system can reduce stress on plants in the height of summer, when temperatures and transpiration soar.

If you’ve been enjoying this feature and want to learn more from me and my co-instructor, Natalie Bogwalker, I invite you to sign up for our free class on summer planting for fall and winter harvests. It’s available from July 1-15. There are lots of vegetables you can grow in the fall and winter, extending the harvest and enjoying new flavors that don’t do well in summer’s heat. Many gardeners get started too late on fall and winter planting; midsummer is actually the time. Learn what to plant, some gardening basics, tricks for fall and winter success and how to set up a row cover.