Late summer is both a challenging and rewarding time in the garden as we deal with pest and disease pressure but also enjoy harvesting tomatoes, peppers and summer squash on a nearly daily basis. For this week’s podcast, I’m addressing some of the biggest (and most common) summer garden challenges and answering your burning questions that have been bugging you most at this time of the season.
Joining me on the podcast is Amy Prentice, the Director of Marketing and Communications here at Agrivana℠ Media. If you’ve been listening to The joegardener Show podcast for some time, you’ve heard Amy’s name often as I have praised her for behind-the-scenes work, but this is the first time you’ll be hearing her voice.
This week’s gardening questions were submitted by my Online Gardening Academy™ Master Seed Starting and Beginning Gardener Fundamentals enrollees, a group of very engaged gardeners. I’m sure that you have had many of these same gardening questions and will benefit from this Q&A.
Controlling & Preventing Squash Vine Borers
At this time of year, squash-vine borer issues are the subject of numerous gardening questions. The first thing to understand about squash vine borer is that it is a moth larva, i.e. a caterpillar. The squash vine borer moth is a daytime moth that’s easy to spot: It’s black and red with additional black spots. Moths land on plant stems and lay eggs. Those eggs hatch into the larvae that bore holes into the stems, leaving behind sawdust-like frass. The larvae travel up the stems and vines several feet, eating plant tissue and hollowing out the vines as they go.
The moths can be captured with a butterfly net, but there is also a pheromone trap available from Arbico Organics. The pheromone trap will catch males rather than the egg-laying females. However, if you put out the trap in early summer and check it often, you’ll know when squash vine borers have arrived. When the trap catches its first moth, it’s time to take proactive measures.
One option is horticultural oil, which when applied to the stems will suffocate the eggs. You can also just scrape off eggs as you find them. And then there is Bacillus thuringiensis, or Bt.
Bt is a biological control that is available in both dust and liquid forms. Apply the dust to the base of plant stems to kill larvae before they bore into plants. If larvae are already inside the stems and vines, you can inject the plant with liquid Bt using a syringe.
Take note that Bt kills all caterpillars, whether they be butterfly or moth caterpillars, so even though Bt is organic, apply it with care. Farmers use Bt on corn earworms — they are moth caterpillars and not worms, despite the name — but the earworms are beginning to develop Bt resistance. The good news is there is an emerging control made from synthesized spider, sea urchin and scorpion venom that can be mixed with liquid Bt to overcome that resistance. It is known as Spear-T.
Zucchini and other summer squash are unfortunately very susceptible to squash vine borer. However, this pest prefers hubbard squash (Cucurbita maxima) most of all. You can plant a trap crop of hubbard squash, which is a winter squash, to draw squash vine borer moths away from your summer squash and spaghetti squash.
A winter squash that squash vine borers leave alone is butternut squash (Cucurbita moschata). The vines of butternut squash are solid, so the borers can’t enter.
To control squash vine borer pupae in soil, you can use a hoe in fall or winter to scratch up the first inch of soil to expose them to predators. You can also apply beneficial nematodes that will kill the pupae. When these microscopic worms are applied to soil, they will seek out the pupae.
The Best Ways to Lower the pH of Soil
While most crops prefer a pH level that is close to neutral, which is 7.0, acid-loving crops such as blueberries require a low pH to thrive. Jeff asks if sulfur — the common soil amendment to acidify soil — is the best product to use to lower pH quickly.
To achieve the 4.0-5.5 soil pH that will make blueberries happy, you can use peat moss — though many gardeners avoid using peat moss due to sustainability concerns. A more sustainable option is finely ground pine bark. In fact, our friend Brie Arthur plants blueberries directly into triple-ground pine park and her blueberries are the prettiest I’ve seen.
But to change the pH fast, the answer is a water-soluble form of sulfur, namely aluminum sulfate.
Carbon Sources for Composting in Summer
Karen K. from my Beginning Gardener Fundamentals course wants to know what she can use as carbon-rich inputs for composting in the summer. Of all the common gardening questions, composting questions are my favorite.
Leaves are my favorite carbon source, but they can be hard to come by before fall. Hay and straw are other great carbon-rich options, so if you practice straw-bale gardening, the old bales can go right in the compost. If you or someone you know raises chickens, you can use the sawdust that is mucked out of the coop. Rabbit bedding is another good option.
Corncobs are something you may have plenty of in summer if you enjoy eating corn. They can be added to a compost pile whole to provide carbon, but can also be broken into smaller pieces for faster results. Stale popcorn, bread, pasta and cereal and nut shells are other examples of food waste that is rich in carbon.
Plain, non-glossy paper is a great source of carbon. It can be added whole or after shredding. Used jute twine and other natural twines can be composted as well.
Why Beans Won’t Grow
Belinda D. in Oklahoma from Beginning Gardener Fundamentals is struggling with green beans. She gets lots of foliage and flowers on her green bean plants, but no beans.
There can be a number of reasons why green beans will not grow, and the first to consider is heat. In temperatures that are consistently 85° and above, especially at nighttime, the plants may not set fruit.
Lack of pollination is another possible reason. Even if you see pollinators in your garden, those bees may be more attracted to your squash flowers than bean flowers.
Soil that is too dry could also be the culprit, especially in high heat, which causes moisture to evaporate quickly. On the other hand, overly moist soil can cause problems as well. For growing beans, keep the soil consistently moist, but not drenched. The soil should be well-draining, which can be achieved by adding compost.
Overfertilizing can also negatively affect bean plants. Too much nitrogen will lead to excessive foliage growth at the expense of bean production.
Sandy B. in zone 9a in Northern California is also struggling with growing green beans — and heat is definitely the problem. Over the last four weeks, temperatures have gotten up to 107°. Sandy is watering two to three times daily while also using a shade roof over her 1,000-square-foot garden. That has kept her tomatoes, cucumbers, eggplant and peppers in production despite the heat. Greenbeans, however, are more sensitive to heat, and simply won’t make it.
When to Use Shade Cloth
A 50% shade cloth can reduce the heat just enough to make a difference in extreme heat. I wouldn’t go up to 60% or 70% shade cloth for mature plants, though, because that will cut down too much on the light that’s needed.
Sara L. asks whether shade cloth is right for her tomatoes in heat over 100°. My answer for Sara is that 50% shade cloth applied during the hottest part of the day — generally when the sun is bearing down from 11 a.m. to 2 p.m. — is the way to go.
Do what you can to moderate temperatures, but don’t make shade cloth a permanent feature of the garden. When it’s unnecessary, take the shade cloth off and let the plants enjoy the light.
How to Overcome Excess Rain
Two Beginning Gardener Fundamentals students have gardening questions on dealing with too much rain. Sandy Y. experienced overwatering, and Nanette M. has had repeated cycles of 5 inches of rain over four days followed by heat waves.
Excessive rain is one of the reasons you often hear me talk about the importance of having well-drained soil. Native soils are usually too heavy and drain poorly, or they are too loose and drain too fast. These common in-ground soil issues are why raised bed gardening makes so much sense: You can control the soil in a raised bed, as well as in containers and in grow bags.
All you can do in a case of overwatering by Mother Nature is focus on creating the most well-draining soil possible. And if you don’t have raised beds, the next best thing is to mound up your in-ground beds. That way, roots won’t sit in waterlogged soil, drown and rot.
When going through cycles of heavy rain followed by extreme heat, as Nanette has experienced, there is an easy way to judge if you need to water the garden, and that is the “finger test.” Stick your finger into the soil. If it comes out clean, the soil is too dry and needs to be watered. If your finger comes up dirty with moist soil clinging on, there is no need to water immediately.
How to Prevent Powdery Mildew
Powdery mildew is rarely fatal, but it is a cosmetic issue and can reduce photosynthesis and respiration in plants. Because this fungal disease likes August weather, “how to control powdery mildew” is one of the most popular gardening questions heard this time of year. There are ways to slow its spread, and you can prevent powdery mildew before it occurs by proactively applying fungicide.
You can make fungicide with milk, sodium bicarbonate (aka baking soda) or potassium bicarbonate, or you can buy a product that contains the active ingredient chlorothalonil or mancozeb. Powderly mildew cannot be “cured” with any of these, but it can be prevented or slowed down.
Always read the instructions on the label of an organic fungicide before applying. If it says it prevents powdery mildew, then that’s the product you want. If the label does not state that it is effective against powdery mildew, don’t assume that it is. Not all organic fungicides are the same.
When using fungicide, it is important to follow all of the directions on the label, starting with diluting the fungicide at the correct ratio. And know that you will need to apply it again if it rains.
For more on powdery mildew prevention, you can read my comprehensive guide on that exact subject.
Using Insecticides & Fungicides in Tandem
Kate H. asks if an insecticide and a fungicide can be mixed together so both can be applied at once, and if not, how much time should she wait between applying one and then the other. She’s also curious which one should be the priority, especially considering that bugs can spread diseases as they feed on plants.
As for mixing two products, I say to always consult with the manufacturers. They will know what can be mixed safely and still be effective. That information is sometimes included on the label, but you can also reach out to the manufacturers directly. Sometimes gardeners are guilty of reading only what they think they need to know before applying, but there is so much more useful and important information on the label to understand. The answers to your gardening questions may be on the label of the product you are holding.
Beneficials, Neutrals and Pest Insects
Jane T. was curious about what bugs are beneficial in raised beds and how to control the bad bugs.
The important thing to realize is that 97% of insects in the garden are beneficial insects or neutral insects. Only 3% or so of insects are considered pests. This is why I always recommend using insecticides sparingly and only after a problem has been identified.
The most renowned beneficial insect is the lady beetle. You can probably picture an adult lady beetle, but did you know the larvae look like little red and black alligators? In the larval stage, lady beetles are voracious eaters of pests such as aphids, mealybugs, spider mites and scale.
The green lacewing is nicknamed the aphid lion because of how effective it is at controlling aphid populations. They also eat caterpillars and beetles.
The syrphid fly, also known as the hoverfly and flower fly, is the name of a number of species of fly in the insect family Syrphidae. They are black and yellow, similar in appearance to a bee, though they only have one set of wings, unlike bees, which have two. Syrphid fly larvae eat aphids, thrips, mealybugs and caterpillars.
The minute pirate bug, also known as the flower bug, is a small oval bug with black and white markings. They are generalist predators that control a variety of insects.
Parasitoid wasps are great to have in the garden, specifically the braconid wasp, which controls tomato hornworm populations. When you see what looks like little grains of rice sticking out of a hornworm, those are the cocoons of braconid wasps.
The damsel bug eats aphids, spider mites, leafhoppers, caterpillars and other pest insects.
The No. 1 organic control for pest insects is beneficial insects, so refrain from using broad-spectrum pesticides that wipe out insects indiscriminately.
The second method is using a physical barrier. Floating row cover over a garden bed keeps insects from getting to leaves to lay their eggs. And then there is manual control: Picking off insects and dropping them into soapy water.
Summer Seed Starting: Indoors vs. Out
Lorinda P. in zone 8a asks what the best place is to start seed for a fall and winter garden. She wants to know if it makes more sense to start the seeds outdoors, since the weather is warm, or is it still better to do it indoors.
The answer comes down to soil temperature. As long as the soil temperature is in the correct range for that variety of seed, you can plant the seed outdoors. If the soil is warmer than the optimal range, start the seed indoors. You can determine the soil temperature in your garden with an inexpensive soil thermometer. Your local university extension service may also report the local soil temperature at various depths.
Cool-season crops need cool temperatures when they are fruiting, but early in their life, when they are in their germination stage and early seedling stage, they can tolerate much warmer temperatures. So don’t be shy about planting cool-season crops now.
That being said, I have trays of kale, Brussels sprouts, beets, collards, spinach and chard in my seed-starting room right now. When your garden is still full of summer crops, it makes sense to start seeds indoors. Indoor seed starting also has the benefit of being free from pest pressure.
Preventing Blossom End Rot
Denise R. is experiencing blossom end rot on a number of her tomatoes, though the majority are doing just fine. The tomatoes never crack when watered, and the soil is amended with chicken manure, bone meal, Epsom salt and ashes. She is looking for a fast-acting calcium supplement to overcome blossom end rot.
Blossom end rot is usually attributed to a calcium deficiency. All tomato growers have this problem sometimes despite doing all the right things. I see it most often in container-grown plants. Most often, blossom end rot comes on because we’re not watering enough. Without water, the roots don’t have the opportunity to get calcium up into the plants.
Epsom salt won’t hurt tomato plants, but it is a myth that it reduces blossom end rot. Another popular myth is that eggshells provide fast-acting calcium. In reality, it takes two years for the calcium in eggshells to become available to plants through the roots. Though eggshells can be pulverized in a food processor or with a mortar and pestle to help them compost down more quickly. You can even just crush them up in your hands to accelerate the decomposition process.
If you get a soil test and find that your soil truly has a calcium deficiency, I recommend gypsum. It is a natural calcium source that can be found in box stores and nurseries. Gypsum won’t affect the soil’s pH the way that lime (another calcium source) does.
The Rule of Thumb for Fertilizing
Cathy H. is looking for a simple(ish) rule of thumb when it comes to fertilizing: How much of what, for which crops and when?
My method to better fertilize plants is to focus on soil health by adding lots of compost and organic matter. Compost is the answer to many gardening questions, from drainage to fertility. The more you amend the soil with compost and organic matter, the less you will need to fertilize. The amended soil will contain more of the nutrients that plants need, and healthy soil has active soil biota that take the root exudates and return nutrients. The more that you can do to create a hospitable environment in your soil to make the soil food web happy, the less work you’ll have to do fertilizing.
When it comes to applying fertilizer, my philosophy is less is more. For the light feeders, light applications will be just right, and the heavy feeders will also benefit. I apply once a month — or every two weeks at the height of summer — with a liquid fish fertilizer, but there are years when I don’t fertilize at all and still have a really productive garden because I focus on building the soil.
I hope you enjoyed hearing these common gardening questions and found the answers enlightening. If you haven’t listened yet, you can do so now by scrolling to the top of the page and clicking the Play icon in the green bar under the page title.
Do you have any burning gardening questions? You can find answers to countless gardening questions on this website, but if you don’t see what you are looking for, let us know in the comments below.
Links & Resources
Some product links in this guide are affiliate links. See full disclosure below.
joegardener Online Gardening Academy™: Popular courses on gardening fundamentals; managing pests, diseases & weeds; seed starting and more.
joegardener Online Gardening Academy Master Pests, Diseases & Weeds: Learn the proactive steps to take to manage pests, diseases and weeds for a more successful garden with a lot less frustration. Just $47 for lifetime access!
joegardener Online Gardening Academy Perfect Soil Recipe Master Class: Learn how to create the perfect soil environment for thriving plants.
joegardener Online Gardening Academy Beginning Gardener Fundamentals: Essential principles to know to create a thriving garden.
joegardener Online Gardening Academy Growing Epic Tomatoes: Tomato expert Craig LeHoullier joins me in leading this course on how to grow healthier, productive tomato plants and how to overcome tomato-growing challenges.
Disclosure: Some product links in this guide are affiliate links, which means we get a commission if you purchase. However, none of the prices of these resources have been increased to compensate us, and compensation is not an influencing factor on their inclusion here. The selection of all items featured in this post and podcast were based solely on merit and in no way influenced by any affiliate or financial incentive, or contractual relationship. At the time of this writing, Joe Lamp’l has professional relationships with the following companies who may have products included in this post and podcast: Rain Bird, Corona Tools, Milorganite, Soil3, Exmark, Greenhouse Megastore, High Mowing Organic Seeds, Territorial Seed Company, Wild Alaskan Seafood Box and TerraThrive. These companies are either Brand Partners of joegardener.com and/or advertise on our website. However, we receive no additional compensation from the sales or promotion of their product through this guide. The inclusion of any products mentioned within this post is entirely independent and exclusive of any relationship.