Squash: What Can Go Wrong and How to Prevent It

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Are you growing summer squash? Most home gardeners grow some kind of squash in their summer garden. However, growing squash isn’t without its troubles. I like to call this a “feast or famine” crop — because when everything goes right, a bumper crop awaits! But this isn’t always the case, even from season to season.

You may have the most abundant harvest one year and completely go without the next (ask me how I know). If you’re hoping for that bumper crop this year, let’s look at what could go wrong so we can avoid some of the common issues that arise. We break this down in full detail on The Beginner’s Garden Podcast. You can listen to that here or keep reading.

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Planting Squash

Planting from seeds indoors too soon

If you’re a long-time follower, you know that for years I always direct sowed my squash seeds into the garden with no transplanting necessary. I still recommend it as an easy way to grow squash. But the truth is, I couldn’t get my squash to grow well from seeds indoors so I gave up for several years.

I have since learned that the problem with starting squash seeds indoors is that it’s not super forgiving when it comes to transplanting. Squash plants don’t like their root systems disturbed. However, it’s not impossible to transplant. The key is getting your transplants out into your garden before they get too large.

If you plant your seeds indoors, I recommend planting them 2-3 weeks MAX before you plan on transplanting them into the garden. If your plant develops more than four true leaves while still in its container (don’t count the “seed leaves”) then it likely will not transplant well. The plants have a high likelihood of stunting and may suffer the rest of the season.

When I transplanted my squash and zucchini with only four true leaves, they took to the transplant well and flourished.

Planting in the garden too soon

While we don’t want to wait too long to transplant our squash seeds from indoors, we also don’t want to transplant them into our garden too soon. Make sure you keep an eye on the weather and don’t plant during the cold.

Ideally, nighttime temperatures should remain steady in the 50s or higher before planting, and in the case of a late cold snap, be sure to cover them if a late frost or freeze threatens.

However, keep in mind that squash is a summer crop and there’s not a guarantee that covering them during a cold snap will fully protect them. I’ve lost squash transplants to freezing temperatures even when covered.

The way to avoid planting to soon in the garden without letting the squash outgrow their containers if you start seeds indoors is to wait longer to sow the seeds indoors in the first place. Don’t start indoors until two weeks before your average last frost date; waiting a week or two is even better in many cases.

Not hardening off appropriately

Hardening off your seedlings means that you are gradually introducing your plants to natural elements such as the cold, the wind, the rain, and perhaps more important, the sun.

We may not think about acclimating our plants to the sun, but sunburn can occur if we take them outside too long in the beginning. I took my plants to the greenhouse a little too early this season and they did develop some sunburn on their leaves.

Sunburn squash leave
sunburn on squash leaves
sunburn on squash leaves

This was a mild case and wasn’t detrimental to my plants, thankfully. They grew new, healthy leaves and the sunburnt one eventually dropped off. But more damage could have severely stunted or even killed the plant.

Direct sowing too early

Squash is very easy to direct sow in your garden, so don’t feel like you have to try indoor sowing and transplanting. To direct sow squash successfully in the garden, keep in mind that, again, squash is a summer crop. The weather — and more importantly, the soil temperature — matters with this plant. The minimum temperature your soil should be before direct sowing squash is 60 degrees, however, the optimal temp for germination is 85-95 degrees!

Because of this drastic temperature difference, I wouldn’t plant mine until the soil is much warmer than 60 degrees. It can take longer to germinate and you risk that seed rotting in the soil the cooler your soil temperature is.

Planting too close together

I see this mistake most often with container planting. People try and plant 3-4 seeds per pot. If you aren’t familiar, squash plants can grow HUGE. They are also heavy feeders, which means they hog all the nutrients in the soil they can find. Because of this, each plant will compete with one another for the nutrients they need if they are planted too close together. What that means is that both (or all) plants will suffer — yielding less than one healthy plant without competition.

Ideally, squash is best planted two to four feet apart. This is so hard to do if you’ve never seen squash fully grown. My raised bed squash expanded over 6 feet one year! So, if you are planting in a pot, stick with one seed/plant.

massive squash plant
Squash and zucchini can get huge, so don’t plant too close!

Growing Squash

Now that we’ve talked about mistakes to avoid in planting squash or zucchini, let’s explore mistakes to avoid in growing it.

Not growing in fertile soil

If you’ve ever seen a random plant growing out of a compost pile, there’s a good chance it’s squash (or pumpkin, or another relative). All cucurbits, but especially squash, love compost! The more you can add to your container or raised bed, the better. If your squash isn’t growing well, there’s a chance it’s not taking in enough nutrients. Compost is the best ingredient you can add to a squash or zucchini planting for maximum fertility.

Planting in poor draining soil

While most crops need well-draining soil, squash and zucchini are a little more temperamental about this. If you live in an area that has clay soil or just doesn’t drain well, consider growing your squash plants in raised beds, containers, or by creating a hill of compost in which to plant.

Not enough water

Conversely, squash also needs plenty of water. Squash plants are shallow-rooted. This means that the main part of their root system is going to be only about 6 inches down into your soil. So it’s a good idea to water often and mulch your squash to help retain that water moisture level. (Mulch helps alleviate excess moisture, too!)

Lack of pollination

If you aren’t familiar with squash, they require bees for pollination. There is a male flower and a female flower that form on your squash plants. The female flowers will have what appears to be a baby squash starting to grow at the base. The male flowers have no fruit at the base, but instead, a cone shape growing out of the middle of the flower that is coated in pollen.

Squash plants require bees to take the pollen from the male flower to the female flower in order to produce the fruit. Ideally, nature takes its course on this one, but sometimes, there aren’t bees to make it happen. These flowers open up very early in the morning and this is when the pollination happens.

If the bees haven’t figured out where your squash plants are yet, or if there is a rainy morning, pollination may not happen. And because female flowers only open once, one time per day, the window is slim.

female squash flower and squash on plant

Most beginning gardeners don’t realize this. They notice a little baby fruit (on the female flower) for several days, not growing. Later, this baby fruit shrivels up. If you walk out into your garden from one day to the next and you don’t see considerable growth on this baby fruit, there’s a good chance it wasn’t pollinated.

What can you do to help? Well, you can play cupid. Take your male flower, pull the leaves off and rub the pollen on your female flowers every morning. This is tedious and not fun after the first few times, but if you want squash, it’s sometimes necessary for the short term.

In the long term, try and plant some pollinator plants that are native to your area and attract bumblebees, squash bees, and other native bees. Basil and sunflowers are great at attracting these bees, but they are usually not in flower for the early spring harvest. Instead, let your spring brassicas go to flower, or plan ahead and plant a flowering cover crop like crimson clover.

crimson clover attracts honeybee
Crimson clover, planted in the fall, blooms early and attracts early pollinators in the spring.

Nasturtiums are also great at attracting bees, and they are a great squash companion plant!

nasturtium as companion plant for squash
Nasturtium flowers attract bees needed for pollinating squash and zucchini.

Waiting too long to harvest

If you’ve grown squash, you know they can go from unseen to too ripe almost overnight, right?! The best time to harvest a squash plant that tends to grow longer squash fruit is when it reaches 6 to 8 inches in length. If it’s a patty pan type, 3 to 4 inches is preferable, and for a crookneck, you want to harvest the fruit at about 4 to 7 inches.

large zucchini squash

In general, there’s not really such a thing as too early for picking. The smaller they are, the more tender. Usually, the ideal time for picking them is just a few days after they pollinate! That’s how fast these grow. AND, the more you pick your squash, the more it produces.

If you accidentally miss one, what then? Well, if it’s too tough (where your fingernail won’t dent the skin), throw it to your chickens or in your compost pile. If it’s too big to eat fresh but not quite bad enough to discard, shred it for zucchini bread.

Blossom end rot

Most people associate Blossom End Rot with tomatoes, but our squash friends can suffer from this as well. The end of your squash starts to get soft and brown. It’s easy to mistake this for squash that wasn’t pollinated, but you can usually see a rotting spot on the blossom end that doesn’t extend to the rest of the fruit.

Blossom end rot happens because the plant isn’t getting enough calcium from the soil taken to the plant. But usually, this isn’t due to a calcium deficiency in the soil. Instead, it’s more likely that watering (or rainfall) has been irregular. To prevent blossom end rot in squash, make sure you are consistent with watering your plants. This is especially important if you grow in containers, where the soil can dry out quickly.

Insects and Pests

Just when you thought we had already discussed everything that can go wrong with squash, we have to talk about pests — because squash pests may be the number one problem for many gardeners. Let’s look at the bad actors around our prized squash and zucchini plants.

Squash Vine Borer

The squash vine borer is a black moth with a red dot on the top. It lays its eggs at the base of the plants. Those eggs hatch out and form a larva that tunnels into your plant’s vine. They eat the plant from the inside out. This restricts the flow of nutrients to the plant from the soil and vice versa.

Squash vine borer egg
The squash vine borer’s egg is so small that you might mistake it for dirt.

If you’re not familiar with the borer, you’ll notice its destruction first. You may go outside one day and find your squash or zucchini plants wilted. You may assume this is a lack of water or extreme temperatures.

The real problem here is that once you actually know your plant is infected from squash vine borers, it’s too late to help your plant. If you look at the base of the soil where your plant grows out of and see sawdust material, it’s safe to say you’ve got this grub.

Squash Vine Borer
Look closely at this vine that I cut open, and you’ll see the black-headed squash vine borer grub.

Your options from there are to do surgery and fish that grub out of the plant (not at all fun). This is labor-intensive if you have many plants but doable if you only have a few. If you choose to go this route, bury the damaged stem in soil and water well. There’s a chance the plant can be saved, but in my experience, the yield after such a trauma to the plant is miniscule. Still, here’s a video that will show you how to do it:

Over the years, I’ve pretty much given up on the squash vine surgery. Instead, I’ve shifted to a more hands-off method:

I observe when the moth will be present in my area and I plan my squash plantings around it. I know that my spring crop will eventually succumb, and I plant a second harvest later to try to get a late squash harvest after the moth has finished its life cycle. This cycle will differ from region to region, so observe when your plants are most affected and adjust.

Squash Bug

Squash bugs are a pain, but compared to the vine borer, they aren’t as deadly and are easier to manage. If you see squash bugs mating on your plants, check the undersides of your squash leaves for copper-colored egg clusters. Get rid of these at once. I like to scrape them off, and some gardeners use duct tape to dislodge them without damaging the leaves.

Squash Bug eggs

Searching out and killing these eggs is an everyday task from the time you first discover the insects. If you miss these and they hatch, you can still kill the gray nymphs relatively easily with organic options aimed at soft-bodied insects, but once these get to the beetle stage, they are nearly impossible to eliminate. If this gets out of control, it’s best to pull the plant out and throw it away.

Squash Bugs
Squash bug nymphs can be controlled with insecticidal soap, but catch them before they develop into adults.

Cucumber and Flea Beetles

While I haven’t had any major issues with the cucumber beetle in my own garden, it still can pose a threat. They can attack seedlings and do considerable damage, but perhaps more concerning, they can carry bacterial wilt. Like other beetles, these are difficult to control organically. Covering the plant before flowering begins may be the best prevention. This way, the plant can have a chance to grow strong before uncovering and can better withstand the pest.

I also don’t have issues with flea beetles affecting my squash, because they are typically hanging out on my potatoes or radishes. But, if you know these are a problem for you, cover the crop early on until flowering begins and they need the bees. (Covering them after you notice the flea beetles is too late.)

Pickle Worm

This is something I have no experience with and for that, I’m thankful. This is one tough insect to deal with! The pickle worm lays eggs inside the flower of squash plants and damages the flower and the fruit. Because these larva and worms affect the actual flowers, it can be deadly to beneficial insects (like bees) to spray insecticides.

Protecting bees is a priority for me, and if you feel the same, I recommend treating these much the same as I do the squash vine borer and plant your crop around their growing cycle.

Squash Diseases

Finally, we come to squash diseases. These can cripple your crop so it’s good to know what to look out for.

Powdery Mildew

The most common disease I’ve faced with squash is powdery mildew. This is most common in the fall when the weather is humid and a bit cooler at night. Prevention measures go a long way, and organic controls help if you start treatment early. I am also currently testing varieties of squash that are supposed to be more resistant.

powdery mildew on squash

Bacterial Wilt

If you see your plant wilting, first check the base to make sure it’s not the squash vine borer. If you rule that out, and you determine your plants are infected with bacterial wilt, sadly, there’s nothing you can do. Pull the plant and destroy it (don’t put it in the compost pile). Most likely, the culprit was an insect such as the cucumber beetle, so for the next planting, research control methods for the beetle.

Blossom Blight

If you see a black, whiskery growth happening on your squash fruit, you may be dealing with blossom blight. I actually had this in my garden and didn’t know that it was blight. I assumed it was a lack of pollination and my plants were rotting from that. This is typically found in rainier times of year because it thrives in humid areas. To prevent further issues, try and open up the area around the plant, increasing the airflow. This may mean pruning a bit or for the next planting, spacing out your plants nore. The good news is this usually corrects itself in the warmer, drier weather.

Viruses

As if we haven’t given you enough problems, we throw the possibility of a virus. Last year in my garden my squash started to grow green-looking warts on them.

mosaic virus on zucchini or squash
Mosaic virus in squash and zucchini can present as ugly warts on the fruit.

It turns out that my plants were affected by the Mosaic Virus. Mottled leaves, twisted or curled leaves, and green-looking warts on the fruit are all symptoms of this virus. This is also most common in late plantings and transferred through leaf hoppers. Sadly, once affected there’s nothing that can be done. In my experience, the mosaic virus didn’t kill the plant, but yield was severely stunted. The fruit, though they look ugly, are perfectly fine to eat.

While we gave you so many things that can go wrong, please remember that squash is still capable of producing more than you can eat! Chances are you won’t have all of the issues discussed here when dealing with your squash plants. But even if a few apply to you, hopefully this guide has helped you know how to identify the squash problems and how to deal with them.

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One Comment

  1. Hi !!
    I’m sorry you lost your cousin.
    Enjoyed your blog on the squash vines.
    I’m in south western Oregon. 50 miles inland from the coast.
    I have started Luffa seeds and am going to try to grow them.
    Have you ever grown them and do you have any advice?

    Thank you,

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