Everything to Know About Squash Seedlings - A Complete Guide

Growing squash from seed is one of the most rewarding garden tasks out there. Whether you’re growing prolific summer squash or massive winter squash, you’re sure to see results. Squash seedlings are easy to start but can be somewhat delicate. The best way to take care of them well is to understand their early stages so that you can reap a successful harvest. 

The Anatomy of Squash Seedlings

Like most vegetable seedlings, squashes are dicots, meaning they have two cotyledons. Cotyledons are the “seed leafs.” They are what exists inside the seed and pop out first upon germination. These leaves are photosynthetic and help get the plant started until it’s strong enough to produce its first “true leaves.” 

Germination Process Explained

The seed is the embryonic stage of the plant life cycle. Squash seeds, like most seeds, contain three main parts: the embryo, the endosperm, and the seed coat. The embryo is the fertilized part of the seed, or the part that actually becomes a plant. The endosperm is made up of starches, oils, and proteins and is what feeds the embryo once it sprouts, but before it’s able to take up nutrients from the environment. The seed coat is the protective outer layer of the seed. 

When a squash seed comes into contact with moisture, the seed will start to take up water through the seed coat. It will then swell, which breaks the seed coat open from the inside. The embryo, made up of a small shoot and small root, will emerge root first, anchoring the seed to the soil. Then the shoot will emerge and you’ll see the cotyledons. 

Factors Affecting Squash Seedling Growth

Squash can either be directly sown at the right time of year outdoors or started inside and transplanted once the weather is agreeable. In either case, squash seeds need the right environmental conditions in order to germinate. 

Temperature

Squash, both winter and summer, is a warm season crop. Seeds can be directly sown into the garden after all danger of frost has passed or started indoors three to four weeks before your last frost date to be transplanted out. 

Squash seeds germinate best when soil temperatures are between 70 and 95 degrees fahrenheit. This means, when starting them indoors, you’ll most likely want to use a heat mat to ensure warm soils. 

Planting Medium

While any seedling mix will do the trick when starting seeds indoors, squash will not tolerate poor soil quality once transplanted out or directly sown. You’ll want a nutrient-rich soil to ensure those heavy yields that squash is known for. Consider fertilizing your plants regularly or mixing in plenty of compost and a slow release fertilizer into the soil ahead of planting. 

Light Requirements

A lack of sunlight could inhibit your seedling development when starting indoors. Consider setting up grow lights so that your seedlings can get the light they need. When direct seeding squash seeds you’ll want to consider sunlight as well. Squash will grow best in full sun, so take that into consideration when giving them their permanent summer home. 

Water Needs

As explained above, water plays a huge role in germination. You must provide enough water for the seed to swell and burst the seed coat. In fact, improper watering is the number one reason gardeners have poor germination rates. 

Common Challenges and Solutions

There are a number of issues you can run into with squash seedlings, but they’re easy enough to avoid with understanding and a few preventative measures. 

Damping Off

Damping off is a fungal issue that can be exacerbated by certain environmental factors. The fungus can cause seeds to decay without germination or affect seedlings. Typically the stem at the soil surface will turn brown and the seedling will fall over, killing it. 

Once damping off begins, there is no turning it around, however there are some steps you can take to mitigate the effects of this fungus or stop it entirely! Damping off is exacerbated by cold, wet conditions. This means that overwatering coupled with a lack of a heat mat can make things worse. Airflow can also affect damping off. We recommend keeping a fan running in the room where your seedlings are growing. Keeping air moving around the room can help to mitigate all fungal issues! 

Leggy Seedlings

“Legginess,” as we call it, refers to a seedling with an oddly long stem. Often leggy seedlings will be leaning one way as if reaching for something, and this something is most often a light source. If you notice your seedlings getting leggy, you’ll want to give them more light by either moving your existing grow lights closer to the plants or giving them more time outside in the sun (while watching for cold weather, of course). 

Nutrient Deficiencies

There are any number of nutrient deficiencies that could be affecting your squash seedlings. If you are growing your seedlings in a high quality, nutrient-dense seedling planting mix, you should not run into any issues with this. If you’re growing them in low quality potting soil or something similar, you will likely find that your seedlings may “fail to thrive.” They may get to a certain height and stop growing entirely. The best way to tackle this is to ensure that you’re planting in a high quality mix — something that is dense in nutrients and micronutrients, but not too high in nitrogen, which can burn seedlings. You can find high quality soil mixes at your local nurseries, hardware stores, or even make one yourself! 

Overwatering

Too much water fills in all the air pockets in the soil, which robs the roots of oxygen that’s needed for proper root growth and development. You may see molding on the surface of the soil or on the plants themselves. This can also result in a failure to thrive and limit development significantly. We recommend adequately moistening your soil at planting time — to the point that when you squeeze a ball of it in your hand, the soil holds its shape, but doesn’t squeeze out water — and then misting the surface of your soil twice a day or watering from below. Remember, overwatering can also exacerbate damping off, so keep an eye on that soil temperature and airflow as well. 

Underwatering

Unsurprisingly, underwatering can also cause problems. Insufficient watering can cause the leaves to turn yellow and eventually drop. You’ll see the leaves wilting as well. 

Preventing Pests

As discussed earlier, damping off is an incredibly common seedlings issue, but there are other things to watch out for as your squash seedlings are developing! Pest infestations can cause major problems before you’re able to harvest. 

Aphids

Aphids can be a common problem for seedlings, particularly if you put your homegrown seedlings near ones you purchased from a nursery without quarantining them first. If aphids infect your seedlings, gently clean them off with a damp cloth. Make sure you’re getting as many as you can or perhaps check and wipe them daily. If your infestation is really severe, you can always apply neem oil which should take care of the problem. 

Squash Bugs

Squash bugs are likely to be found on your seedlings in the garden if you’ve direct seeded or after you’ve transplanted. This is particularly true if you’re succession planting and growing squash later in the season. While squash bugs aren’t actually all that harmful to an established plant, they can wreak havoc on young squash seedlings. Try to catch them early, killing the rust colored eggs. If the population has matured you can also remove them by hand and drop them in a bucket of soapy water. 

Squash Vine Borer

Squash vine borers can be a problem for squash plants of all ages but are especially harmful if they attack your plants early. They do exactly what the name indicates. They bore into the stem of the plant, usually close to soil level, and feed through the center of the stems, hollowing them out and blocking the flow of water from the roots to the rest of the plant. This can quickly decimate an entire crop. Prevention is the best tool! The moths that lay the eggs at the stems of your plant are attracted to yellow. Some growers use yellow sticky traps and others use yellow bowls filled with soap and water to trap them, which can stop them from laying their eggs. Further, a physical barrier will help as well. Consider using row cover, before your seedlings are flowering, so that eggs cannot be laid. And if your squash seedlings do get attacked, there are still steps you can take. Monitor your plants closely for signs of wilting or boring. If you notice issues, take a clean sharp knife and cut a slit into the affected stem. Slice carefully until you find the borers and remove or kill them. Once you’ve done this, pack moist soil around the cut area and keep it watered well. More roots may sprout at the sight and you might be able to save the affected plant!

Transplanting Squash Seedlings

Like other cucurbits, squash seedlings can be prone to transplant shock. This doesn’t mean it’s explicitly not recommended or can’t be done, but it’s something to consider when deciding what seeds to start indoors and what to direct seed. 

Ensuring a Successful Transplant

Squash seedlings can be transplanted after all danger of frost has passed. The reason they are so prone to transplant shock is because their shallow roots are very sensitive to disturbance. If starting your seeds indoors, we recommend planting them in four inch pots. This will give them plenty of room to grow and give you plenty of soil to handle during transplant time to limit damage to the root systems. You don’t want to be potting up your seedlings as they grow, and you’ll want to be moving them only once — into the garden once they’re mature enough. 

When transplanting, be very gentle, try not to make the root system move around too much, and plant the whole cell of soil in the ground. Mound your garden soil just a touch around the stem at soil level to ensure they are securely in the ground.

Just like when inside, ventilation plays a vital role in the garden when preventing fungal diseases such as downy or powdery mildew. Ensure you’re planting your squash seedlings an appropriate distance from each other, two to four feet, depending on the squash. This allows for airflow and for leaves to fully dry out after a cool, wet night or heavy watering. This is step one for making sure fungal issues don’t thrive.  

Caring for Squash Seedlings After Transplant 

Your newly transplanted squash seedlings will want plenty of water while they’re getting established in the garden. Typically, vegetables are looking for one inch of water a week. If it’s raining fairly consistently you should be fine, but if not you’ll want to water once a day. Plant stress due to underwatering can affect the long term health of your crop. 

Luckily for us, once transplanted, and barring any severe nutrient deficiencies, pests, or diseases, squash tend to thrive well on their own! Once your plants are established in the garden you should be able to let them do their thing and enjoy the magic. 

Ensuring Your Squash Seedlings Thrive in Your Garden 

The first step to ensuring high quality harvests is to start with high quality seeds. You can grow all kinds of squash in your home garden. 

Winter Squash

Delicata Bush

Delicata is a beloved winter squash that is heralded by gourmands everywhere. This bush-habit variety has a tidier growing pattern, with vines extending up to about five feet instead of around ten, with a nutty flavor and creamy skin. They make great keepers, too. 

North Georgia Candy Roaster

Forget the pumpkin pie! Grow this Appalachian heirloom for pies, breads, soups — the opportunities are endless! Candy Roasters are well known in the mountains for their full flavor and many uses. This particular variety has an elongated banana shape with a pink-orange rind and grows about 18 inches long.

Tahitian Butternut

This variety is sweeter than most other squashes and gets better with age! These large fruits are shaped like butternuts with elongated necks and a light, golden orange skin. They get sweeter the longer they store for. These vigorous vines show some mildew resistance and love a long, warm growing season. Like other butternuts, they tend to be resistant to squash vine borers. 

Summer Squash

Cocozelle Zucchini

This heirloom summer squash features slender fruits with light and dark green stripes on smooth, thin skins. It has an outstanding flavor and a dense flesh. Harvest when they’re less than ten inches long.

Early Prolific Straight Neck

The name says it all! Early producer and prolific numbers of squash with straight necks. What more could you want? This is the most popular of the straight neck squashes and has lemon yellow skin with a crisp, firm texture. These are best when harvested at five to six inches long.

Tromboncino

These summer squashes grow loooooong necks which curl in fanciful shapes. The fruits are tastiest when harvested and eight to 18 inches long and have a slightly sweet flavor. Because this summer squash is a different species than most others, it shows resistance to common summer squash pests such as vine borers as well as diseases like powdery mildew. 

Gourds

Luffa

Luffa plants have so much more to offer than just bath sponges! Grow them for their ornamental, carefree, rampantly exuberant vines which produce lovely two inch flowers in the summer heat. The young, tender fruits are often used in Asian cuisines, as they are a tasty vegetable when lightly steamed or stir-fried. On the fully mature fruits, peel the skin back to reveal the sponge-like material. 

Tennessee Spinning Top

Toys DO grow on trees! Well, vines. This small, two to five inch, bottle-shaped gourd has a gorgeous green striping. The dried gourds are great for ornamental and craft use and make great spinning tops for kids! 

Birdhouse Bottle

Want another craft? Bottle gourds, als known as birdhouse gourds or calabash, are known for their rounded shape, which makes them perfect for making containers, large scoops, musical instruments, and of course, whimsical birdhouses. 

Regardless of what you choose to grow, with this information on hand you’re sure to have an absolutely stunning harvest!

	Article Written by: Hannah Gibbons
	About the Author: Hannah Gibbons, an employee at Sow True Seed since 2020, has nearly a decade of experience in the agricultural industry. Their passion for environmental education and regenerative agriculture has been the cornerstone of their work, aimed at making gardening accessible to all.