7 Tips for Preventing Spindly Vegetable Seedlings
Leggy, spindly seedlings are heartbreaking to see. You planted seeds hoping to grow strong, healthy plants and now have to deal with elongated weak ones! Fear not, as some simple tricks turn these leggy specimens into robust seedlings. Seasoned grower Jerad Bryant shares these seven expert tips for preventing spindly veggie starts.
Contents
Plants reach for the light mainly because they need it to survive. As seeds germinate and plants emerge, they use their first leaves, called cotyledons, to sense where the light is and how strong it is. If it’s far away, the seedlings reach up high to get as close as they can to the source.
Though other factors also influence spindliness, light is the most important factor. Proper brightness will give your crops a healthy start and ensure they’re ready for transplanting outdoors in no time! Without it, you’ll have to do some transplanting, cutting back, and moving around to ensure proper plant growth.
Other conditions also influence how tall plants grow; temperature, airflow, and humidity affect plant growth. Let’s see how to control these factors for healthy, strong baby plants no matter the season. These seven tips will help you prevent spindly seedlings, whether you’re starting them indoors or outdoors.
Ensure There’s Enough Light
All plants naturally reach toward light thanks to a scientific phenomenon called phototropism. Bright light is especially crucial for young vegetables! They need plenty to sprout new stems, leaves, and buds. Without it, they’ll reach towards the brightest source—in especially dark rooms, you can see them extend towards incandescent or fluorescent bulbs!
By ensuring proper brightness levels at germination, you’ll avoid leggy issues after sprouting. How close to situate plants near light sources depends on the type; direct sunlight, grow lights, and filtered light affect young plants differently.
I like to use grow lights to start seeds because they’re reliable and you can set them up on timers. Rather than hoping for bright, natural sunlight, you can have a grow light setup that reliably sprouts healthy vegetables.
How close your lights should be to your vegetables depends on the type you’re using. Fluorescent bulbs should be close to germinating plants, within two to three inches of their tops. LED lights are typically brighter and stronger than fluorescent types, and can sit six inches or more away from the plants’ tops.
Without grow lights, set up seedlings next to a cool window with plenty of natural sunlight. Filtered light works okay, though some direct sunlight helps develop full sun-loving crops like tomatoes, eggplants, and peppers.
Moderate the Temperature
Temperature, like light, influences how vegetables adapt and change. Some, like lettuce, respond to temperature shifts by bolting. Increasing temperatures tell them that summer is approaching and it’s time to flower and form seeds. Prevent bolting and other undesirable growth changes by keeping your vegetables in their preferred temperature range.
Most crops, including lettuce, endive, and onions, prefer cool ranges while they mature. Hot temperatures cause rapid, weak growth, leading to unhealthy transplants later in the growing season. Our indoor rooms are often too warm for them—it’s best to sprout seeds away from heater drafts. A cool window or unheated room are good locations for germinating seeds.
Other hot-loving species excel while temperatures are warm. Peppers, eggplants, and tomatoes are three main species that prefer high ranges to grow well indoors. Though they like warmth, they perform poorly when temperatures rise above 85°F (29°C).
Remove the Heat Mat
Heat mats are excellent tools for boosting the temperature. They warm the soil, creating optimal conditions for seed sprouting. When you use a heat mat with a humidity dome, you create the ideal conditions for germinating warm-loving species indoors.
After germination, you can safely remove the heat mats to prevent unruly, spindly growth from your seedlings. The high temperatures, though beneficial for sprouting, lead to spindly vegetables under low light levels. You want them to mature slowly so they don’t outgrow your space. Otherwise, you’ll have to prune the veggies back or repot them while you wait for the last average spring frost date.
Never use heat mats to sprout seeds that germinate at low temperatures. The heat prevents them from sprouting, and, if they do germinate, they’ll bolt or grow abnormally. Only use heat mats to sprout tropical and heat-loving crops, and remove them after germination.
Take Off Humidity Domes
Like heat mats, humidity domes are excellent for creating ideal seed sprouting conditions. However, after sprouting, leaving them on is less than desirable! The domes filter sunlight, leading to lower levels that can cause spindliness. This is especially troublesome in areas with fluorescent or filtered lighting.
After seedlings emerge, you can safely remove the humidity domes to prevent spindly growth. Excess humidity is excellent for seed sprouting, but it can cause mushy leaves or root rot in maturing seedlings.
The only time you’ll want to leave the domes on is when you’re starting plants outdoors. The domes protect maturing seedlings from harsh frosts in late winter and early spring, preserving warm air near their leaves and stems. Open the domes once a day for airflow, and safely remove them after outdoor temperatures warm to the veggies’ preferred ranges.
Add Airflow
One way to look at indoor seed starting is this: it’s a replication of nature! Nature has wind, water, and sunlight. Without airflow, seedlings develop weak, spindly, and leggy shoots. Though airflow may seem damaging to tender plants, it creates the right environment for them to grow strong and dense.
Fans are unnecessary outdoors because natural wind flow is present. Indoors, a fan simulates the wind to create strong plants. As the wind blows on your vegetables, their stems and roots must thicken and grow more shoots to combat the air’s pressure. Just as trees grow strong where winds are constant, seedlings develop thick and robust growth where airflow is present.
It’s best to situate strong fans near your propagation station rather than directly on it. Strong winds can cause the leaves to dry out quickly, leading to thirsty, withering veggies. If you don’t have fans, simply blow on your crops one or more times a day. Your breath simulates natural wind, and it also gives your plants plenty of carbon dioxide in the process!
Transplant Leggy Seedlings
The five tips above help prevent spindly young crops, though what happens if your seedlings are already leggy? The best way to promote dense, healthy growth in the future is to transplant them while they’re young.
Young shoots grow roots from their stems easier than mature ones; burying the leggy veggies and increasing light levels causes them to grow squat, dense, and robust in the future.
Start by removing the tender seedlings from the soil. Gently lift them by their cotyledon leaves, the first one or two leaves that emerge. Use extra care so as not to damage the young roots, leaves, or stems.
Gently place the tender sprouts into new containers with fresh potting soil. Place them so the leggy stems are under the soil—new roots will grow from the underground stems, and leafy growth will sprout from above the soil. Water them well, then place them under bright light for most of the day.
Cut Back Mature Seedlings
Cutting them back can prevent spindly seedlings and encourage bushiness, slower growth, and dense foliage. This option works well for mature seedlings that have progressed past the point of transplanting. I often cut back peppers, tomatoes, and onions if they grow too tall indoors.
Cutting back plants creates wounds from which new growth sprouts out. Species like tomatoes or peppers sprout two new stems from a single cut, leading to the bushy, dense foliage we desire. Though this is desirable, the crops require energy, time, and sugars to form new shoots. Avoid cutting back your veggies if you have a short growing season, as they may not have enough time to recover.
This method works well on bushy, shrubby plants with hardy stems. Though cutting back works well for mature plants, it’s not ideal for young seedlings. They may die if you chop them back; they lack sufficient energy to produce new growth. Use the transplanting method instead, or move them under bright light and cut them back when they’re older.
