There are four basic things that all seedlings need: nutrients, moisture, warmth, air, and light. If your seedlings aren’t growing or are growing exceptionally slowly, chances are one or more of these five things aren’t quite right.
Here are nine of the most common causes for slow seedling growth and how to fix them.
Table of Contents
1. The Wrong Soil Structure
Some soils drain well and have a lot of loose particles so that air circulates and allows the roots to breath. Other soils are firm, hold onto moisture, and have poor aeration. If your seedlings are growing slowly, it could be because you’re using the wrong soil structure.
Any good soil has organic matter to provide natural nutrients to the plants, but some soils are wet and some let water drain quickly and become crumbly.
Most people think that all seedlings need loose soil, but that’s not true. Some plants grow faster in clay soils than they will in loamy soils the drain fast with a lot of aeration. Which type of soil is best depends on the plant, so make sure you do your research before you get started planting.
2. Lack of Nutrients
If your seeding started off strong but growth stalled after a week or so, it’s possible that the soil doesn’t have the right type of nutrients. This is especially true if you’re using soil that’s meant for germinating seeds.
When seedlings first sprout leaves, they’re not true leaves. That is, they’re not yet photosynthesizing. The first few leaves are actually a part of the plant embryo, and they’re feeding off of the energy stored in the seeds.
When the first true leaves sprout, the plant shifts to using photosynthesis and nutrients from the soil. At this point, if the soil doesn’t have what the seedling needs, it might struggle. This is the point when you should add fertilizer.
Growing roots need several nutrients, including sulfur, nitrogen, phosphorus, calcium, magnesium, and potassium. Once your babies are feeding from the soil, transplant them into something richer or use the appropriate fertilizer.
3. Not Enough Water
Water is one of the essential things that seedlings and all plants need to grow. Water helps the seedlings transport nutrients from the soil and into the roots and throughout the stem and leaves.
Basically, water keeps the nutrients moving. Without enough water, even the perfect balance of nutrients in the soil won’t do anything for the seedling because it won’t be able to use them.
When a seedling is dry, it experiences cell damage and grows very slowly, and it will eventually dry. Although you may wait for the soil to dry out before watering some other plants, you should always make sure the soil for your seedlings is moist.
4. Too Much Water
As important as it is to make sure your seedlings don’t dry out, you also have to make sure you don’t overwater. In a lot of ways, overwatering is worse than underwatering. Seedlings can bounce back from underwatering, but they are unlikely to do so from overwatering.
The biggest problem that comes from overwatering is root rot. If the roots on your little seedling begin to rot, they will not be able to absorb the nutrients it needs to grow. When watering seedlings, keep the soil moist, but not wet, but watch how much you apply and allow the soil to drain.
5. Warm Compost
Good compost goes a long way and should have a mix of things like grass clipping and peels and waste from fruits and vegetables. Not everyone uses compost, but if you do, make sure that the temperature isn’t too warm.
Because compost is filled with so many bacteria and other microorganisms, it’s usually a little on the hot side. Before using fresh compost on seedlings, make sure you allow it to cool. If it’s too hot, your seedlings will take a long time to germinate and, once they do, they’ll have a hard time growing to their optimal height.
6. Fungal Infections
Fungal infections are quite common, even more so if you overwater. Seedlings are more at risk than mature plants because they’re not yet established and are easier to overwhelm.
Root fungus causes a lot of problems for seedlings, but there are fungal varieties that can damage leaves and branches, too. Research the type of seedling you’re growing and make sure you know what type of fungus it is at risk for getting.
Fungus takes many forms, including:
Blight. Blight is pretty common with tomatoes, so watch out if you have tomato seedlings. It presents as spotting, yellowing, browning, or dying leaves. Increase air circulation, keep the foliage dry, and apply fungicide to treat. Seedlings with blight often never reach their normal height.
Clubroot. This fungus attacks broccoli, cauliflower, radishes, and turnips. It’s tough to identify and treat, but it causes slow growth and is usually fatal for seedlings.
Powdery mildew. This fungus is likely to kill young seedlings. It’s pretty common and takes the form of a white, powdery coating on leaves. Increased air circulation and bottom watering can help treat it. Fungicides are also available.
7. Not Enough Light
Light is one of the most important factors for seedlings. A seedling that doesn’t get enough light will not only grow slowly, it will also be leggy as it’s stretching to get the light it needs.
We know plants need light for photosynthesis, but the light also plays a role in warming up the soil to encourage the seedling to grow. If your seedlings are growing slowly but appear otherwise healthy, use a grow light or another alternative light source until you can transplant them outside.
Insects, most commonly aphids, attack both mature plants and seedlings. Because mature plants are more established, they are more likely to survive an infestation than a seeding.
Aphids are a common pest for seedlings because they are most likely to attack in the spring, which is when most seedlings are just starting to grow. They suck the water and sap from inside of the plant, suffocating the growth by stealing the necessary nutrients.
If you have several seedlings and notice that one is growing much more slowly than the others, there’s a good chance that the plant has an aphid problem. Depending on how bad it is, the plant is unlikely to survive.
In that case, remove the infested plant and ensure that the others do not suffer the same fate. You can remove the aphids manually, or use neem oil to kill them.
9. Too Much Competition
If you plant too many seedlings too close together, they will eventually begin competing for nutrients from the soil. This is a pretty natural occurrence, and some people use it as a way of determining which plants are the strongest.
Sometimes, seedlings that aren’t growing as quickly as their neighbors are discarded since they are seen as weaker. Alternatively, you can transplant them to a new area if needed. Here is a general outline of this delicate process:
1. Prepare the seedling’s new home. You can use the same type of container as you’re using for your other seedlings or use a small starter pot.
2. Fill the new pot with nutrient-rich soil and dig a small hole to accommodate the seedling and its roots.
3. Gently move the seedling from the old soil into the new pot and cover the roots with the same nutrient-rich soil.
4. Water generously.
5. Monitor carefully.
The best thing to do is avoid the problem in the first place is plant them separately in the first place. This is precisely why you see a lot of starter kits with individual holes for each plant.
As you can see, there are many reasons why your seedlings might be growing slowly. If you notice a fungal infection or bug infestation, treat it as soon as you can to see if the seedling bounces back.
If there is no obvious fungal growth or bug problem, the best thing to do is ensure that they have enough nutrients, moisture, warmth, air, and light. Remember, seedlings are vulnerable and delicate, and a lot of things can affect their growth. Make sure they have what they need and monitor closely to see if additional changes are needed.