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How to Care for Plant Seedlings

The Spruce / Margot Cavin

When you start seeds indoors, the tender seedlings are dependent on you for all their needs.   This includes getting fed. Some gardeners think their seedlings will grow faster if they give them fertilizer right away. However, while those tiny plants may look helpless, they don’t need anything other than water, warmth, and light for their first few weeks. They are capable of feeding themselves up to a point. After that, it’s time to start feeding them, following a few standard guidelines.

When to Start Fertilizing Seedlings

When seedlings first poke out of the ground, they are still feeding off the food stored in the seed.   The first couple of leaves that form are not leaves at all. They are called cotyledons or seed leaves, which are part of the seed or embryo of the plant. Cotyledons contain the remainder of the stored food reserves of the seed, and they keep the seedling fed until the first true leaves sprout and the plant can begin photosynthesis.

Usually, the cotyledons disappear shortly after the first true leaves form and begin photosynthesizing. It is at this point that the seedling can use a little boost of fertilizer.

Before you reach for the plant food, make sure you haven’t used a potting mix that already contains fertilizer. Some do, and some don’t. If the mix has fertilizer, you shouldn’t need to add more. For the future, because seedlings can initially feed themselves, you don’t need to use a potting mix with fertilizer for starting seed. Using a mix without fertilizer is cheaper, and more importantly, you can control how much and what type of food your seedlings get.

Selecting Fertilizer

Seedlings tend to need a fertilizer that’s high in phosphorous. Phosphorus stimulates root development and is a component of photosynthesis. Look for a 1-2-1 N-P-K (nitrogen-phosphorus-potassium) ratio on the fertilizer label. A liquid or water-soluble fertilizer is typically the easiest and quickest way for the seedlings to access nutrients. You’ll also have a choice between organic and synthetic fertilizer, which often comes down to personal preference.

  • Synthetic fertilizer: If you are using synthetic fertilizer, feed your seedlings weekly. However, it’s often wise to dilute the label’s recommendation by at least half. Tender seedlings can be easily burned by too much fertilizer. Young seedlings commonly can get away with a quarter of what the label recommends for full-grown plants.
  • Organic fertilizer: There are several liquid organic fertilizers available, though they sometimes can be hard to locate. A mix of fish emulsion and kelp can also give your seedlings the nutrients they need to get started and reduces the risk of burning your seedlings. As with synthetic fertilizer, give your seedlings a dose of organic food weekly. Unless the product is labeled specifically for seedlings, dilute it by at least half the recommended dose. It’s better to give your seedlings a little food regularly than to risk burning those tender roots with too much fertilizer at once.
  • Another option: Mix a granular organic fertilizer into the potting soil. Many gardeners do this when their seedlings are ready to be moved from their starter containers to larger pots. However, granular fertilizer can take a while to release nutrients and impact the plants, so adding it when you are starting your seeds is often a better option. Try to add it to the lower layer of potting mix, and don’t let it come in direct contact with the seeds. Even organic fertilizers can burn if you use too much.

Knowing When Seedlings Have Had Enough Food

How much to feed seedlings will take some experimentation. Keep an eye on how well your seedlings are filling out. Too much fertilizer can cause a flush of tender, lanky growth, which is not what you want. Ease back on the fertilizer if this is the case.   At this point in a seedling’s development, you should be more interested in growing a healthy root system than sending up a lot of green leaves.

Moreover, each plant—even those of the same species—will react a little differently to fertilizer. But in time you should get a feel for how much food it takes to keep your seedlings robust while they build up the strength to be moved outdoors into the garden.

New plant seedlings can feed themselves up until their first true leaves appear. Here are tips on how, when, and what to feed your seedlings.

How to care for your cannabis seedling

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Contents

  1. What happens during the seedling stage?
  2. Choose the right container
  3. Be mindful of how much you water your cannabis seedlings
  4. Know the signs of nutrient deficiencies
  5. Choose the right lighting
  6. Keep your environment at the right temperature and humidity
  7. Get out there and grow your seedling into a full-grown marijuana plant

When you’re growing cannabis, you want to keep your plants strong and healthy through every stage of the growing process — and that includes the seedling stage.

The seedling stage can be an especially vulnerable time in the growing process. The cannabis seedling is in need of a lot of TLC to grow into a healthy cannabis plant.

In the seedling stage the cannabis seedling is in need of a lot of TLC to grow into a healthy cannabis plant. Photo by: Gina Coleman/Weedmaps

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But what does that TLC look like? What steps do you need to take to support your cannabis seedlings through the seedling stage and as they grow into mature marijuana plants?

Let’s take a deep dive into how to care for your baby marijuana plant so you know exactly how to take care of your growing seedling and make sure it grows into a healthy, mature cannabis plant.

What happens during the seedling stage?

Before we jump into how to care for your cannabis seedling, let’s quickly cover what happens during this grow stage.

The growing process has four key stages: the seed germination stage, the seedling stage, the vegetative stage, and the flowering stage. Once the cannabis seeds germinate and are placed into their growing medium (like a potting mix), they start to root into the soil as the stem grows upward, sprouting two cotyledon leaves, which help the plant absorb light and continue to grow.

As the plant grows, it starts to produce more fan leaves — and those leaves continue to develop the ridged edges that you’ll immediately recognize as the marijuana plant. As more leaves grow, more ridged edges develop until finally, the plant is fully grown with each leaf reaching its maximum number of edges (which can be anywhere from 5 ridges per leaf to upwards of 10).

This stage — moving from germinated cannabis seeds to cannabis plants with the maximum number of ridged edges per leaf — is the seedling stage.

The seedling stage is an incredibly important part of the growing process; because the cannabis plant is still young and fragile, proper care is essential if you want to lay the foundation for a healthy mature plant.

But what does that care look like? What are the key things to know when it comes to how to take care of marijuana seedlings?

Choose the right container

Your cannabis seedling needs space to grow. But too much space and too little space can both create problems for your plant.

If you try to grow your seedling in a container that’s too large, the root system won’t be able to absorb all the water in the soil. If you start growing your seedling in a container that’s too small, the roots won’t have space to extend and will start to wrap around themselves, which will also impact their ability to absorb water.

Choosing the right pot is an essential part of caring for your growing plant. You need a pot that’s going to give the root system space to grow, but not so much space that the roots won’t be able to absorb all the water in the soil. You should also make sure the pot has drainage holes to get rid of any excess water that could overwhelm the plant.

Choosing the right pot is an essential part of caring for your growing plant. Photo by: Gina Coleman/Weedmaps

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Be mindful of how much you water your cannabis seedlings

When it comes to watering your seedlings, you want to give them the water they need to thrive. But too much water can actually have a negative impact on the growth process, so it’s important to be mindful of how much you water your seedlings.

The root system of a seedling isn’t elaborate; the roots are small and don’t need much water to grow. Misting the plants with water once or twice a day should be plenty to give them the hydration they need to grow.

If you’re not sure how much water is too much water, keep in mind that you want the growing medium (AKA the soil) to be damp and moist — not soaked and oversaturated.

Know the signs of nutrient deficiencies

A nutrient deficiency can cause serious issues for your growing plant, so part of proper care is knowing how to spot the signs of a nutrient deficiency.

Nutrient deficiencies can come from a variety of places. “Hot” potting mixes that contain too many nutrients could cause nutrient toxicity. On the other end of the spectrum, under-watering can cause a deficiency in the key nutrients your plant needs to grow.

Some red flags that signal your seedling may have a deficiency in nutrients (or nutrient toxicity) include:

  • Dark coloring (cannabis seedlings should be a vibrant shade of green)
  • A burned appearance on the tip of the leaves
  • A curling on the tip of the leaves
  • Yellowing leaves

If you notice any of these issues with your plant, it could be the result of too many or too few nutrients. You’ll need to adjust your growing strategy to support your plant’s health.

Choose the right lighting

Like any plant, seedlings need light in order to grow and thrive. But not all light is created equal. If you want your seedling to grow into a healthy cannabis plant, you need to expose it to the right type of light.

If you’re growing your seedlings outdoors, they’ll need to be exposed to as much sunlight as possible. Keep them in the sun from sunrise to sunset; the more sunlight exposure they get, the better.

If you’re growing your seedlings outdoors, they’ll need to be exposed to as much sunlight as possible. Photo by: Gina Coleman/Weedmaps

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But growing your seedlings outdoors can be tricky. Because you can’t control sunlight, there’s no way to ensure your cannabis seedlings are getting the light they need to grow properly. A cloudy day can prevent your seedlings from getting enough light and throw off your entire growth process.

Growing your seedlings indoors with artificial light gives you more control over the process, making it easier to ensure your plants are getting enough light each day. If you’re growing with artificial lights (compact fluorescent lights that emit cooler, blue spectrum light are especially effective), aim to give your plants 18 hours on and six hours off each day.

Keep your environment at the right temperature and humidity

Environmental conditions are essential to growing healthy cannabis seedlings, and some of the most important conditions to control are temperature and humidity.

The temperature in your grow environment shouldn’t exceed 80 degrees Fahrenheit, otherwise the seedlings may grow too tall. (You should also plan on lowering the temperature at night to about 70 degrees Fahrenheit.)

You should also aim to keep humidity in the grow environment at a higher level, typically around 70 percent. That way, the plants can absorb moisture from the environment to develop stronger roots without getting weighed down by over-watering.

Get out there and grow your seedling into a full-grown marijuana plant

Watching your cannabis seeds transform into seedlings is an exciting part of the growth process. And now that you know how to care for your cannabis seedling, you should have everything you need to transform your seedling into a mature, healthy, and flowering cannabis plant.

How to care for your cannabis seedling Copy article link to clipboard. Link copied to clipboard. Contents What happens during the seedling stage? Choose the right container