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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.

Cannabis Nutrients: Why, How, And When To Feed Your Plants

Cannabis plants are sensitive to nutrients, and there’s a fine line between properly feeding your plants and burning them with chemicals. Find out everything you need to know about properly feeding cannabis plants in our guide!

A full rundown on why and how to feed your cannabis plants.

  • 1. Understanding cannabis macro and micronutrients
  • 2. Not all cannabis fertilisers are made equal
  • 3. Nutrient requirements for seedlings, vegging, and flowering weed plants
  • 4. How to read a feed chart: How often should I feed my weed plants?
  • 5. How to prepare cannabis nutrients
  • 6. The importance of PPM, pH, and water temperature
  • 7. Tips for better feeding
  • 8. Recognising cannabis nutrient-related problems
  • 9. Organic vs chemical fertiliser for cannabis
  • 10. Wrapping your head around cannabis nutrients
  • 1. Understanding cannabis macro and micronutrients
  • 2. Not all cannabis fertilisers are made equal
  • 3. Nutrient requirements for seedlings, vegging, and flowering weed plants
  • 4. How to read a feed chart: How often should I feed my weed plants?
  • 5. How to prepare cannabis nutrients
  • 6. The importance of PPM, pH, and water temperature
  • 7. Tips for better feeding
  • 8. Recognising cannabis nutrient-related problems
  • 9. Organic vs chemical fertiliser for cannabis
  • 10. Wrapping your head around cannabis nutrients

All the nutrients needed for cannabis plant development are naturally present in the environment. However, to help your plants develop even faster and produce a better end product, you’ll want to feed them with fertiliser—concentrated nutrients.

Below, you’ll find all the information you need to know about when, how, and how much to feed your cannabis plants.

UNDERSTANDING CANNABIS MACRO AND MICRONUTRIENTS

Cannabis plants require three nutrients in large quantities. These macronutrients are nitrogen (N), phosphorus (P), and potassium (K), and they form the cornerstone of cannabis plant health. As such, these three nutrients usually feature front and centre on fertiliser products in the form of an NPK ratio. The higher the number for each value, the higher the concentration of that particular nutrient.

However, cannabis needs more than just three nutrients to survive and thrive. It also counts on secondary nutrients like calcium, magnesium, and sulfur to play vital roles in plant growth:

  • Calcium is important for cell wall development, can help reduce soil salinity, and improves water penetration when used as a soil amendment.
  • Magnesium plays a key role in photosynthesis and carbohydrate metabolism, and also helps with the stabilisation of plant cell walls.
  • Sulfur is necessary for the formation of chlorophyll and the production of proteins, amino acids, enzymes and vitamins, and protects plants against disease.

Beyond this, plants also make use of several other nutrients in small quantities (micronutrients) that are nevertheless extremely important. These include boron, chlorine, copper, iron, manganese, molybdenum, and zinc. While these aren’t the main nutrients plants use for food, they still play very important roles in various aspects of plant health.

NOT ALL CANNABIS FERTILISERS ARE MADE EQUAL

There are many different brands of cannabis nutrients on the market, and they can differ considerably.

Typically, cannabis fertilisers will vary in the four following areas:

  • Nutrient ratio: Different brands use different nutrient ratios they consider optimal.
  • Ingredients: Different fertiliser brands can achieve the same nutrient ratios using completely different ingredients, ranging from the most chemical (or “artificial”) to the most natural.
  • Soil or hydro: Soil nutrients are very different from hydro or soilless nutrient solutions. Make sure you only use fertilisers designed for your growing medium.
  • Supplements: Many fertiliser brands also make “supplements”. These products typically contain low NPK ratios and instead feature other nutrients designed to boost certain aspects of growth. Some supplements, for example, are essentially molasses.

In general, we recommend you focus more on meeting your plants’ demands for macro and secondary nutrients before pumping them full of supplements. Going overboard with nutrients can result in chemical interactions or nutrient burn, which can significantly impact the size and quality of your yield.

Once you’ve nailed feeding your plants with these core nutrients, feel free to move on to a more complex feeding schedule to produce bigger, more potent harvests.

Wondering when and how to feed your cannabis plants? Click here for the ultimate guide to cannabis nutrients and how to use them to produce excellent harvests.