Seedling Fertilizer

When my seedlings begin to grow their first set of true leaves, I start looking at my seedling fertilizer options.  


True Leaves

True leaves are the first set of foliage leaves after the seedling leaves (cotyledon) have emerged.  When the seedling first emerges from the soil, it bursts out of its seed coat and simultaneously sends a stem above ground and a root below ground.  Some plants have only one leaf that will emerge (monocot) and others have two leaves (dicot).  For example, onions are a monocot while tomatoes are a dicot.  The cotyledon leaves and tap root are able to provide the plant with enough nutrition to start the plant’s initial growth.  After a week or two of cotyledon growth, the plant will form its first true leaves.  The true leaves will have the appearance and function of all future leaves.  True leaves may look dramatically different from their cotyledon leaves.  

After the plant has produced its first set of true leaves, fertilizer applications should begin.  We start seeds in small containers with soilless mixtures that are not very rich in nutrients for the plant.  If we want our plants to continue to grow at a healthy rate, we need to provide them with nutrients in the form of fertilizer!.  


Seedling Fertilizer

Seedlings are very delicate. It is important to provide them with nutrients but not overdo it.  Less is more in the world of seedling fertilizer.  I look for a well balanced fertilizer or any fertilizer that is designed for the ‘grow’ phase of the plant’s life.  A seedling fertilizer may have an NPK ratio like 4-3-3.  My favorite seedling fertilizer is Neptune’s Harvest Fish & Seaweed (2-3-1).  Its phosphorus level will encourage strong root growth while the nitrogen level will encourage leafy green growth. The seaweed component is rich in many micronutrients and plant growth promoting hormones. I use Neptune’s Fish & Seaweed fertilizer at 1 TSP per gallon after my seedlings have sprouted their first true leaves once per week.  As my seedlings continue to grow, I gradually increase my dosage of fertilizer until I am using 1 TBSP per gallon. Once I reach 1 TBSP per gallon I do not increase my dosage.  


Other Important Notes:

  • Check your pH
    • Depending on your water source (Well water, City water or Reverse Osmosis water), your water may be very basic or very acidic.  Additions of fertilizer may also change your pH.  A desirable pH value for seedlings is between 6.5-7.0.
    • An inexpensive pH test kit may be purchased for less than $10.  A digital pH pen will range from $40-$300+.   
  • Remember, less is more when it comes to seedling fertilizer.  Whatever fertilizer you choose will have a recommended use rate on its label.  Look at this recommended rate and cut it in half to start.  You can always add in more fertilizer later.  You cannot remove too much fertilizer once it has been applied.
  • Most liquid fertilizers are concentrated.  This means that a small amount of fertilizer needs to be added to water to dilute it.

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