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The Ultimate Seedling Care Guide

If you plan on starting any of your plants by seed to later transplant out in the garden, this seedling care guide will provide you with all of the tips and care your seedlings need for healthy growth!

Plant seedlings growing in seed starting trays

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Starting your own seeds indoors or in a greenhouse is a fun process but there is a lot required after planting the seeds. In order to get your seeds to germinate and continue growing into healthy young plants, you need to provide them with the proper care.

So in the seedling care guide, I’ve provided all of the essential care that your young seedlings need in order to grow healthy so that you can successfully transplant them out into the garden when the time arrives.

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Seedling Care Requirements

Once you plant your seeds in individual pots, seed trays, etc. there are 3 things that are most important for your transplants to grow successfully which include,

  1. Water
  2. Temperature
  3. Light

The most common time of year to start seedlings is during the winter prior to spring planting. So you will likely need to start your seeds indoors, in a greenhouse, or in a seed starting tray with a humidity dome.

I have had great success in my greenhouse and I just started off with an inexpensive greenhouse on Amazon because when it comes to starting seeds it serves its purpose. 

Plant Your Seeds

The most important thing when you plant seeds is that you use a “seed starting mix” and not just regular potting soil.

So here is a basic seed starting outline,

  1. Fill your planting container of choice with seed starting mix. I prefer reusable platic pots like these.
  2. Water until you thouroughly dampen the seed starting mix.
  3. Make a small hole in the center of the pot at the required depth of whichever seed you are planting.
  4. Cover the seeds with seed starting mix and gently water again.

After you plant your seeds follow the care requirements below.

One of my favorite crops to start by seed is tomatoes because you have so many more options of seeds to buy than the plants that are available at most garden centers.

So if you’re thinking of starting your own tomatoes you can learn more in my post, How to Grow Tomatoes By Seed.

Seeds getting planted in seed starting pots

Watering Basics for Seedlings

From planting seeds to germination, keep the soil constantly moist but not overly saturated.

It’s better to water deeply versus just misting the top of the soil. Especially if you’re using a seed starting mix that should drain well. 

After germination water your seedlings in the morning to prevent condensation on the leaves during the night which can promote disease.

As your seedlings get bigger and more mature, rule number one is to always check the soil before watering.

If plants are wilting from drought you’ve waited too long. But wilting can also be a symptom of over-watering or that the air is too cold. 

So it’s important to feel the soil to check if they really need water. 

Watering young seedling with a watering can

Symptoms of Overwatering

  • Growth of blue-green mold on top of the soil.
  • Plant disease or poor germination.
  • Slugs feeding on plant leaves.
  • Slow plant growth (there is less oxygen in the soil and roots need to breathe).
  • Yellow leaves, yellow splotches on leaves, yellowing leaves falling off of the plant.
  • Wilting (wilting is not only from drought).

Variables That Affect Watering 

  • The more sunshine plants receive, the more water they need.
  • The more ventilation and airflow they receive, the more water they’ll need.
  • Different plant varieties (for example, succulents need less water than vegetable plants).
  • Different stages of plant life (seedlings need constant moisture and should never dry out, but should not be drowning either).

Temperature Requirements

In order for seeds to germinate, there is a minimum soil temperature, an optimal temperature, and a maximum temperature. 

We want to be somewhere close to the optimal temperature range which for most plants is 60-80° F. But you should refer to the seed packet for each specific plant. 

If the temperature isn’t right it’s very likely to have germination problems.

Germination Problems & Solutions

One of the most common problems people face when starting seeds is that their seeds don’t sprout. If your seeds are not germinating it’s likely due to one of the following reasons.

  • Soil is too hot or too cold.
  • Seeds are not viable (likely too old).
  • It’s too soon (some seeds have a long germination period).

So if you believe any of these could be the reason for your germination problems check out the solutions below.

Germination Solutions

Luckily during the cooler months when you are most likely to be starting your seedlings, it’s unlikely to have soil that is too hot.

But if you are starting your seeds in a greenhouse that is extremely warm you should open up the doors during the day. 

If you are past the expected date of germination and you have good seeds that should be viable it’s likely that the soil is not warm enough. 

If that is the case, make sure your greenhouse is completely closed up to keep it as warm as possible.

Or if you are starting your seeds indoors you may need to place them on a heat mat until they sprout. 

If the seeds still do not germinate it’s likely that had a bad batch of seeds. 

If you’re looking for a great way to keep track of your seed inventory and how old they are, be sure to check out my Gardening Planner HERE.

Germinated seedlings in individual pots

Lighting Requirements for Seedlings

For the sake of simplicity, I won’t go too far into the science of light for plants but I will go over the basics. 

Plants need light to grow. They convert light into energy (sugar) in the process of photosynthesis. But keep in mind photosynthesis does not only require light. It requires light, carbon dioxide, a temperature generally between 32-100° F, and water. 

Without one of these elements, the growth process will fail or be slowed down.

Here is the basic process of photosynthesis,

  1. Light enters the chlorophyll of the leaf.
  2. Special structures combine the energy from the light with carbon dioxide & water.
  3. Through the process of photosynthesis, those elements convert into oxygen and sugar.
  4. The oxygen burns off in chemical reactions and goes into the air as a component of water vapor.
  5. The sugar is fuel and burns off within the plant to provide the plant with the energy it needs to grow.
  6. At night, plants burn off the sugars through the process of respiration. 

Luckily you don’t have to worry so much about the science of it all but it’s important to know the basics. As long as your plants are getting plenty of light and go through a dark period (night-time), they should be good to go. 

However, there are many symptoms we should pay attention to when we are growing our seedlings that are directly related to light.

By recognizing these low-light symptoms we can help our plants grow as healthy as possible. 

Symptoms of Low-Light 

If you recognize any of the symptoms below you need to provide additional light for your plants which we will talk about further down. 

  • Slow plant growth.
  • Spindly, slender growth and stretching of stems (most common sign).
  • Yellowing of lower leaves (could also be from a nitrogen deficiency). 
  • Plants bending drastically toward the light.

Providing Additional Light

The first step is to see if there are any simple fixes. 

  1. Is there something shading your plants during part of the day?
  2. Could you move your plants to an opposite area inside of the greenhouse that gets more light?
  3. Can you move your plants to an area indoors with more sunshine?

You can add white rock on the south side of your greenhouse to help reflect more winter light inside. 

Or if your plants are still suffering from low-light conditions you will need to set up a grow light

Keep the lights on for 16-18 hours per day and then turn them off to give plants a period of darkness. To make things even easier you can set up a light timer.

Once your seedlings get sufficient light you should notice obvious low-light symptoms improve such as spindly growth, stretching toward the light, and the yellowing of leaves.  

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Fertilize Your Seedlings

When it comes to fertilizing your seedlings it’s important that you don’t fertilize too soon or fertilize too much. So if you’re unsure, you’re better off waiting.

But once your seedlings have their second set of leaves also known as their true leaves you can fertilize 1-2 times per week with a fertilizer such as the 20-20-20 Premium Fertilizer from Hoss.

Harden Off Seedlings Before Transplanting

The last important step for healthy seedlings is that you harden them off before transplanting them out into the garden.

But before we go over how to do that I want to quickly go over what hardening off means.

What Does Hardening Off Seedlings Mean?

In simple terms, it is the process of preparing your young plants for the outdoors. Until now, they have had a very controlled environment. Most likely indoors or in the greenhouse.

So if you move the seedlings directly from those mild conditions straight into the garden where day and night conditions are not as consistent it will be a much more stressful transition.

How to Harden Off Seedlings?

You should start hardening off your seedlings 1-2 weeks before your outdoor transplanting date.

Throughout the process, you will be gradually be exposing your seedlings to the outdoors and increasing exposure every couple of days.

Here is the basic process of hardening off,

  1. Move your seedlings outside for 1 hour in an area protected from the direct sunlight and wind.
  2. After time is up, bring the seedlings back indoors or into the greenhouse.
  3. Increase the time spent outdoors by an hour each day. But if there is any drastic change in weather conditions either below 45° F, rain, or high wind, don’t keep them outdoors.
  4. After a few days in an area protected from the direct sunlight you can start gradually exposing them to the sun.
  5. Start by letting them only receive direct morning sun.
  6. Each day they will get more acclimated and be able to tolerate more sunlight.
  7. After a week or so, leave the seedlings out overnight as long as nighttime temperatures will be above 45-50°F.
  8. At this point your seedlings should be ready to transplant out into the garden!

When you are ready to transplant be sure to read my 5 Secrets to Transplanting Vegetables Successfully.

Young transplants ready to be transplanted in the garden

In Summary

I hope you’ve found the tips and information in this seedling care guide helpful!

Starting seeds is a fun and rewarding process but it takes patience and a lot of observation. But putting in the time to grow healthy seedlings means you will have healthy plants to transplant into the garden!

Comment below if you have any questions!

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Young seedlings getting watered

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