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March 20, 2022

Indoor Seed Starting


The days are getting warmer, and Spring is finally here! Get a head start on the growing season by starting some of your favourite flowers, fruits, and vegetables indoors from seed. The risk of frost will have passed in no time at all, and you’ll have strong and healthy seedlings ready to transplant once the regular growing season begins.

Tomatoes are by far the most popular choice that Canadians grow in their home “vegetable” gardens, but there are so many other easy options that you may want to explore.

Here are some helpful hints on how you can start sowing the seeds of your summer garden right now.

Indoors or out?

Do I start my seeds indoors or outdoors?

Most seed packets will indicate where best to plant your seeds and when to start them. If planting indoors, it may say to ‘start seeds indoors eight weeks ahead of the last frost date.’ Indoor planting will help ensure you give your seedlings enough time to get strong and not transfer them outside too early.


A good rule of thumb for measuring the final frost in Ontario has always been the May 24th weekend, and you should not consider planting your seedlings outdoors before this date.


If your seeds require ‘direct sowing’, they will be best started outdoors after the final frost. Plants that require direct sowing may not transplant well from indoor plants as their roots are too delicate to move from indoor to outdoor growing.  They also tend to be faster growing so don’t require the indoor head start.


So, when will my plants bear fruit?
Your seed packets will usually reference when you should be able to enjoy your harvest. For instance, most tomatoes require about 100 days of growth before they will bear fruit, so if you want to see fruit at the end of July, you need to count back 100 days when you start your seedlings to achieve this goal.


Let’s look at some helpful seeding tips and techniques to ensure your seeds grow into healthy plants.


Pick plants that will thrive in your area – you want plants that will be able to do well in our climate, tolerate the summer’s heat, reach maturity before frost, and generally thrive in your local climate.


Plant vegetables and plants that you like to eat and bring you joy – seems obvious, but there’s no point in planting things that no one in your family enjoys!


Try a variety of seeds – experiment with vegetables, flowers, herbs, and even research companion planting to find out what plants grow best together.


Don’t buy more seeds than you can use in a season – seeds will generally grow into healthier plants when the seeds are fresh. If you have more than you can use – share with other like-minded gardeners.


Choosing and preparing your pots
One of the essential steps in your planting process is ensuring the pots you use are properly prepared for your seedlings.


If purchasing new pots – choose the best pots to start your seedlings. Small plastic pots, seedling trays, or peat pots are preferred over clay pots for seedlings to ensure the right level of moisture. Plants with more fragile roots do best in cell packs and plug trays.


If you are using existing pots – make sure that your pots are clean and disinfected from the previous year’s growth. This will ensure that no harmful bacteria or bugs infest your seeds, causing your seedlings to fail. Use a gentle soap and water to thoroughly clean your pots and containers, followed by bleach for deeper sanitation.


Remember to only plant the recommended number of seeds in your container. Do not overcrowd the seedlings, or you will quickly find your plants wilting. Pots should have adequate drainage to prevent your seedlings from drowning and reduce the chances of fungal infections.


Choose a seedling specific soil
You will need to choose a seed starter mix to help your seeds properly germinate. Traditional potting soil may be too heavy and prevent seedlings from reaching maturity.

Seedling soil mixtures are specifically designed for seed starting and are ideal for starting plants and vegetables.

When prepping the soil for planting, you can lightly pre-dampen the soil, so it is moist but not soaking and evenly mixed.


Planting your seeds
You will want to refer to your seed packet to determine how deeply to plant your seeds. For instance, larger seeds need to be planted deeper than smaller seeds. Plus, there may be special instructions to prepare your seeds before planting – such as soaking – so you will want to make sure you refer to your seed packet, so your plants get off to the best start possible.

Add your pre-dampened soil loosely to your pots and follow the instructions on your seed packet for planting. Allow for two or three seeds per pot.


Proper water techniques for starting your seedlings
When you first plant your seeds, you will want to lightly water the pots from the top down to ensure that the top layer does not dry out. Smaller seeds that are not planted as deeply only need to be lightly sprayed with a spray bottle.


Covering for germination
To help speed up germination, cover your plants with a plastic sheet or a plastic dome. Most seed kit trays come with plastic covers for this purpose. As soon as the green sprouts pop through the soil, remove the cover.


Bottom watering techniques
The bottom watering method is an excellent way to prevent overwatering as it allows for water to flow up through the plant and establish stronger roots. This method also helps to eliminate the growth of fungus and pest infestation.

You will want to set your pots or seedling trays on a larger tray to bottom water. Fill the bottom tray with about an inch of water and allow 15 to 20 minutes for the water to absorb into the plants. Then discard any excess water from the bottom tray and replace the seedling tray on the empty tray to allow any excess moisture to drain out.

It’s best practice to water your seedlings once per day, either in the morning or the evening, and for ideal growing, the soil should feel like a wet sponge.


Ensuring proper lighting
Your seedlings will require up to 14 hours of continuous light when first germinating. You may be able to get away with a good south-facing window for your seedlings if they are placed relatively close to the windows. If you are just starting out, this may be the best way to go but may result in some wastage and what are known as tall, leggy seedlings.

Or, if you want to ensure your seedlings get off to an excellent start, you could invest in some indoor grow lights. Indoor plant lights also allow you the flexibility to grow your seedlings anywhere in the house.


There are many lighting kits available for the beginner to the advanced gardener. It may be an initial investment, but most gardeners who start from seedlings would agree that it is well worth it in the long run for strong, healthy seedlings.


Monitor indoor temperature
Seeds require warm, stable growing conditions to begin germinating and do best at temperatures of between 65F to 75F or 18C to 23C.

Fertilizing your seedlings
A balanced fertilizer specific to seedlings will encourage and establish strong root growth. Seedlings can be fed approximately every two weeks.


Trimming your seedlings to make them stronger
As your seedlings mature, you may notice some thin, weak seedlings. You will want to trim these back to allow the other seedlings to thrive. Use a small pair of scissors to snip these back so that you do not damage the root base.


Prep seedlings for transplanting
Before long, it will be time to transplant your seedlings from starter containers to the garden. Seedlings started indoors need a gradual transition before being moved outdoors. The seedlings should be strong enough to move outside once the roots have matured enough and are poking out the bottom holes of the pots. However, it is also essential to ensure you are moving outdoors in the proper planting season stipulated for your plant.

The transition process to the outside growth cycle for seedlings is called Hardening Off.  The plants will need to have a gradual introduction to outdoor temperatures, and it will be best to start with a few hours a day over the course of a week until they gradually can tolerate an entire day.

You will need to keep a close watch on the seedlings to ensure they do not get too hot from overexposure to the sun, too cold from dropping temperatures we may experience in the Spring, or too much precipitation from a heavy rainstorm.


Planting your seedlings outdoors
Once your seedlings have reached a point where they are strong and can tolerate outside temperatures, they will be ready to plant in a garden. Plant in fresh, nutrient-rich soil and water thoroughly so the root system can begin settling into its new home.

Make sure you reference the growing conditions for sunlight to ensure you plant your seedlings in the optimal area where they can thrive. Cover your seedlings as necessary to prevent creatures like squirrels or rabbits from digging up your hard work.

Within a few weeks, you will see your seedlings quickly grow into fresh flowers or vegetables for you to enjoy all season long.


Sheridan Nurseries offers an abundant selection of seed starting and propagation supplies and is your one-stop-shop for getting your garden started this spring.


The experts at Sheridan Nurseries can help you find the right supplies to begin growing plants from seed. From seedling pots to planting tools, Sheridan Nurseries can help you sow the seeds of a beautiful garden.