Oct 4, 2021 11:19:42 AM / Brooke Loeffler / starting seeds indoors

How To Start Seeds Indoors

Getting a head start on your garden can be exciting. However, over-eagerness for an earlier harvest can sometimes lead to weak and leggy seedlings that don’t survive the transplant process. Here we will learn how to properly start seeds indoors and which plants will be most successful.

How To Get Started

Make A Planting List

Start by making a wish list of what you would like to grow. Find out which plants are compatible with your growing zone and have your soil tested so you know what amendments you will need. Learn more about the plants on your list, such as their light requirements, harvest schedule (how many days from sowing till harvest), water requirements, etc.

Make A Planting Map

Take a look at how much space you have to work with and ask yourself some questions to help you know where your seeds will end up:

  • Which plants can be started indoors vs. directly sown into the ground? (keeping reading for more info)
  • Which plants can be grown in containers or vertical planters?
  • Which plants will take up the most garden real estate? (I am looking at you pumpkins, melons, cucumbers, and squash!)
  • Where should sun loving plants go?
  • Where should shade loving plants go?
  • Which plants make good or bad neighbors?
  • Which plants will need cages, trellises, or other growing supports?

Have A Backup Plan

Even gardeners with green thumbs kill plenty of plants. Research your local nurseries or identify which websites you would like to try if something goes wrong with your seeds. You may even find plants you had not thought of before! You can also save some of your seeds in case you need to re-sow and try again.

Which Seeds Should I Start Inside?

Not all seeds are happy with our attempts to get a leg up on mother nature. Some seedlings simply do not tolerate the transition from indoors to outdoors very well.

Which seeds should I start indoors?

Seeds You Can Start Indoors

The best seeds to start indoors do not have tap roots, bulbs, or tubers. Seeds that are sensitive to the cold or those with longer harvest schedules are also good candidates.

  • Tomatoes
  • Peppers
  • Broccoli
  • Cauliflower
  • Cabbage
  • Celery
  • Leafy greens (can be started inside or outside, but starting seeds indoors can help give you an advantage before the heat of the summer makes them bolt and flower)
  • Some vine based plants like cucumbers, pumpkins, and squash can be started indoors but can outgrow your seed area quickly

Direct Sow Outside

Plants with tap roots, bulbs, or tubers do not transplant well and should be planted directly outside. Cold tolerant plants and those with shorter harvest timelines will also do better being planted outside.

  • Potatoes
  • Carrots
  • Radishes
  • Beets
  • Onions
  • Parsnips
  • Rutabagas
  • Sweet potatoes
  • Melons
  • Squash
  • Pumpkins
  • Cucumbers
  • Beans
  • Leafy greens (arugula, spinach, chard, lettuce, see above) 
  • Peas
  • Corn

When To Start?

Starting dates can vary quite a bit depending on location, first frost, time of year, and which seeds you are working with. Fortunately, the trusty folks at The Farmer’s Almanac have created a calculator that works with these variables to give you planting dates for your specific area:

  • Click here to get your custom planting calendar

How To Start Seeds Indoors

Follow Seed Packet Instructions

Read and follow the instructions for each seed type:

  • Pre-planting instructions (ie. soaking)
  • Planting depth and spacing
  • Moisture levels
  • Temperature range

Lighting

Starting seeds in a window can be problematic for a number of reasons. Light is typically coming in from an angle which causes sprouts to lean. Windows can’t usually provide long enough light exposure and seedlings become stretched and “leggy.” Windows can also expose seeds to drafts and temperature fluctuations. Unless you have a sunny and warm greenhouse, you will see greater success with growing lights. You don’t need to purchase expensive hydroponic lighting systems because your plants will eventually move out into the sun. Indoor grow lights can be very affordable!

Here are a few grow light tips:

  • Select lights that provide the full light spectrum
  • Built in timers can be extremely helpful (at least 12 hour lighting sessions)
  • Select lights that can be adjusted so you can start 2-4 inches above the soil and adjust their height to maintain 2-4 inches above seedling growth (too close and you can scorch baby leaves, too far and your seedlings will be leggy and weak)
  • This light can also be helpful if you want to bring any plants indoors during the winter!

Seedlings under a grow light

Containers

There are a lot of DIY, upcycled, and affordable seedling containers out there. Whatever container you use, here are some universal rules:

  • Make sure water drains properly
  • Don’t use upcycled materials with heavy glues or paints that can leach into your soil
  • Thoroughly clean reusable seedling containers before planting new seeds
  • Have some larger containers at the ready in case your roots need more room and it is still too cold to move them outside
  • Label your containers so you can be sure you are applying the right instructions to the right seeds
  • If you plant multiple seeds in 1 container, thin out the seedlings that are struggling to give more room to the ones that are thriving

Temperature Range

Keep your seeds away from draughts and in a location where you can keep them in their required temperature range. A seed heating mat may only be necessary if you are starting seeds in a cooler basement, garage or shed. Gentle heat can help some seeds germinate faster, but prevent others from germinating. You typically won’t need heating mats once seeds have germinated into seedlings.

“Hardening”

Plants started indoors have lived a very pampered life. They will need to be “hardened” or gradually introduced to the light, wind, and temperature variations of the great outdoors. Placing your seedlings outside for a few hours at a time in sheltered, dappled sunlight will help them adjust. Gradually increase their outside time each day for at least a week.

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