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Spring is here! Let's start seeds!

March 11, 2021
Green basil seedlings, photo taken from above

Spring weather is finally here, and it’s time to start planting seeds. Starting seeds at home doesn’t need to be expensive, fancy or difficult.

Serious gardeners who want to start large quantities of seeds will benefit from certain investments like artificial lights and heating pads. But for gardeners who are growing a small number of plants or just starting out, materials you already have on hand may suffice. 

When do I start my seeds?

We have a great guide to starting seeds, with a table showing you when to seed different vegetables.

In general, now is a great time to start seeding your cool-season crops like lettuce and Brassicas, and it’s best to wait until early April to start seeding warm-season crops like tomatoes and peppers. 

What is the best type of soil to use?

A pre-mixed potting soil specifically designed for seedlings is usually the best option for starting seeds. Seeds need to grow in soil that drains well to prevent damping off. These mixes have an optimal blend of sand, silt, clay and other materials such as peat, coconut coir and vermiculite.

Pre-made mixes also have enough fertilizer to support seedlings until you’re ready to transplant them into the garden. However, these mixes do not have enough fertilizer to support plants to maturity. So if you’re planting into a container, make sure to use a separate soil mix that is specially formulated for containers. 

What supplies do I really need? 

Person planting seedlings in a plastic tray with individual cells filled with dirt.
Plastic trays are efficient and low cost for starting seedlings

When I look at photos and videos of seed starting setups and start to figure out the price of setting up a similar system, it can get overwhelming pretty fast. The good news is that most of us don’t need state-of-the-art systems for starting seeds.

There are five basic requirements for starting seeds successfully indoors, and they can be achieved with varying degrees of investment and sophistication. These requirements are light, warmth, containers, water and humidity. 

A source of light

All plants require light to grow. In the short term, a very sunny window is sufficient to start your seedlings. This can work well if you plan to transplant your seedlings within 3 to 4 weeks of germination. For most home gardeners, starting seeds in a window works well, and supplemental lighting is not required.

If you plan to start your seedlings more than a month or so ahead of time, or you lack a sunny, south-facing window, grow lights may be necessary.

If your plants do not have enough light, they can get “leggy.” This happens when they stretch to reach towards a light source and can result in thin stems that are not strong enough to support the plant. 

Check out our lighting for indoor plants and seed starting page to learn more about the pros and cons of different types of supplemental lights. 

A source of warmth

Most seedlings germinate best in warm soil. For cool-season crops like lettuce, broccoli, kale and pak choi, soil around 50 degrees F is optimal. For warm-season crops like peppers and tomatoes, soil around 65 degrees F is ideal.

When the soil is cool, your newly sprouted seeds are more likely to experience damping off. Keeping your soil warm allows for quick growth and healthier plants. 

If you have a south-facing window and an area near it that gets quite warm during the day, this is likely sufficient for your garden seeds.

For gardeners who lack a warm window, or for serious gardeners who want to grow quite a few transplants, investing in a heating mat may be a good idea. Heating mats are electrically powered and sit underneath your germination trays to heat your soil from the bottom. They can be a bit expensive upfront ($25 for a 10’’x20’’ mat, up to $150 for a 20’’x60’’ mat), but they last for many years. 

Pots

Rows of tomato seedlings in small plastic pots at a farmers market.
Individual plastic pots can be used again provided they are cleaned between uses

Next, you’ll need something to hold your potting soil. The options for pots are nearly endless. Some of the most common options include: 

  • Plastic trays: An efficient way to start seedlings is to buy plastic trays with numerous cells already molded into the tray. These trays come with various cell sizes, ranging from 128 cells per tray (very small cells for herbs, things you plan to transplant quickly, or things that will eventually be transplanted to larger pots) all the way to 50 cells per tray. Trays range in quality; some are disposable and use cheap, thin plastic, and others are re-usable with sturdier plastic. They tend to be space-efficient, allowing you to grow many plants at once without having to deal with so many pots. 
  • Plastic pots: Another plastic option is to purchase individual pots (2x2 or 4x4 pots). These can be practical if you only plan to grow a few things, or if you plan to share plants with neighbors. They can be re-used from year to year. 
    Seedlings planted in coconut coir square pots in a tray.
    Seedlings in coconut coir pots
  • Peat or coconut pots: Peat and coconut coir pots have gained popularity in recent years as an alternative to plastic. These pots are biodegradable and can be placed directly into the soil when you are ready to transplant. They work well for vegetables like cucurbits (cucumbers and melons), which are quite sensitive to root disturbances. Traditional biodegradable pots were made of peat, but due to sustainability concerns, there has been a shift towards using coconut coir, a byproduct of the coconut industry. 
  • Newspaper or toilet paper roll pots: If you’re in the DIY spirit, you can make your own pots out of newspaper or toilet paper rolls. These pots may be more likely to disintegrate over time as you water your seedlings but can work well for seeds you plan to transplant relatively soon after seeding. 
    Seedlings planted in tubes made of rolled up newspaper.
    You can make your own pots out of newspaper or toilet paper rolls
  • Soil blocks: Finally, soil blocking is a method that allows you to forgo pots altogether. A blocking tool allows you to mold moist soil into blocks; as your plants grow, the roots fill out into the block and hold it together. The up-front cost of a blocking device can be a little bit high (~$35), but you will not need to buy pots again once you have the tool. 

Any time you reuse a pot from year to year, make sure to clean and sanitize it first to prevent the spread of pathogens. 

Water

One of the most common mistakes that new gardeners make is overwatering. No matter what method you use to water your seedlings (from above with a watering can, bottom watering into a tray), make sure you’re feeling your soil before you water.

It is important to maintain consistent moisture, so don’t wait until the soil is bone dry, but if it’s moist, wait until it’s just barely damp before watering again.

Signs that you’re overwatering might include crusty algal growth on the top of your soil, yellow leaves, or rotting seedlings. 

A way to maintain humidity while seeds sprout

While plants need plenty of airflow after they’ve fully germinated, there’s a short period of time when they require ample humidity to sprout.

You can achieve a mini-greenhouse effect by placing a plastic lid on your germination trays (you can often buy pre-made germination kits that include a lid). You can also take the DIY approach and use plastic wrap, a bowl, or another item to create a dome over your seeds.

For growers at a larger scale, there is a range of options for germination chambers from old refrigerators to covers that you can put around shelving units to hold in humidity. 

Once your seedlings have successfully germinated, you can move them out of this super humid environment. 

Seed starting inspiration

There is no perfect way to start your seedlings. For some inspiration, check out three videos that our team made last year from our seed starting setups at home: 

Author: Natalie Hoidal, Extension educator, vegetable crops and local foods

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