What should you avoid when you're starting seeds indoors?

Starting garden plants from seeds indoors in a marijuana grow tent can be an enjoyable project for any gardener. It's a relatively inexpensive way to grow a wide variety of plants. Many garden favorites are found in a greater variety of colors, sizes and growth habits as seeds, rather than as started plants.

There are many benefits to starting seeds indoors rather than waiting to plant outdoors. The main reason is to get an early start on the gardening season.

In colder climates with short growing seasons, starting seeds indoors allows you to gain a few precious weeks of growing time, which can really make a difference when frost looms in the fall. Slow-growing crops such as tomatoes may not even have enough time to reach maturity if they are planted outdoors.

In warmer regions, starting seeds indoors can allow you to get in an extra round of crops (especially cool-weather crops) before the heat of summer stifles growth. 

If you want to grow a lot of plants, buying packs of seeds is usually cheaper than buying individual seedlings from the nursery.

While some nursery plants are grown really nicely, others are poor quality. When you plant your own seeds, you have control over the way the young plant is raised. This may be especially important if you are an organic gardener.

Finally, there isn’t always a great selection of plants at local nurseries. When you plant from seed, you have a much wider choice of varieties, tastes, and textures—and you can experiment with new ones, too!

• Starting seeds at the wrong time

Many plants do not tolerate cold temperatures, and exposing them to chilly air or cold soil will stress them out. Chas Gill, who runs the Kennebec Flower Farm, agrees that one of the biggest mistakes people make when starting seeds is starting the seeds too early. Stressed-out plants are more susceptible to pests and disease. Most plants are ready to go outside four to six weeks after you start the seeds.

• Not reading seed packages

There is a lot of valuable information on a seed package! The ideal time to start or plant this particular variety, how deep to sow seeds, the recommended plant spacing, and more. The germination rate gives you an idea of how many seeds you should expect to sprout. If that number is below 75%, sow a few extra seeds as added insurance. If it is nice and high, just a few per hole or container will do.

It is important to read seed packages even if you think you’re familiar with that type of vegetable. For example, different varieties of the same veggie (say, 3 types of onions) may have varying requirements or instructions! 

• Using the wrong soil

Another common seed starting mistake that new gardeners make is using just any old soil to start their seeds in. Old soil from the garden or yard may contain and introduce diseases or pests to your new seedlings. On the other hand, some bagged potting soil is too dense, and has a less-than-ideal texture or drainage for seed starting. In the wrong soil, seedlings may grow less vigorously – or fail to sprout at all!

Always start with fresh, clean, bagged soil that is specifically made for starting seeds, like this one. It will have the right light and fluffy texture to promote germination, and allow the tiny hair-like new roots to grow with ease. Bagged seed starting mix will also be free of potential pests or disease. 

However, because it is so light and mild, seedlings won’t be happy for an extended period of time in seed starting soil alone. Sometimes we add just a small amount of richer potting soil and worm castings (no more than 30 % of the overall mix) to our seed starting soil. Or, the seedlings will eventually need to be fed or transplanted to get the nutrition they need. Be sure to keep reading to see the fertilizing and potting up tips below!

• Not providing warmth

For most types of veggies and seeds, the optimum soil temperature range for seeds to germinate (aka sprout) is around 70 to 80°F. At the right temperature, seeds sprout readily – and move on to their next stages of growth more quickly too! Without adequate warmth, they can be sluggish or potentially not sprout at all. Note that a handful of plants do prefer cooler soil to germinate, such as onions, lettuce, and peas. They like it around 50-60 degrees. 

When you are starting seeds indoors, keep your seed trays in a warm location of your house. This could include the top of a refrigerator or tall shelf (heat rises!) or next to a sunny window, but not one that is cold and drafty. Sometimes those spots aren’t quite warm enough however, especially during the winter months.

A heat mat is a very handy gardening tool to have. In combination with a thermostat, a seedling heat mat can consistently keep the soil temperature in the perfect range. Ours has a probe that stays in the soil, and only turns on when the soil needs heat. That means that as things naturally heats up during the daytime, the heat mat turns off. As the temperature drops in the evening, it kicks back on. But do not heat seeds over 95°F! This can sterilize and kill them.  

Another way to help keep seeds warm (and damp!) during germination is to cover the seed containers. Humidity domes placed over the seedling trays trap in heat and moisture to help aid in rapid germination. But as soon as they sprout, it is best to uncover those babies – because they need light! 

• Insufficient light

Seedlings need a lot of light to grow into sturdy, healthy plants. No matter what anyone tells you, chances are that you do not have enough natural light in your home to grow robust seedlings. Even a south-facing window usually will not do. You can, however, use artificial light to achieve the right amount of light required by seedlings. To do so, obtain full spectrum LED grow lights explicitly designed for plants. Or, for a more economical solution, purchase large fluorescent shop lights outfitted with one warm bulb and one cool bulb.

Suspend the lights from chains so that you can raise the lights higher as the seedlings grow. Keep the lights as close to the seedlings as possible without touching them (2 to 3 inches). When seedlings first appear, keep the lights turned on for 12 to 16 hours per day. To reduce your hands-on time, use a timer to turn the lights on and off automatically. By the way, ECO Farm grow light can be your great choice.

• Watering too much (or too little)

The amount of water you supply can make or break seedling growth. Watering is one of the most challenging aspects of seed starting. Because seedlings are so delicate, there is very little room for error when it comes to watering. You must keep the sterile seed-starting medium damp but not wet.

To increase your chances of getting it right, here are a few things you can do:

1. Create a mini-greenhouse to keep soil moist: cover the container with plastic until the seeds germinate.


2. Water from the bottom to enable the seedlings to soak up water through the container drainage holes. There is less chance of over-watering when you use this approach. Add water slowly for 10 to 30 minutes, and use your finger to touch the top of the soil to ensure that moisture has reached the top of the container.


3. Check soil moisture at least once a day.


4. Buy a self-watering, seed-starting system.

• Fertilizing incorrectly

When seeds first sprout, they don’t need any fertilizer at all! That’s because seeds are amazing. The seed itself contains all the food and nutrients that its seedling needs for a few weeks after sprouting. If seedlings are fertilized too soon, it could harm or even kill them.

On the other hand, if seedlings are left without any fertilizer for a month or two after sprouting, they will be starving for nutrients and grow far less robustly than they could be. This is especially true if they’re not potted up and are left in their original seed starting soil. Finally, using too strong or the wrong type of fertilizer can burn or shock seedlings, even if it is applied at the “right” time. 

Leave your seedlings alone for the first few weeks. I mean, give them water and light and love of course… but don’t fertilize them! The best time to start feeding seedlings is after the first couple sets of “true leaves” appear. True leaves are the ones that come after the very first two sprouts (often heart-shaped), called cotyledon.

We like to feed our seedlings using a dilute seaweed extract. It is gentle, sustainable, and effective! As long as you mix it according to the instructions, it is virtually impossible to burn or shock seedlings with seaweed or kelp fertilizer. To do so, we simply mix it with water and pour it into the trays below the seedling containers (watering from below) in place of their routine water. Repeat every other week. See this article all about feeding seedlings with seaweed extract for more details. 

Another way to feed seedlings is to pot them up into a larger containers with richer soil, explained next.

• Not thinning or potting up

Crowded, cramped seedlings are not happy seedlings. When they’re left un-thinned, those several sprouts will compete for nutrients, root space, and water. Furthermore, crowded seedlings get less air circulation and may lead to disease or damping off. They may also shade each other out and not get the best light, leading to leggy seedlings. 

Even once they are thinned out, seedlings will not be healthy if they’re left in small containers for too long. Their roots will run out of space to grow and wind around themselves, becoming “root bound”. Plants that are allowed to become root bound are often stunted long-term. Meaning, even once they’re potted up or transplanted into a garden bed, they will not grow as large and healthy as they could have. They will not reach their full potential!

Different gardeners have varying methods and preferences for thinning seedlings. Some like to pluck and pull out the “unwanted” ones. Personally, we prefer to trim out the excess sprouts with little pruning snips, reducing the risk of disrupting the keeper. We start this process around the same time we start feeding seedlings, just a few weeks after sprouting. By then, we can determine who the strongest, healthiest looking sprout is to keep. The sooner, the better!

• Skipping the hardening off process

Imagine this: you’ve dedicated your love, effort, and time to raising healthy little seedlings. You’ve even avoided many or all of common seed starting mistakes you’ve learned here today. It is finally time for your baby seedlings to move out of the house into the big world waiting for them outside! You plant them in your garden. The sun shines down on them, they sway in the wind, they’re dewy with mist… Everything is looking good. And then they die. 

Did you forget to harden your seedlings off? Without a proper “hardening off” process, seedlings that were raised indoors (or in another sheltered environment, such as a greenhouse) are not ready for the conditions of the great outdoors. They are susceptible to sunburn, snapping in the wind or rain, and general shock.

“Hardening off” is the process of slowly introducing seedlings to conditions that mimic the great outdoors, and also gradually bringing them outside to become more hardy. This prepares them to be planted outside in a smooth, healthy, stress-free transition.

Start early! Just a couple of weeks after sprouting, we introduce movement and airflow to mimic wind by using an oscillating fan nearby. If you are using a heat mat, you should start to slowly reduce the temperature and time it is used as it gets closer to planting time.

Finally, a week or two before actually planting them out in the garden, seedlings should be brought outside little by little to get exposure to direct sun, wind, and other outdoor conditions. Start with just a couple hours per day in a shady location. Then, gradually increase the time and sun exposure over the course of a week. Here is a step-by-step guide to hardening off seedlings.

This is the secret ingredient to successful seed-starting: you should check your seeds daily. Check to see if the seeds have sprouted so you can remove the cover when it's time and make sure the seedlings have light; check to make sure they stay properly moist but not too wet; check your reservoir if you have a self-watering kit; check the seedlings’ growth and raise the lights so they stay 3-4” above the plants; and check to make sure the grow lights weeds and timer haven't malfunctioned. If you are starting a few seeds on the windowsill, turn the plants every day so they don't bend toward the light.

As you plan your seed starting, factor in your convenience and habits. Will you really remember to check seeds in the basement daily? It might be wiser to start seeds in the guest room or kitchen where they will be handier, even if you have space for fewer seedlings.

As your seedlings grow, watch the weather. Although a few crops can go outside earlier (refer to the seed packet), most should stay indoors until after the last frost date for your area has passed and your soil has warmed. If your area is having a cold spring, hold off. Gardeners are always eager, but many a carefully nurtured tomato seedling has been killed by a May frost or simply slowed down by cold soil. Protect your investment of time and attention by planting later rather than earlier.

Finally, introduce your plants to the sun gradually, a process called "hardening off". Expose them to sunlight for one hour more each day for a week. During this time bring them to a protected location outside when they are not in the sunlight. If there will be a frost at night, bring them inside. After a week or so, they will have acclimated to the outdoors and will be ready to transplant.