1. Overwatering. My kids recently experienced this one. They get so excited for starting their seeds and want to take the best care of them. It’s kind of like smothering a pet, you love it so much it hurts the pet. Don’t do that with your seeds. Wait until the soil is beginning to feel almost dry to water. And I mean almost dry, not completely dry. There should still be a bit of moisture in the soil. Your little seedling babies will be ok, I promise.
2. Not watering enough. A little stress on your seedlings will prepare them for the outdoors. However, you never want to wait so long to water that the seedlings start to shrivel up and die.
If it happens to you, don’t fret! Most plants will show they need water before they fully die off! Tomatoes are a good example. They will start to droop and look sad. If you catch it in time, water them ASAP and remove them from light and moving air. This will give the cells time to recover and soak up the water.
3. Not enough light. This is a huge and very common seed starting mistake! Invest in a shop light and use it for your seedlings. Do not use window light! It doesn’t provide enough light. It will weaken your seedlings right from the beginning and they will be leggy.
If your only starting a small amount of seeds, invest in 2 shop lights and hang them parallel to each other. It is worth the small investment. You want the lights on for about 16 hours per day. To start out, you don’t need special bulbs or grow lights. Regular fluorescent lights work just fine and will give the light your seedlings need.
However, make sure if you are using regular fluorescent shop lights that they hover just above your seedlings at all times. I’m talking an inch or less. You will need to adjust the lights as they grow.
4. Leaving the germination lid on after the seeds start to germinate. If you use a lid on your seed tray, take it off as soon as you see the first seedling pop up. The rest may not be above the soil surface yet but they won’t be far behind. If you leave the lid on you risk fungal diseases and increased risk of damping off, a common indoor fungal disease.
5. Too much fertilizer at planting. Having too much nitrogen in your soil at planting can impede germination of seeds. If you are using a bagged specially formulated seed starting mix, chances are it is safe to use. Do not use potting mix as this has more fertilizer and is not meant for seedlings. You can always add fertilizer later as needed.
6. Attempting to harden plants off too quickly. Hardening off your plants just means that you slowly introduce them to the outdoors a little bit at a time. This is another big mistake that happens to even experienced gardeners. Ahem…I may have done this this year by accident :)
The main issue is sun scald, the leaves of your delicate seedlings are not used to the brightness of the sun. The second issue with moving plant outside too fast is wind damage. They need to be moved outside slowly. 30 minutes the first day and moving up to an hour the next day. Add 30 minutes every day, incrementally, until they are ok being outside all day. Then have them spent the night outside for a few nights before planting.
It sounds easy but there is are some considerations. For example, if your first few days are overcast and by day three, your up to an hour and a half and leave them out there the full time. They may get burned because didn’t have full exposure to the sun on cloudy days.
The mistake I made this year was I fully hardened off my cabbages in an area of my garden that gets a little more shade than the rest. When I moved them to their final planting spot, some of them got very sunburned. I was surprised!
7. Planting old seeds. Old seeds often will have long germination times and low germination rates. While I have been known to do this occasionally because I can’t stand the thought of wasting seeds, I don’t recommend it. It’s very frustrating to wait forever for seeds to pop up, and then only get a few at best. Do yourself a favor and either test seeds for germination before planting or just buy new ones. How long a seed is viable for depends on what type of plant your growing.
8. Waiting Too Long to Pot up Seedlings. If your plants are showing signs of stress, getting crowded, or looking too big for the amount of soil, it’s time to move them to a larger container. Your plants will thank you! Mine always breathe a sigh of relief and then shoot up in growth like crazy. You never want to wait until the plants start to get root bound. Waiting too long will slow growth.
9. Sowing seed at the wrong depth. Check your seed packet to know what depth to plant. Some companies will not provide this information on their seed packets though. If that’s the case, Google it, don’t guess. Some plants need light to germinate and must be at the soil surface, others like to be deeply planted.
When in doubt, follow this rule of thumb. Use seed size as your guide. The smaller the seed the closer to the surface of the soil it should be sown. The opposite is also true, the bigger the seed the deeper it should be planted. For example, lettuce is a very small seed and should be surface sown or lightly covered. Peas are large seeds and need to be planted an inch deep.
10. Not having drainage holes. It’s so easy for plants to get waterlogged from too much water setting on the bottom of a seed tray without holes. Or let's say you move plants up to plastic recycled yogurt containers, poke a hole in the bottom of those! Then put a tray underneath to catch any extra water.
11. Sowing Seeds Indoors Too Early. We all get excited to get started with the gardening season! Sometimes, we can get a little too excited and start seeds too early. The biggest culprits with this that I see are tomatoes. Tomatoes planted too early can get huge and very leggy even under shop lights.
You think they won’t grow that big but just wait! They do! And I find it really makes for a weak plant in the end. I usually don’t start my tomatoes until four weeks before my last frost. I know that sounds so late to most gardeners but considering I don’t plant until 2 weeks after my last frost they spend almost 6 weeks in pots before being set free in garden soil.
Other plants may not get as tall or leggy but they will show signs of stress from being indoors too long.