Seedlings need to be treated like delicate babies. They are easily killed off unless they get ideal conditions for their growth. Baby animals need warmth, food, and protection. Seedlings are the same. Most seeds in the wild die - only a small fraction that have close to ideal conditions will survive. So, because we want most of our seedlings to survive, we try to give them close to ideal conditions.
This article covers the basic needs of most food and flower seeds commonly grown in gardens.
Step by step growing instructions
Create a good seed mix. Seeds are delicate and must have light, fluffy soil that holds water and provides air and space to roots. If your seedlings are not growing fast, often it is because the soil mix is too heavy. Delicate baby roots can’t get through the soil.
Our mix is 2 parts coconut coir (bought from hydroponics shops), 1 part screened compost (must get large particles out), and 1 part vermiculite. We recycle this soil, especially the vermiculite. We have used 2 parts coir and 1 part compost with success, but adding the vermiculite gives us more success. There are other mixes out there. We use this one for a variety of reasons - it works but so do many others that provide the basics named above. If we plan on keeping seedlings in trays for a while before transplanting, we add a small bit of organic fertilizer and/or rock minerals to the mix. They don’t need much! Note, there are many versions of mixes that work well; you can find other recipes on the internet - this is the one we happen to use.
Get the mix into trays. We use soil blocks, which create an easy way to transplant the seedlings with minimum root disturbance, but other methods work fine as well (Johnny’s seed carries them ). A soil block reduces transplant shock and makes seedlings easier to plant, but it’s more work up front. You can also plant seeds directly into a 10X10 tray filled with soil mix, or individual containers. People are successful with all of these methods. https://www.johnnyseeds.com/tools-supplies/seed-starting-supplies/soil-block-makers/hand-held-4-soil-blocker-7862.html?cgid=soil-block-makers#start=1).
Add seeds. Once you have the soil prepared, put from 1-4 seeds per hole. Not all will germinate. Note that each seed has special needs. Lettuce seeds need light to germinate so should rest on the surface or slightly below. Other small seeds should be planted in shallow pits and covered with a bit of soil. Larger seeds can be buried more deeply, anywhere from ¼-1 inch deep depending on the seed. Usually they are less fussy than small seeds.
Water. Seeds must be kept moist until they are germinated. That usually means watering twice per day minimum and not just a light mist, but enough to ensure the soil stays moist. Use a light garden spray or mist to water them - if you disturb them too much, they will move around, germination can suffer. If in soil blocks or a tray, they can all end up lumped together with a hard spray that moves the soil around.
Reduce watering. Once the seedlings are up, the soil must be allowed to dry out on the top ¼” or plants are subject to root rot. But they can’t dry out too much or their delicate roots will die. This is a tricky period where you need to pay attention to them every day. They may need watering every day, or every other day depending on temperature, humidity, wind, etc. After they get a bit bigger you can pick out extra seedlings per hole - you should have only one per hole, and choose the strongest.
They will need regular water until they are big enough to plant unless they are very drought tolerant. The process to get them ready for transplant generally takes 4-6 weeks depending on the seed and how big you want the transplant to be.
Needs. During this period, seedlings need sufficient sunlight and air movement. Wind actually strengthens and thickens their stems. Sufficient sunlight will allow them to grow robust, healthy leaves, roots and stem. If they have enough of both, plus water and nutrition, they should be growing thick stems and healthy, large leaves. Temperature can also affect them. If too hot or cold, their growth will be inhibited to some degree.
Transplant. Seedlings are ready to transplant when they have at least two sets of leaves. The first leaf will look different than the second leaf. They should be strong looking and not spindly. They will have a more challenging environment to survive in, so they need to be robust and strong enough. Prepare a hole for the seedlings 2-3 times the size of the rootball. Add some compost and garden soil. Disturbing the roots as little as possible, gently place the seedling in the hole and spread compost around it. Water it in gently, and continue to water it 2X per week or as needed until the roots are established. Most veggies or flowers, once established, can take watering 1X per week unless it is very hot, windy or dry.
Protect soil. You will want to cover the soil around your seedling with wood chips or other mulch, but never put wood chips, straw or other mulch up against the stem of the seedling. Always leave a few inches of empty soil around the plant. Seedlings can easily get root rot if anything is touching the stem.This is true of most plants - wood chips are a very good vector for root rot if they touch the stem or trunk of the plant where it meets the earth.
Feed. If your plant’s leaves do not look healthy, are yellow or crinkled or spotted, etc, feed your plant organic manure, or an organic fertilizer like Espoma or Azomite minerals. Some people give their plants a lot of food and get great yields. We like to let our plants tell us when they need something and give them food only then. If your beds are set up nicely, you may not need to feed them at all during that season.
What can go wrong?
- Soil too heavy - seedlings will stay small and stunted - for months! This can also happen if it is too hot or cold.
- Not enough light - seedlings will get very leggy with thin, weak stems and small leaves. Enough light means large leaves, strong and compact stems.
- Bad germination - not enough water, temperature too high or low, or seeds too old. There are other reasons for some seeds specifically but those are the main reasons. Note - some seeds take weeks or months to germinate! Banana seeds take 6 months. That’s why we just get banana babies from the mother plant. We do not have six months of patience!
- Too much water - the stem right where the soil is will get very thin, usually black, and the seedling will fall over and die. Root rot.
- Too little water - the seedling will not come up at all, will be weak if it does, and eventually die.
- Not enough air flow - Seedlings will have thin stems, be leggy and weak, or get fungus and die. Seedlings thrive on some wind - it strengthens their stems like jogging strengthens your leg muscles. We use fans in our greenhouse for that reason.
- Extreme temperatures - Most seedlings will germinate somewhere between 50-85F. Some are more picky than others and have narrower ranges. If temperature is too high or low, you get poor germination. Once seedlings come up, they can handle greater temperature swings, but if it’s too hot or cold, it will inhibit their growth. We start seeds indoors under a T5 light, and move them out when they get their second leaf. Or we start in the greenhouse.
Happy planting!!