If there’s any vocabulary in this article that stumps you, try taking a look at our handy Edible Gardening Glossary.
- Seed-starter soil
- Plant lights or regular lights
- Heated seed mat(s)
- Seed trays
- Humidity domes
- Soil blockers or containers with drainage holes
- Waterproof pen
When you’re planning to transplant your seedlings outdoors, your timing for starting them is very important. Things you will want to consider: How long will it take them to grow to transplant size? Will it be warm enough outside by then? Will the season last long enough for them to reach maturity after planting outside? These are all excellent questions, many of which you can find the answer to on the back of a seed packet, by doing some research, or by coming in to talk to our Kitchen Garden staff.
Find a Good Window
Even if you are providing supplemental light, there’s nothing like the real thing. Try to find a spot for your seed-starting in a bright window. Keep in mind that the direction the window faces makes a big difference! Window direction in order of desirability is: south, east, west, north.
Even though south-facing is the best light, keep an eye on seedlings in those windows. Sometimes the glass can cause the sun’s rays to be too harsh for sensitive seedlings at certain times of day. If this seems to be the case, move them back a few feet or add a sheer curtain to solve the problem.
Keep an eye on west-facing windows for the same reason. Sometimes afternoon light can be a bit strong, supplemental light might be needed.
Morning sun in an east-facing window should work well, but supplemental light will probably be needed.
With north-facing windows you will certainly need supplemental light, but the seedlings will still appreciate the addition of indirect sunlight.
If using lights, it’s best to place them just a few inches above your seedlings. Just watch to make sure they aren’t giving off too much heat. Regular lightbulbs will help, but plant lights are even better.
If you notice that seedlings are leaning, rotate them so they grow evenly.
The reason starting with a specific seed-starting soil is a best practice is because it is guaranteed to be sterile--free from soil-borne fungus, bacteria, insects and weed seeds. This gives your seedlings the very best chance at a healthy start. It also has excellent drainage which helps keep seedlings from getting oversaturated.
One mistake many beginners make is to plant seeds in too-dry soil, then add water, expecting that the soil will uniformly disperse the water throughout. Sadly, it doesn’t work that way! Instead, the water will pool on the surface and often run down the side of the container, never even reaching the newly-planted seed!
How to fix this?
Start your seed planting process by pre-moistening the soil. To do this, put the soil you are going to use (or part of it) in a container with extra room for mixing. Don’t add too much water at once: gently sprinkle the surface of the soil with water, mix it in, then repeat the process until the soil is uniformly moist. You want it to be moist, but not wet. Roots need a combination of moisture and air to thrive; make sure not to overdo it to the point of oversaturation. Now the soil is ready for seeds!
If you’re using containers, just fill them with your pre-moistened soil and tamp down a bit… but not too much! Drainage holes are very important so that soil doesn’t stay oversaturated.
Watering from the bottom is usually a better idea than watering from the top. Seed starting trays makes this easy. If you water from the bottom, the soil will act as a sponge lifting the water to the seeds. This encourages roots to grow downward. Watering from the top can cause soil compaction and lead to plants developing roots that are weak and shallow. It can also cause oversaturation around the seed or seedling.
Seeds need to be kept moist in order to germinate. One way to greatly increase your chances of success is to cover your seeds with a humidity dome until they’ve sprouted. Make sure there is also some air flow, without circulation seedlings can suffer from fungus and mold issues. Some seed-starting trays come with a dome.
Depending on what you are growing, some seeds require a specific minimum soil temperature before they will germinate. This is a brilliant adaptation to give the resulting plant the best chance of success when it is growing without our help. Even though they don’t all require it, most edible plant seeds will appreciate it and will be easier to start when warm.
If seeds are sitting in a warm window, they may be warm enough. Soil temperatures are listed on the back of seed packets. Fortunately, if you can't get the warm enough with the sun or lights, you can use a seed-heating mat under your tray of soil.
Take a look at the back of your seed packet to see how deep they would like to be planted. Generally speaking, the bigger the seed the deeper you plant it. Most seeds need darkness to germinate, but others need light and are just left on the surface of the soil. Make sure to find out what's best for your particular seeds.
Make sure to label your planted seeds. Many seedlings and young plants look very similar to each other. You might think you will be able to remember, but you will thank yourself later if you take the time to make clear, waterproof labels.
It’s also a great idea to draw a picture in your gardening journal with the plant names included as a backup in case a tag is lost.
Next Step... Potting Up
Think ahead… if your seedlings start to outgrow their accommodations, but it’s still too cold to go outside, you may need to give them more space to grow before transplanting. A four inch pot is usually a good size to pot them up to.