Do Seeds Need Light or Dark to Germinate?

It’s seed starting time across much of the US and Canada, and many of us are trying to start our own seeds for the first time. While it can be a fairly simple process, there are a few things to know and understand in order to start your seeds and germinate them successfully. Since germination is the desired result, the goal is to create ideal circumstances for each seed to sprout. With that in mind, let’s address an often overlooked question: do seeds need light or dark to germinate? It’s more complex than a simple “yes/no” so let’s dig in and learn a bit about how light affects seed germination.

Gardzen Executive Summary:

· Some seeds do require light to germinate, while others germinate best in the dark.

· Regardless of whether germination is light or dark dependent, seeds still require the right combination of soil/starting medium, temperature, humidity, and watering in order to germinate and grow.

· Some popular garden seeds require light, some require darkness, so check the seed packet for more information and when in doubt ask an expert or look it up.

· It’s all about attention to detail and giving our seeds and plants what they need to thrive!

The Basics of Seed Germination

We’re using the word ‘germination’ a lot in this blog, so we should probably start by defining it. Put simply, germination is the process by which a seed develops into a viable plant, often called a seedling at that stage of its development. It’s important to remember that seeds aren’t inert, but rather living organisms in a dormant state. Inside the outer coating of a seed hides everything a baby plant needs to get started: an embryonic seedling, stored energy in the form of starches, and some enzymes waiting to kick off the growth process.

The key catalysts for seed germination are water and temperature. When it’s warm enough and the seed starts to hydrate, the enzymes inside activate the growth process. The seed softens, ready to release a baby plant. Enzymes convert starches into sugars that fuel the nascent growth. Then the radicle—that first small root—emerges from the seed, followed by the cotyledons—the very first leaves.

Seeds exhaust their on-board supplies of energy fairly easily so the new root starts to absorb nutrients and moisture directly while the leaves go looking for the sun. So, speaking of the sun: does light play a role in germination? Let’s take a further look.

How Light Affects Germination

As with soil, water, and temperature, different seeds require different things when it comes to light and germination. Some seeds, called ‘positive photoblastic seeds’ require light to start their germination process. Others, known as ‘negative photoblastic seeds’ germinate in the dark and light may actual interfere with their ability to start growth.

Positive photoblastic seeds require good light like bright sun or a good grow lamp in order to thrive. This needn’t ben an expensive grow lamp; a simple grow bulb in an unused desk lap will do fine to get things started. Just make sure that the entire seed tray is bathed in light so that things germinate evenly. Positive photoblastic germination works on some of the same processes that help full-grown plants respond to light. Photoreceptors in the seed sense the light and send signals which trigger the genes that start plant growth and tell the baby plant parts inside the seed that it’s time to start their development.

So what about dark germinating plants. A key takeaway here is that just “dark” isn’t enough; negative photoblastic germination still requires the right combination of air, water, humidity, and temperature along with an appropriate growth medium. Another key thing to remember is that negative photoblastic seeds may germinate in the dark, but they will need light when their leaves start to emerge. Set a reminder, mark your calendar, whatever it takes but check your dark-germinating seeds every day and don’t forget about them! Leggy seedlings can be difficult or impossible to fix, meaning you’ll have to start over.

Which Seeds Require Light to Germinate?

This is only a partial list, but some popular seeds/plants that require light to germinate include:

· Bellflower

· Butterfly Bush

· Celery

· Dill

· Lavender

· Lemon balm

· Lettuce

· Love-in-a-mist

· Mint

· Rosemary

· Salvias/sages

· Snapdragon

· Thyme

· Oregano

This is only a partial list, but as you can see it includes many smaller-seeded plants and culinary herbs. Check seed packets for full information about germination requirements.

Which Seeds Require Darkness to Germinate?

This is going to be a much longer list, but it’s also only a partial list. Again, check your seed packets, ask an expert, or contact your local cooperative extension for details about a particular plant.

· Asparagus

· Artichoke

· Basil

· Beets and Turnips

· Brassicas: Broccoli, Brussels Sprouts, Collards, Kale

·  Carrots

· Coriander/Cilantro

· Chives

· Corn

· Cucumbers and Melons

· Eggplant

· Mint

· Onions and Garlic

· Peas and Beans

· Peppers and Chilies, sweet or hot

· Radishes

· Squash and Pumpkin

· Tomatoes

As you’ve likely noticed, most popular garden veggies are dark-germinating plants. This is important to remember when setting up your seed trays and germination plans. Seeds planted at an appropriate depth in the soil or starting medium generally don’t require additional light protection, but you can always cover them or keep them in a dark place until the leaves emerge from the soil. Again—don’t forget about them and let them get leggy!

Light, Germination, and a Successful Garden

We hope this blog helps you understand the role that light and darkness play in seed germination, and which seeds or plants require light in order to germinate. No matter which seeds your starting, keeping them in appropriate conditions of water, temperature, and light and checking them regularly are important for their success. The distinction between light and dark germination helps us start our seeds successfully, but it’s also a good reminder that gardening is about attention to detail even for the smallest things.