Tips for Starting Broccoli & other Brassicas Indoors from Seed

on Mar 19, 2015, Updated Oct 28, 2023

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It’s time RIGHT NOW to start broccoli and other brassicas indoors from seed in my gardening zone, zone 5. Ideally, brassica seeds (broccoli, cabbage, cauliflower, and Brussels sprouts) are started 6-8 weeks before the last frost, and with an average last frost date of May 15, the time is now! Kale and Kohlrabi are also brassicas, but I have found them to perform better with a direct seed into the garden than to start them indoors from seed.

Tips for Starting Broccoli & other Brassicas Indoors from Seed

To start brassicas, the following supplies are helpful:

Seeds (these are my favorite places to order garden seeds)

Coconut coir pellets (I’m trying my luck with these pellets this year, but in past years I have used all kinds of different soil and pots.)

Lidded container (to create a mini reenhouse). I reused my seed starting containers from last year.

Heating pad (Useful for helping the seeds to germinate.)

Grow light (I use T-8 Grow Fluorescent bulbs like these.)

Shelf or somewhere safe to keep them the seedlings away from kids and animals.

The Technique

Starting the seeds is pretty easy, you guys. Here’s what you do:

1. Prepare your pots and soil per ingredient directions. If you’re using pellets like I did, soak them in warm water to make them expand.

2. Then, put 1-2 seeds in each pot and push down a bit into the dirt, if you can. This year, I am trying my luck at Calabrese Broccoli {my favorite variety to grow}, Romanesco {tried to grow this last year unsuccessfully}, broccoli rabe, regular ole hybrid broccoli, red cabbage, green cabbage, bok choy. I have never had good luck with cauliflower so I think I’m giving up. I’ll probably buy Brussel Sprout starts since I forgot to order seeds! DOH!!!

3. Make sure to label the pots somehow, as they all look very similar – especially different varieties of the same type of plant – different types of broccoli, for instance. All I did to label was write on masking tape and tape the inside of the greenhouse. As the seedlings grow, I will have to label each pot individually, but for now, since all of my seedlings are in a straight line per type, it works just to label the inside of the greenhouse. {I say this now, but watch my kids rearrange everything tomorrow and screw me!}

4. Put your pots in the greenhouse and put on the lid. I put my greenhouse on the heating pad and turn it on.

5. Once the seeds have germinated, I turn of the heating pad, and turn on the lights – as close to the seedlings as possible to prevent the seedlings from becoming leggy.

6. Remember to water often and keep track of when they germinate, etc!

7. Brassica seedlings can be transplanted into the garden 2-3 weeks before the first frost, but make sure you harden them off properly before leaving them outside long term.

That’s it, you guys! What steps do you do that I didn’t mention? Stay tuned for more tips on how to prevent leggy brassicas! I have found them to be a tad tricky…