Growing Roselle from Seed

Photos by Peggy McDonald

Peggy McDonald, who we call the Roselle Queen, grows hundreds of Roselle plants for the Master Gardener plant sale held at the Leon Count6 UF/IFAS Extension on Paul Russell Road in Tallahassee each May. (scheduled for May 11 this year—save the date!). They are always a sellout. 

It’s time for Peggy to start growing this year’s crop and she’s recruited a dozen of her fellow Master Gardeners to help her. Typically Roselle isn’t planted until very warm weather in late April or May, so in order to have seedlings ready for the plant sale in May, it is necessary to force them to grow earlier.

Peggy has shared her instructions for growing Roselle seedlings. You can do it too. Roselle is an annual in our area so seeds need to be planted or seedlings grown each spring.

Peggy’s instructions:

A long hot summer is perfect for growing the Tropical Roselle plant.   I force the plants to sprout earlier so we have sizable plants to sell.   Otherwise we would have very small two inch plants. Here are a few tips for success in starting it and forcing it to grow earlier in the year. .

I start my seedlings for the May Plant Sale inside the house, under lights and with a seedling heating mat. They like it 80 degrees to germinate and my house is not that warm in March.

Planting schedule:

Start two months before the sale, this year that is March 11, 2024. I use damp ProMix HP Mycorrhizae seed starting mix. Another favorite mix is "Coast of Maine Organic Seed Starter". Any sterile seed starting mix will do,  The seeds do not need light to germinate.  Plant 1/8”-1/4” deep. I put plastic wrap over my two 72 cell trays and check to see they stay moist. I use my grow lights lowered to about 2" over the flats and they stay on 14-16 hours a day. 

The heat mat is set at 80 degrees under the trays and is always on, do not plug it into the timer. Remove plastic once the first seedling sprouts. The heat mat can be turned off after germination but leave the grow lights on. 

Roselle—14 days

I start setting the seedling trays outside when they are only one inch tall when the sun is out and it is 50 degrees or warmer. Place the flats away from drafts. Start with 15 minutes increase every two days. When you see true leaves, start with 1/4 strength liquid fertilizer like Neptune Harvest (2-4-2) weekly until up potted. This is not necessary with Coast of Maine soil, as it has fertilizer.

Ready to up pot

Check to see when the seedling roots have filled the cells, this will vary with the size of your seed trays. Usually by two weeks I up pot the starts to gallon pots with the Dirt Baggers bark soil (any good potting mix) and a half tablespoon of Osmocote. No more fertilizer is needed. Check the weather forecast for future warm temps above 50 degrees before you leave them outside overnight. Move to full sun gradually, an hour a day, then two hours, etc.

Roselle—23 days.  After up potting

Most of April they are in the garden for hardening. At 4 wks old when they are 4"-5" tall, pinch the leader out of the seedlings to encourage branching. I put the pots in a protected area between my raised vegetable beds. To keep racoons and squirrels out, I block off each end of the path. Also put dried leaves on top of the soil, which seems to keep the squirrels out of the fresh soil. Note: if temps fall below 50 degrees I move them all to the garage or cover with spun lightweight frost cloths.

At 7 weeks—they are ready at this age. Pull one out of its pot to see how the roots look. If the pots are full of roots you will have to be sure to water the pots once a day for the last week. 

Roselle—60 days.  Ready for new homes. 

At the Plant sale they are 8 weeks old, hardened off and 2 feet tall, ready for in ground planting. These plants grow so robustly, there is no set back or stunting to the plants when you start them this way. They still grow up to seven feet tall and six feet wide and should be staked with a sturdy t-post.

Seed collecting:

You wait for the calyx seed pods you leave on the bush to dry out and start to split open usually the end of October. The seed pods will turn light brown and the calyx will be dark red and shriveled. It usually takes a month or so, but I have found this provides the best germination rates. The kidney shaped seeds become plump and brown, discard light tan seeds. Each seed pod has from 25-30 seeds. Pick the pods before they spill their seeds and spread the seed out on paper for at least two weeks to dry.

So there you have it, everything but processing and enjoying the 10-11 gallons of fruit from each seven foot plant.  Check out the Vegheadz blog for Roselle recipes.  (Search Roselle in the right sidebar search box.)

Seedling heat mat

A note about heat mats:  There are lots of brands on Amazon you can use.

I use a standard size 10" x 20" to fit under a standard 1020 tray. When looking for one on Amazon the most important part is the thermostat to regulate the temperature. It has a probe you insert into the soil in your seed tray so you get a temp reading of the seedling roots, not the temp under the 1020 tray. Mine is 4 years old, no problems yet. Water resistant, the mat should not be submerged in water but takes daily misting just fine. I use my mat all the time to start herbs and difficult pepper seeds.

Also in the picture is a handy moisture meter I like, it came with two in the package. No batteries but I can insert the probe and get the moisture level all the way down to the bottom of my pots. Good for houseplants you are overwintering inside.