When Should I Plant Coleus From Seed? Does Variety Matter?

Are you thinking of planting some coleus by seed this season but aren't sure when to start planting? Maybe you aren't sure if the coleus variety you've chosen impacts when it should be planted? In this article, certified master gardener and coleus enthusiast Laura Elsner examines when you should be planting coleus, and if the variety you've chosen makes any difference.

Grow Coleus From Seed

I love ways to cut corners from the sometimes expensive endeavor of gardening. Seed starting is definitely one of the best ways to save money. However, not all plants are worth starting from seed. Some need periods of cold, some need to have their outer coating nicked (this is called stratification), and some won’t produce blossoms, or fruit, for years and years. So I think as home gardeners, with limited time and space, it is important to choose which plants you will start from seed vs the ones that should be purchased or divided. 

Coleus are definitely on my list of ones to seed. They only need to be started from seed once, then you will have an endless supply of cuttings to root if you want. They are easy to start from seed and will produce large beautiful coleus plants early on in the season.

In this article, I will aim to explain when, how, and which kinds of coleus you can and should be starting from seed. So grab your containers, soilless mix, and seeds, and let’s get started. 

The Short Answer

Start planting coleus by seed about 8-12 weeks before the last frost in your hardiness zone. You should start them off indoors, in small containers. Variety doesn’t matter as much around planting and growth, but it will matter with regards to how you plan to use the plant. For instance, if you plan to grow your coleus in a sunny area, you’ll need to pick a sun-friendly variety to plant as seed.

When to Start Coleus Seed 

Bright Green and Purple Seedlings
The best time to start your coleus seeds is 8-12 weeks before the last frost.

Coleus takes a bit of time to germinate, and it can take a long time to grow into little coleus plants. Therefore it does need to be started early. 8-12 weeks before the last frost in your area. It’s a quick search to find out the last frost date in your area if you don’t know it. Then count backward 8-12 weeks.

I know it’s a month difference, but it’s nice having a large window so you’re not feeling too much pressure to get on seed starting. The earlier you start, the larger your coleus plants will be when you plant them. But, smaller plants will catch up quickly, so don’t think it’s not worth it if you only have 8 weeks. 

I will say that starting seeds extra early is not usually a great idea. Zucchini, for instance, don’t transplant well and seeds I’ve direct sowed in the garden perform better than ones I start early. But coleus is an exception to this. I think this because technically coleus can be grown as a houseplant. So whenever you are ready to start your coleus is fine. Just don’t bring it outside until all risk of frost has gone.  

Also, be prepared to look after a coleus seedling and plant. They do require quite a bit of watering, they go from droopy and needing water to dead in a short period of time. But technically you never have to bring your coleus outside; they make great houseplants. No matter how large your coleus plant has grown if it is going outside make sure you harden it off (more info on that process below). 

Choosing a Variety  

Bright Colorful Plants in Nursery
There are so many varieties of coleus to choose from, it can be hard to decide on just one!

First things first. You will go online searching for seeds and you will come across fantastic coleus of blue and electric purple. These are not real. I don’t know why this isn’t regulated. These too-good-to-be-true seeds are found on websites all the time. I never buy seeds from companies that ship them overseas, I prefer finding local seed sellers whenever possible. 

Another thing about coleus seed is a lot of coleus varieties won’t come true to their parent plant. Since most coleus is now grown from cuttings, their seed will not produce their exact match. A cutting is a plant’s clone. But a seed is a plant’s child, which as we know is similar, but not exactly like its parent.

Instead of collecting seeds from your coleus, just grab cuttings if you want to propagate them (I go into detail on how to propagate coleus cuttings in the how to grow guide). 

Buying Seeds  

Red and Green Plant Growing in a Garden
Coleus seeds can be found online, in nurseries, and in plant shops.

So, what seed to get? My best advice is to find seeds at the store from a reputable seed seller. You are likely to find Wizard Mix, Fairway Mix, or Carefree Mix. These are a mixture of various coleus from their series. It will be a grab bag of varieties.

I like mixed coleus together, but if you’re looking for a specific variety in the mix, plant them all and then as the true leaves appear, choose only the ones you want and separate them out.

You can find just one variety in seed packs, you’ll need to search around. Always buy coleus seeds from a reputable seed website or store. Also look for a named variety, like ‘Chocolate Covered Cherry’ or Electric Lime‘, do some research, and make sure you are going to get what you want. 

How Are You Using Your Coleus? 
Colorful Seedling Plants in Starter Tray
Knowing how you plan to use your coleus can help decide on a variety.

The next important question to ask yourself is how are you going to be using your coleus? Depending on how you plan to use the plant, there’s going to be some considerations to make before picking a coleus variety to plant from seed. 

Will it be a focal point in a pot?

Then you will want to choose a larger variety that has some height and can show off in a pot. This will allow them to get a bit larger, with big and beautifully colored leaves.

Will it be for a border in a garden?

You will need a large amount of a low-growing variety for this. The good news is that most coleus is low growing, just make sure you have enough seed before you start planting.

Do you want it to be draping downwards?

There are trailing varieties that will spill out of pots and off ledges. Ensuring you have the right variety to accentuate the leaves dripping over the edge of a garden fixture will enhance the looks of the plant.

Think about how you will be using your coleus and purchase seeds accordingly. The good news is that there are many different seed retailers, and there are many options because there are so many cultivars available.

Planting Coleus Seeds

When planting via seeds, there’s a few important factors to consider. You want to have the right soil, indoor care if planting from starts, and also make sure you harden off at the appropriate time. Let’s take a little deeper look at planting from seeds.

Soil

Gardener Adding Potting Soil to Seed Starter Tray
Using good-quality potting soil is the first and most important step to grow coleus from seed.

Start with your seeds and some soilless seed starting mix. This is easy to find at garden centers. However, if you don’t want to use it, a good quality potting soil should be fine.

Grab some containers. You can purchase really nice seed starting containers that come with dome lids. But you can also use old yogurt containers, plastic take-out containers, berry containers, etc. Just make sure you poke holes in the bottom so they have drainage.  

Make sure your soil is evenly moist. I do this like I’m kneading dough. I add soil to a container and a bit of water and knead it until it’s a nice spongey, but not dripping wet, consistency. 

Put this soil into your containers. Now sprinkle your coleus seeds evenly over the soil. Coleus seed is tiny, you might accidentally put too many on the soil, don’t worry, you can thin them out later. You can purchase a little plastic device at garden centers that you put your seed into and it will make them put out slowly if you like. 

Germination

Bright Green Plants in Small Tray in the Sun
Germination can take a few weeks, but the color will eventually start to show!

Coleus seed needs light to germinate, so just mix them into the soil gently, no need to cover them fully with soil. Put a clear plastic lid on top of the container (this is why berry containers work great). 

Then place the containers somewhere warm to germinate. You can purchase seed mats for this purpose. Or just find the warm spots in your house, like on top of the fridge, or on the counter above the dishwasher.

Don’t place them on heat registers. Bottom heat will help them germinate faster, if this isn’t something you can do, they’ll be ok, maybe a bit slower to germinate. Don’t put them anywhere cold, like by a window. 

Seedling Care

Bright Red and Green Plants in Pots
Coleus seedlings will need daily checking to ensure healthy growth from the start.

Set a timer and check the seedling daily. Make sure they don’t dry out or get too wet and moldy. If they’re dry, spray lightly with a spray bottle. If they are too wet, leave the lid off for a day. 

The seedlings will emerge in around 7-14 days of planting. Once they emerge, bring them to a sunny window or under a grow light. 

If the seedlings look spindly or ‘leggy’ and are reaching for the light source, they need more light. Put the grow light closer, or get them into a sunnier window. 

The first leaves of your coleus seedlings will look like generic plant leaves. These are the plant’s cotyledons. The next set they grow is their true leaves and will look like your coleus variety.  

Once more true leaves form you can pinch them back so they grow bushier. If you have too many seedlings bunched together you may need to thin them out. I usually just pinch the ones I don’t want as close to the soil line as I can. Pulling them by the root can disturb the roots of the ones nearby that you want to keep. 

Keep watering them as they grow bigger and bigger. I will also brush them with my hands a few times a day, or have a fan on a low setting to blow them around and strengthen their stems. 

Hardening Off 

Bright Red Seedings in Small Starter Pots Hardening Off Outside
It is very important to harden off your coleus plants before planting them in their new outdoor home.

So you’ve gone through 8-12 weeks of nurturing these plants and the last frost date has passed and you put them out in the garden. They are dead by the end of the day. I’ve had this happen in my early days of gardening. It is the worst. You need to go through a process called hardening off in order to get your seedlings ready to face the elements. 

All your seedlings need to go through this process before they can be planted in the garden. It takes a few days. Do not skip this step. Start by taking the seedlings and placing them in a shady area that is protected from the wind. Leave them there for 2-3 hours then bring them in.

The next day, add a few more hours and maybe some dappled sun. Bring them in. The next day, leave them in the dappled sun/shade for most of the day and leave them overnight. Then leave them out all day and night.

If at any point they start to go completely limp (they will pout and droop a bit that’s normal) bring them inside and start again with shade when they perk up. Also, make sure they are watered throughout this entire process. Now your coleus are ready to go out to the garden.  

Final Thoughts 

Coleus are easy to grow from seed, they germinate easily and grow into plants that can go into the garden. However, if possible I would recommend using cuttings from existing coleus plants. You will be guaranteed a clone of the mother plants and they root so easily it’s how I make coleus every year. But if seed starting is your jam, go for it, you’ll end up with big beautiful plants and save yourself some money. A properly cared for seed started coleus can live quite a long time, so pick your variety and go from there.

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