Some holiday cards are bought. The best ones are painted. This season, grab a round brush and a bright palette and paint a little forest of rainbow watercolour Christmas trees: loose, joyful, and easy enough for a first-time painter. You'll practise colour blending and brush lettering along the way, too.

In this tutorial from Strathmore Artist Papers, artist Leslie Tieu (Leslie Writes It All) shows how to paint whimsical watercolour Christmas trees in a rainbow ombré, then finish them with hand-lettered calligraphy and a sprinkle of snow. Watch the video, then use our step-by-step notes and supply list to paint your own.

We've matched Leslie's supplies with what's on our shelves. Where we don't carry the exact product, we've picked an Opus favourite that does the same job.

• Paper: Strathmore 500 Series Ready Cut Watercolour Paper, Cold Press, 8" x 10": 100% cotton, acid-free, 140 lb (300 gsm). Cut to a standard frame size, so your finished piece is ready to hang.
• Paint: Opus Essential Watercolours Compact Tin Set of 12 (in place of the Daler-Rowney Aquafine 24 set from the video): vegan-friendly, vibrant colours that re-wet beautifully. It includes Opera Rose, Alizarin Crimson, Hansa Yellow Medium, Phthalo Green, Ultramarine Blue and Cobalt Turquoise for your rainbow. Titanium White is in there for snowy dots, and Payne's Grey for a moodier palette. It also comes with 12 empty pans so you can add your favourite colours.
• Brushes: Princeton Velvetouch Series 3950 Round, sizes 3 and 8: use the size 8 for the tree strokes and the size 3 for lettering and fine details.
• Sketching: Opus Essential Graphite Pencil Set of 6 and a General's Kneaded Eraser to sketch your lettering, then lift the graphite until it's barely there.
• Extras: paper towels, two jars of water, and a palette or plate for mixing.

Decide where your trees will go and leave a clear space for your message. Leslie saved the bottom corner for "Home for the Holidays." Lightly pencil your words in, then roll a kneaded eraser over them so only a faint guide is left. You'll still see it while you paint, but it disappears in the finished piece.

Load your size 8 round and start with a small cone shape for the top of each tree. Then build it down with short zigzag strokes that look like layered pine branches. Strokes in the centre fall straight down, and strokes on the edges flare out a little.

• Follow the rainbow: Work in ROYGBIV order, starting with reds and pinks, moving through oranges and yellows, then greens, blues and purples. Keeping that order makes the colour changes look smooth.
• Mind the negative space: The white paper between strokes is what separates one layer of branches from the next. Leave little gaps on purpose.
• Vary your forest: Change the height, width and starting point of each tree. Some can be tall and skinny, and others short with only three layers.
• Let it bleed: Where a wet layer touches the one below, let the colours mingle. Those soft blooms are part of what makes watercolour so lovely.

Bring a bit of the colour you just used into the next one. Mix a touch of yellow into your first green, a little of that green into the blue, and some blue into the purple. Each tree stays in the same colour family as its neighbours, so the whole painting hangs together. Want a cozier, moodier look? Add a touch of Payne's Grey to each colour.

Switch to your size 3 round. Brush calligraphy comes down to pressure:

1. Upstrokes: Use very light pressure and just the tip of the brush to make a thin line.
2. Downstrokes: Press down so more of the brush touches the paper and the line gets thicker.
3. Keep your brush fairly dry: Too much water makes letters blobby. Keep a paper towel close to blot excess.

Lettering is the trickiest part of this project. If small letters feel daunting, choose a shorter phrase or leave yourself more space.

Made a mistake? Blot the paint right away with a damp paper towel. Then lift what's left with clean water and a clean towel. Let the paper dry completely before you repaint, because wet paper will make new paint bleed.

Top each tree with a tiny star in a matching colour. Then dot or flick on some white to look like falling snow. Other ideas to try:

• Add tiny ornaments to each tree.
• Paint trunks in a matching colour, or in metallic gold for some holiday sparkle.
• Fill gaps with a few smaller trees.

Because the paper is a standard 8" x 10", your finished painting slips straight into a ready-made frame. That makes a sweet entryway piece or a hostess gift. Swap the message for a family name or "Welcome to the home of…" to make it personal.

Making a stack of holiday cards? Paint the same design at a smaller scale on Strathmore Watercolour Cards (5" x 6 7/8"). They're made from 140 lb cold press watercolour paper and come with deckle-edge envelopes.

Leslie points out that artist-quality paint and paper really do change the result. Cheaper paints can blend poorly and turn murky, and thin paper buckles under wet washes. Clear, bright colour on sturdy cotton paper is what makes these rainbow transitions glow. That's the idea behind Opus Essential: professional-quality colour at a price that lets you paint freely.

Painted your own rainbow forest? Tag us on Instagram. We'd love to see it.