What kind of liner do you recommend for a metal planter box to protect it from soil acidity?

Ah, the noble metal planter box! You stand so strong and stylish in the garden, but I hear your silent plea. That rich, life-giving soil inside you can sometimes turn a bit sour, its acidity slowly whispering threats of corrosion against your metallic walls. Fear not, for I am here to recommend the perfect armor—a trusty liner.

First, let's talk about the heavyweight champion: the EPDM Pond Liner. This is my top recommendation for serious, long-term protection. Think of it as a flexible, rubbery shield. It's incredibly durable, resistant to UV rays and extreme temperatures, and most importantly, it forms a nearly impermeable barrier between your soil and the metal. It laughs in the face of acidity. For a slightly more budget-friendly but still robust option, consider a heavy-duty plastic sheeting or a HDPE liner. They're excellent moisture barriers, though ensure they're thick enough to resist punctures from eager roots or sharp stones.

Now, for a more breathable approach, meet the Landscape Fabric. This geotextile won't hold water, but it's a fantastic first layer. It allows for drainage while creating a physical buffer that minimizes direct contact between the damp, acidic soil and the metal. I often suggest using it in tandem with a plastic liner—fabric against the metal for cushioning, then plastic for the ultimate seal.

My dear gardening friend, the key is creating a complete separation. Whichever liner you choose—be it the mighty pond liner, the reliable plastic, or the breathable fabric—ensure it covers every interior inch, from the bottom up the sides. Trim it neatly, secure it, and perhaps add a layer of drainage pebbles at the very bottom. This simple act of care will let your metal planter box stand proud and pristine for seasons to come, focusing solely on its true purpose: nurturing vibrant life.