Trough planters are the unsung heroes of commercial landscaping. Sleek, linear, and incredibly versatile, they can define spaces, manage foot traffic, and bring a vibrant touch of nature to urban environments. But a common pitfall in commercial projects is selecting planters based on aesthetics alone, only to find the plants inside are struggling or the scale feels “off.”

Choosing the correct size isn’t just about looks; it’s about plant health, project budget, and long-term maintenance. This guide will walk you through the key considerations to ensure you select the perfect sized trough planter for your commercial property.

Why Size is More Than Just an Aesthetic Choice

Before we dive into dimensions, let’s establish why size matters so much:

Plant Health:

This is paramount. The volume of soil in a planter acts as the plant’s root system’s home. Too small, and roots become “pot-bound,” leading to stunted growth, water stress, and nutrient deficiency.

Structural Impact & Scale:

A planter that’s too small will look lost in a large plaza, while one that’s too large can overwhelm a narrow sidewalk and impede pedestrian flow.

Watering Frequency:

Smaller planters hold less soil and therefore less moisture, meaning they’ll dry out much faster. This can significantly increase irrigation demands and maintenance costs.

Budget & Installation:

Larger planters are more expensive, heavier, and can be more complex to install, especially if they need to be craned into place.

The 3 Key Dimensions to Evaluate

When looking at trough planters, break down your decision into these three aspects:

1. Length: Defining the Space

The length of your trough planter is its most defining visual characteristic. It’s what creates that clean, architectural line.

Short Lengths (under 1.2 meters): Ideal for framing entryways, creating subtle divisions between seating areas, or adding accents to balconies and patios. They are highly versatile and easier to handle.

Medium Lengths (1.2 – 2 meters): Perfect for lining walkways, defining the edge of a building façade, or separating a restaurant patio from the public sidewalk. This is a very common and functional size range.

Long Lengths (2.4+ meters): Make a bold architectural statement. Use these to create strong visual barriers in large plazas, median planters on boulevards, or as a centrepiece in a public square. Remember to factor in how you will transport and install a planter of this scale.

Pro Tip: For very long runs, consider using multiple shorter planters placed end-to-end. This creates a continuous look while offering flexibility for future reconfigurations and easier replacement.

2. Width: Balancing Form, Function, and Horticulture

The width determines the planter’s footprint, but it’s also critically linked to plant health and sourcing.

Narrow Widths (under 400 mm): While available, these are generally not optimal for plant health as they restrict root growth and soil volume. They are typically used only when space is extremely limited, such as on a narrow balcony, to maximize path width, or for a specific climber fixed to a wall. Be prepared for more frequent watering and potential constraints on plant choices.

Standard/Medium Widths (400 – 450 mm): This is the most popular and recommended width range for a key horticultural reason: it aligns with the standard 400 mm nursery pot that many shrubs and perennials are grown in. This size provides a seamless transition for the plant, offering ample soil volume for healthy root development, moisture retention, and nutrients. It’s the ideal balance between space efficiency and plant vitality.

Wide/Bench Widths (450 – 600 mm): These planters offer more space for elaborate plantings or deeper-rooted species. Widths up to 600 mm are still practical for pre-fabricated trough planters. They can double as informal seating in public spaces.

Beyond 600 mm: While cube or round planters are feasibly manufactured up to 1100 mm wide, trough planters beyond 600 mm in width are generally better suited to being built on-site using rendered brick or concrete. This is due to the significant structural, weight, and transportation challenges of a single, pre-cast unit of that scale. For very wide linear planters, a custom built-in solution is often more practical and cost-effective.

3. Depth: The Foundation for Healthy Roots

Depth is arguably the most critical dimension for the long-term health of your plants. It’s the factor that is most often underestimated.

Shallow Depth (under 450 mm): Suitable for seasonal colour (pansies, petunias), succulents, herbs, and ornamental grasses. Not recommended for any permanent, woody plant material as it won’t survive a freeze or drought.

Standard Depth (450 – 600 mm): A good minimum for most commercial applications. This can support large shrubs, bamboo, and some smaller, shallow-rooted trees. It provides a more stable environment for perennial plants.

Deep/Arboreal Depth (600+ mm): Essential for trees. If your design includes any type of tree, this is non-negotiable. A deep soil profile allows for proper root establishment, anchoring the tree against wind and providing the moisture and nutrients it needs to thrive for years. Always check the mature root ball size for your specific tree species. In most cases large cubes and round planters are more suitable for large trees like this.

A Practical Sizing Checklist for Your Project

Ask yourself these questions before making a final decision:

1. What is the primary purpose? (e.g., visual screen, pedestrian guide, tree installation, seating?)
2. What plants will go inside? Research their mature size and root depth. Always choose the planter for the mature plant, not the starter plant.
3. What is the scale of the surrounding architecture? A tall building can handle larger, more substantial planters.
4. What are the traffic flow patterns? Ensure the planter placement and width don’t create bottlenecks or hazards.
5. What is the maintenance plan? Deeper planters will require less frequent watering. Do you have a reliable irrigation system?
6. What is the budget? Account for the cost of the planter itself, the soil to fill it, and the plants.

Quick-Reference Size Guide

Use Case	Recommended Minimum Size	Ideal Plants
Seasonal Annuals/Color	305 mm D x 305 mm W	Petunias, Marigolds, Lettuce
Ornamental Grasses	405 mm D x 405 mm W	Fountain Grass, Blue Fescue
Large Shrubs & Bamboo	510 mm D x 610 mm W	Boxwood, Hydrangeas, Clumping Bamboo
Small Ornamental Trees	610 mm D x 760 mm W	Japanese Maple, Crape Myrtle, Olive
Seating Wall & Tree Combo	610 mm D x 915 mm W	Any of the above, with a sturdy tree

Final Thoughts

Selecting the right sized trough planter is a strategic decision that blends art and science. By carefully considering length, width, and depth in the context of your specific project goals, you can create a beautiful, functional, and sustainable landscape that enhances your property for years to come.

When in doubt, consult with a professional landscape architect or a reputable commercial planter supplier. Their expertise can help you navigate these choices and invest in a solution that delivers on both form and function.