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The answer is: more than you think! In this article we’ll show you how to find out exactly how many plants you can grow neatly and efficiently in the space you have, whether that’s your yard, your neighbor’s yard, a highway median, or an empty city lot!
How much space do dahlias need?
Here’s the short answer: dahlias require 1 to 1.75 square feet per plant.
If you’re used to thinking in planting distances, that means planting each tuber 12 to 16 inches apart. A row 20' long x 4' wide (80 square feet) can grow up to 80 plants.
You may be thinking this is quite a bit closer than you’re used to planting dahlias in your garden.
So here’s the catch. The closer you plant each dahlia, the better quality your soil must be to maintain the same quality blooms; the more attention you will need to pay to watering in some climates; and the greater the risk of some annoying diseases like powdery mildew. The reverse is also true: the more space you give each plant, the less demanding it will be on the soil which feeds it, and the lower your likelihood of disease.
However, it’s also important not to space your plants too far apart, especially if you are planning to hand weed, since every inch of exposed soil not shaded by a desirable plant is habitat for weed growth.
At Sunset View Farm, because we grow for production, we plant our dahlias closer together in the field than most gardeners do at home; but most gardeners plant dahlias quite a bit farther apart than is necessary for their maximum flourishing.
We encourage you to not be afraid to let your dahlias get cozy with each other if space is tight for you, so long as the close accommodations come with a gardener’s tender care!
How to calculate how many dahlias you can grow in your space
Let's return to our example.
First, measure out the rows in your space. Four feet is a common row width, but some gardeners prefer three foot rows for easier harvesting. For our example, we’ll use the more common four foot width row.
So, measure out the length of each row in your space, and multiply the length by four feet. Let’s say you have a 20 foot long stretch of yard. Here’s what that calculation looks like:
20’ long x 4’ wide = 80 square feet of growing space in that row.
We know that dahlias require 1 square foot minimum growing space, so from here the calculation is easy. We divide the square footage of the row by 1!
80 square feet per row / 1 square foot per dahlia = 80 dahlia plants per row.
It’s important not to forget pathways when calculating your total available growing space, as they can take a significant chunk of your total square footage.
The catch: not all “space” is suitable
We would all agree that a 100 square foot space on a concrete floor in a dark warehouse is not the same as 100 square feet in the average suburban lawn.
In the same way, not every suburban lawn is suitable for growing dahlias either. Dahlias require a lot of sunlight; relatively loose and well-draining soil; and a good balance of ventilation along with protection from major wind.
Here a few conditions which automatically disqualify a piece of land from consideration for growing dahlias, unless steps are taken to change the conditions:
· Deep or even moderate shade. Overhanging trees that keep your dahlias from getting at least 8 hours of full sun all summer long will stunt the plants’ growth, sometimes to the point of not flowering at all.
· Poorly draining or flooding soil. Dahlias cannot survive on a patch of land where water frequently stands or pools
· Extremely hard or depleted soil, or soil with the wrong pH. Dahlias require a lot of nutrients, along with room for their shallow but wide roots to grow. Though sometimes the least obvious problem, soil conditions are often the easiest to fix.
These issues are not always insurmountable, however. Trees can be pruned, drainage ditches dug, and soil can always be amended.