Updated: Feb 26, 2018
By Amber Lehrman
Planting perennials around the borders of raised vegetable beds is an ideal way to increase crop yields without costing a lot of money or expending much effort.
Yet, many gardeners are still using wooden boards or clay bricks to create borders in their raised beds, resulting in few if any benefits other than containing the soil and over time, decomposing into mulch.
But using perennial plants in the borders of raised vegetable beds not only helps hold the soil in place, these plants can also provide a complete habitat for beneficial insects and pollinators, as well as produce additional crops that can be harvested and eaten.
Sound good? Here are a few tips to get you started:
Select Companion Plants
A good perennial border will have three characteristics:
1. Short, so it won’t shade out the vegetables. Less than 12” is ideal.
2. Shallow rooted so that the roots won’t take over the vegetable bed.
3. Slow growing so that it requires minimal pruning to keep it on the bed sides.
Examples of perennials that work well in the borders of raised vegetable beds include thyme, lavender, oregano and alpine strawberry.
Start by deciding what varieties of plants you want to grow. Selecting several different types of perennials to lengthen the bloom time throughout the summer (which attracts predatory insects and bees to the garden) is a great way to control pests and pollinate the rest of your garden.
Give Them Room To Grow
Most thyme varieties recommend planting 18” to 24” apart. For perennials like this, the spacing is usually based on the plant’s filling that space in the third year of growth. If you want them to fill in the sides of the bed sooner than that, you will need to plant them closer together.
You can generally cut the spacing by up to half (so thyme spaced 12” apart instead of 24”). Based on what you decide and the total perimeter of raised bed, you can figure out how many plants you need. For example, if you have a 4’x12’ raised bed, the total perimeter is 32’. If you are spacing the plants 2’ apart, then you will need 16 plants.
Water, Mulch and Prune
Slope the sides of the bed at no more than a 45 degree angle and plant your perennials about a third of the way up the side of the bed. Be sure to mulch the plants and the sides of the bed with a long lasting mulch – straw, wood chips or similar – to prevent erosion and retain moisture as the plants establish. Most perennials should be planted in the spring, but look at the recommendations for your selection to be sure.
For the first year, you will just be watering the border along with your garden veggies and keeping the mulch in place as the plants fill in. Its easy to get discouraged at this point because most perennials will grow very slowly above the ground for the first year. They put all their energy into the roots and then take off in years 2 and 3. Just give them time.
Once the plants fill in, maintenance will involve an annual cutting in the spring or in the spring and fall (depending on your soil and climate) to keep it out of the planting bed.
For thyme, the cuttings can go straight to the kitchen for use. It is a good idea when you trim the top growth each year to also take a shovel and just push it vertically through the bed along the top of the side slope to trim the roots at the same time. That will ensure that over time your border doesn’t take too much away from the main vegetable crop.