Gravel Gardening: The Planting Formula to Success
Chester Road Planting

Gravel Gardening: The Planting Formula to Success

 

Chester Road Planting

In our first discussion of gravel gardens, we discussed a small planting around the Entrance Rock. This planting simply consists of tough plants in gravel, planted deep enough to reach the soil underneath. The inspiration came from the designer, Cassien Schmidt, a German garden designer who has developed naturalistic methods of planting in gravel. Schmidt came to the Scott Arboretum to hold a workshop and also consulted on the traffic circle planting on Chester road. Cassien has developed his way of planting as an easy and efficient formula mostly for municipal plantings and larger, low-maintenance plantings, but it can also be used for the home gardener.

planting

In the last few weeks we have installed a gravel garden around the bus stop in front of 101 Chester Ave., on Fieldhouse Lane, and replanted a gravel garden in front of the PNC bank (a replanting due to construction). photo credit: S. Quinn

After seeing so much success with the traffic circle in just under 2 years after initial planting, the College and Arboretum decided to plant more areas using gravel culture. In the last few weeks we have installed a gravel garden around the bus stop in front of 101 Chester Ave., on Fieldhouse Lane, and replanted a gravel garden in front of the PNC bank (a replanting due to construction). We used Cassien’s formula to create all of these gardens.

truck planting

Plants are planted within the grid. photo credit: S. Quinn

First we laid out a grid. Within the grid there is a list of plants and within that list there is a percentage of each type of plant. Different types of plants contribute different benefits to a group planting and act as a community.

Susan planting

Susan McGinley helping to plant the Chester 101 planting. photo credit: R. Rboert

In this planting there are 5% structural plants, 35% companion plants, 50% ground layer plants, and 10% filler plants. The plants chosen are mostly native and are selected for their ability to live through drought and full exposure to the sun. All of these are perennials but it is possible to incorporate woodies, as we did in the traffic circle.

Chester 101 planting

In this planting there are 5% structural plants, 35% companion plants, 50% ground layer plants, and 10% filler plants. photo credit: R. Robert

Within each group of plants there are between 4 and 6 different plants. For example: within the ground layer grouping there are four selections; Geranium cantabrigense ‘Karmina’, Ruellia humilis, Eragrostis spectabilis, and Asclepias tuberosa. In one block, if you need four ground layer plants, you can use one of each.

crated plants

The plants for each block were grouped in crates off-site, then moved to the site and placed in each block of the grid. photo credit: R. Robert

The plants for each block were grouped in crates off-site, then moved to the site and placed in each block of the grid. This made it easy for anyone to take plants out and plant randomly, and random is key. It’s hard sometimes to not think about where you’re placing plants, especially if you’re used to grouping or making swaths. In this planting design, the plants are all meant to grow together and through each other like they would in nature. It’s important to plant densely to cover the ground and inhibit weeds. Although the idea is to plant randomly, it is helpful along paths to plant things that won’t get big and flop over. If you have a narrow strip or an area that someone in a car needs to see over, it is best to leave the taller, structural plants out.

planting 2

It is important that the roots reach the soil level because they cannot grow out into the gravel. photo credit: S. Quinn

Planting in gravel culture is different. It is important that the roots reach the soil level because they cannot grow out into the gravel. The nutrients or water that most plants need are not present in gravel. In our gravel beds there is 6 inches of gravel above 4 inches of gravel-soil mix. To get to the soil, it takes a bit of digging and it’s important not to get soil in the gravel because that’s where the weed seeds can grow.

planted amsonia

After filling in with the gravel that has been dug out, it seems that you have just dug its grave because it is so deep, but this has been proven to work. photo credit: S. Quinn

I’ve found that a short-handled spade is best for digging. We dug deep, wide holes down to the soil, pulling the gravel layer out wide. It sounds harsh, but each plant gets the soil removed from its roots before it’s planted. Having a bucket close by for soil removal is important to keep soil from falling into the gravel. Removing the soil encourages the plant to go farther down with root growth and discourages weed seeds from growing out of the nursery mix that the plant was in.

gravel plant

Gravels covers the base of the plant. photo credit: S. Quinn

After filling in with the gravel that has been dug out, it seems that you have just dug its grave because it is so deep, but this has been proven to work. We have had some casualties, but the majority of plants have thrived in this situation.

soil removed

It sounds harsh, but each plant gets the soil removed from its roots before it’s planted. photo credit: R. Robert

Low maintenance is a major benefit of gravel culture. With the new plantings, we will water them as needed. The schedule is more frequently immediately after planting, and after a year, plants should be established enough not to need any watering except during an extreme drought. No fertilizers are added. Ideally, the planting should only need a few visits a year for possible weeding, and a cut back in the fall or winter to prevent debris from breaking down into soil for weed seeds to grow in.

Give gravel gardening a try in your sunny spot.

Susan Quinn
squinn1@swarthmore.edu
4 Comments
  • Jed Johnson
    Posted at 09:59h, 31 August Reply

    Great article – Thanks!
    What plants would be recommended for filler, companion, and structural to go along with the Geranium cantabrigense ‘Karmina’, Ruellia humilis, Eragrostis spectabilis, and Asclepias tuberosa.
    Thanks Again!

    • Becky Robert
      Posted at 15:02h, 25 September Reply

      Dear Jed,

      Below you will find a list of the other plants in this specific formula. These are all great plants but there are many more that can be used and it would be great to experiment with other perennials that you might think would work.

      Structural plants: Panicum virgatum ‘Hot Red’, Baptisia ‘Lemon Meringue’, Amsonia hubrictii, Schizacharium scoparium ‘Blue Heaven’

      Companion plants: Aster oblongifolia ‘October Skies’, Pycnanthemum flexuosum, Salvia nemorosa ‘Blauhugel’, Salvia nemorosa ‘Caradonna’, Liatris aspera

      Filler plants: Coreopsis verticillata ‘Zagreb’, Dalea purpurea, Geranium macrorrhizum ‘Lohfelden’ or ‘Ingwersen’s Variety’, Stachys officinalis ‘Hummelo’

      Susan Quinn

  • Jen Pfluger
    Posted at 14:03h, 31 August Reply

    Thank you for the continued commentary on this intriguing style of planting, including that the PNC Bank environs hasn’t been faring well due to construction and not the planting style itself. Is there any demonstarted success with gravel gardening in older planting strips between streets and sidewalks, i.e. part sun conditions with mature trees and roots to be careful around, or is the gravel approach only recommended for new/young beds?

    • Becky Robert
      Posted at 13:22h, 04 September Reply

      Dear Jeff,
      At this time, our oldest gravel planting is the Roundabout garden. We experimenting with this new technique and do not have experience with part sun with mature trees situations. Our exploration of this type of gardening is based off the recommendations and experiences in German gardens by Cassian Schmidt.

      Sincerely,
      Becky

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