In the world of rock gardening, containers play an important role in growing petite perennial plants. Plants such as dwarf or miniature conifers can be grown as specimens in pots. Other petite plants including small conifers can be combined to duplicate, on a miniature scale, a natural grouping of plants. Some plants have proven to be “intractable” (ungrowable) planted into the ground and yet thrive when grown in containers. Cold hardy cacti and succulents are also wonderful potted specimens. Many accomplished rock gardeners grow their plants in both rock gardens and containers to make their plantings more diverse and interesting.
Types of Containers and Pots
Petite rock garden plants can be planted into many types of containers. But being perennial, the plants must be grown in containers that are weather proof (not cracking from freezing and thawing soil) over the winter months. This is unlike pots of annuals that are emptied after frost kills the plants. Traditionally, the English and Europeans (who started the art of rock gardening) used farm troughs carved from stone to containerize their rock garden plants. But stone troughs soon became scarce and expensive. A new type of trough construction was devised using a material known as hypertufa. This combination of Portland cement, sand and peat moss proved to be very durable and could be molded into a variety of different shapes .
Traditional hard-fired pots such as terra cotta and glazed pots can also be used. But it is recommended that you actually plant in plastic pots and drop them into it into a slightly larger hard-fired using small bark chips to fill the sides and bottom between the two pots. This protects the hard-fired pot from cracking by separating the soil mix from the sides of the ceramic pot. Inside the plastic pot, the soil can freeze and thaw and not crack the plastic.
Designing your rock garden containers
Hypertufa troughs are especially suited to creating miniature petite plant vignettes. Designed to be wider and longer than they are deep, they are roomy and provide space for multiple plants, ornamental rocks and small pieces of weathered wood to be used together. Some large hypertufa troughs are very heavy when filled with soil and plants and are not intended to be move once planted. Individual specimen plants such as dwarf conifers, cacti and succulents can be planted into traditional pots then grouped with hypertufa troughs . This is a very effective way to display a diverse collection of potted rock garden plants. Instructions to make your own hypertufa can be found here.
Soil mixes for rock garden containers
The right soil mix is essential for a rock gardener to have long term success with their containers. As you would expect when you ask three chefs for a recipe for chili, you’d get three slightly variations in their ingredient list. The same goes for nursery soil mixes. Kelly Grummons, owner of Timberline Gardens, long time rock gardener and container grower recommends the following soil mixes.
For long term growing in pots like conifers and woody plants
For cacti and succulents (for both indoor and outdoor use)
If scoria is not available, use expanded shale pellets in place of the scoria. Both scoria and expanded shale have a lot of pore space within them to absorb and hold water while also providing improved drainage. The fine hair roots grow around and into these porous materials where they can extract water when the soil is dry.
Ralph Peter’s Potting Mix for cacti and succulents (best for outdoor use)
Fertilizing for long term success
Planted pots and hypertufa containers need regular fertilization to keep the plants healthy. Of course we want to keep the plants small, so a dilute amount is best. Fertilize monthly during the growing season. Seaweed and fish emulsion mixes are excellent. Cut the recommended rate of the emulsion in half.
For cacti and succulents, it is important to regularly use an acidified fertilizer mix for both the above cacti and succulents potting mixes. Even though many of these plants love alkaline limestone soils, the root environment in a pot or hypertufa trough is different. This formula comes from Steve Brack, owner of Mesa Gardens and a world renowned expert on cacti.
Thanks to David Salman for providing this information.
READ this blog on hypertufa trough construction from the Chicago Botanic Gardens.
Plant Select® Petites debuts well-adapted, smaller plants that have not yet been readily available to gardeners. Enjoy these treasures in garden situations where small gem-like but tough plants are best suited: troughs, permanent containers, rock gardens, patio gardens, fairy gardens, green roofs, and smaller gardens.