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Select your rocks to create the trough garden. Think about textures and the colors of your rock as you work. Pick out plants that will do well in the location that you have chosen to put your trough. Consider the “thriller, filler, and spiller” philosophy. Think about picking out plants that can survive the winter. Give your plants some space. Add a decorative mulch (optional). Maintain your rock garden.
The rocks you choose should be based on your personal preferences. The combination of one larger and one smaller rock works well, or consider using long, thin rocks placed in rows for another nice effect. Consider using rocks of the same color and variety rather than a mixture; this can look more natural and harmonious. All the rocks should be buried so that half of the rock is covered with soil. Doing this will keep the rocks in place. You may wish to plant towards a single raised point, such as a tall rock or piece of driftwood arranged semi-vertically. A slightly triangular effect also works well. Most rock garden plants (such as Alpines) favor sun. If you plan to place your trough in a shady site then you may need to choose shade-tolerant plants. Plants like alpines and sedums, or Aubretia, work well in sun; consider planting ferns, begonias and small hostas in shade. Some gardeners swear by the rule ‘a thriller, a filler and a spiller’ for container planting. One showy plant to catch the eye and thrill it, a plant to fill out space and provide an attractive backdrop, and a trailing plant to spill over the edge and create an interesting organic shape. Remember to plant trailing plants near the edge of your trough so they cascade over the side. Remember that if you choose only plants that disappear over the winter, your rock garden will look very sad for several months of the year. Consider planting some evergreens such as the sedum Stonecrop or the alpine groundcover Matted Globularia (Globularia repens). Rock gardens aren’t usually covered in plants that are crowded together. Leave your plants some breathing room and allow the rocks to be visible. They will need room to expand over time, especially if they are ground cover plants or creeping varieties. Once you finish planting your trough, consider adding an attractive inorganic mulch using something like pea shingle or shale. This sort of mulch will hide any bare soil between the rocks and plants and it will also stop the plant foliage from coming into contact with wet earth, which can cause the leaves to rot. Some alpines are adapted to absorb heat from the rocks they grow on. Mulch also suppresses weeds; weeds can be a problem in a rock garden because of the gaps between plants. Rock gardens aren’t intended to be high maintenance. You may need to attend to weeding. It’s important that your plants don’t drown in their planter. If drainage is a problem in the trough, consider sheltering it during the wetter winter months.  Consider feeding the plants in the springtime. Many of the alpines and sedums used in rock displays are very drought tolerant. However, you should consider watering during dry spells, depending on which plants you chose. If you are planting in shade, consider protecting plants such as hostas from slug and snail attack.