Rockeries are often described as being easy maintenance, and a good option for people with little time to spare. The reality is very different and needs to be borne in mind whenever a rockery is being constructed.
Regular maintenance is essential to keep rockeries in good condition all year round. The limited planting space available has to be carefully monitored to ensure that plants are not exceeding their allotted area, or that weeds are taking over.
Weeding is a constant requirement. Grass and weeds can quickly overcome more delicate plants, but due to the confined locations hand weeding is frequently the only option. This may require scrambling around the rockery, or bending at awkward angles, which means ensuring rocks are not pushed out of place. Top dressings will need to be replenished every year to suppress weed growth and reduce evaporation from the soil. Avoid giving too much fertiliser as alpine plants are designed by nature to grow in fairly poor soil conditions.
Frequent deadheading will ensure longer period of flower production, as well as the removal of plant material that may cause growth problems. In the autumn, ensure that any leaves from nearby trees or bushes are not left on the rockery as this can damage rosettes and other alpine plants. Dwarf conifers and shrubs may need annual pruning to keep their shapes and restrict growth.
Vine weevils are common on rockeries. If plants do not seem to be thriving, check both the plants and the soil for any indication of vine weevil infestations. Adult vine weevils eat the leaves, while the grubs eat the roots. Sometimes rosettes and cushion plants can be pulled apart by birds searching for insects in the soil. Ants are another major problem, as they can dislodge plants and make it harder for roots to take up required nutrition when excavating their nests within the soil.
The overall structure of a rockery does need to be regularly checked to ensure that all the rocks remain safely and securely in place. Over time, rocks can be loosened by the effect of the weather, animals digging within the rockery, insects burrowing underneath or simply the weight of people climbing on the rocks. Simple precautions like installing bent hazel twigs or similar prunings around vulnerable rocks or to encourage people to use paths and steps can make an instant difference. Such twigs will also protect new planting while it is settling in and sending down roots.
Weather conditions can pose serious problems for rockeries. Steps and paths need to be checked regularly, especially during winter or periods of wet weather. Moss and algae growth can quickly create slippery, hazardous conditions. Long periods of dry weather can affect the stability of rocks placed into the ground, causing them to slip or fall out of place.
With climate change, floods and heavy rain are becoming an increasing problem for gardeners. If the garden is constructed on a flood plain or in an are known for flooding, then this should be borne in mind both in the construction and the maintenance of the rockery. After a storm, priority should be given to checking the stability of the rocks, and the condition of the plants as well as taking away excess water as quickly as possible.
Alpine plants can tolerate cold weather, but will struggle during wet conditions. Too much rain, or worse still flooding, can prove to be fatal to many alpines. Root rot can occur if the soil becomes too wet, and water does not drain away easily. If this becomes a regular problem, then adjustments may have to be made to some of the rocks, tilting them slightly downwards so as to increase the amount of water that can run off naturally.
Creating extra drainage channels is an alternative option, allowing the water to drain away safely from delicate plants. Decorative grit, pebbles and gravel will help with drainage as well as acting as a much needed mulch during hot weather. It will also deter slugs and snails, thus helping to maintain the overall appearance of the rockery.
Wind and rain can also remove soil from the rockery, washing it away from the plants. As a result, this can leave roots exposed. Pockets of soil may need to be replaced from time to time. Adding extra soil may be necessary together with some mulch. Choose mulches carefully to match in with the style of planting. Bark is ideal for large areas of planting, but if there are lots of rocks then grit or stone chips will suit the location better. Limestone chips should be avoided if any of the plants are lime haters such as azaleas.
Periods of droughts can also cause problems on rockeries. Alpine plants are not designed for hot conditions, so can easily dry out in hot weather. If the soil is dry to the depth of an inch, then watering becomes essential but take care to ensure that the dry soil does not fall away from the plants as this will cause further problems.