To include soil requirements (free draining, good aeration, ability to hold moisture, appropriate pH, low nutrient content, free of weeds, pests and diseases) and preparation for planting in rock gardens, scree beds and gravel borders.


ROCK GARDEN PLANT A true alpine plant or not, displaying an abundance of attractive, brightly coloured flowers, and their diminutive form and compact habit make them particularly suitable for growing in a relatively small space.

PLANTING A ROCK GARDEN Growing mediums for alpines and rock garden plants: The majority of alpines and rock garden plants have evolved to grow in a soil made up of gravel and rock fragments with a small amount of humus-rich detritus to retain moisture. To successfully grow these plants, it is therefore important to reproduce this freely-draining growing medium as closely as possible. Whilst ordinary garden soil may be modified by adding peat substitute and/or grit, moisture-sensitive species will require a faster draining medium, such as the scree mixture, which contains a higher proportion of grit; Planting areas should be dug out and filled with 10 cm (4 in) of small rubble, crocks or stones, and an appropriate soil medium; Standard Mix: This medium is suitable for most rock garden plants; the grit or sand ensure good drainage, whilst the humus-rich materials provides moisture retention; 1 part sterilized garden soil; 1 part coarse grit or sharp sand; 1 part peat substitute (or peat). Acid-Loving Plants: 4 parts lime-free leaf mould, peat substitute (or peat) or composted bark; 1 part coarse sand. Special Mix: Some specialist alpines from high altitudes, e.g., Androsace species, require an extremely free-draining compost. Use the following mixture: 2 or 3 parts chippings or gravel; 1 part loam or leaf mould (or peat substitute or peat).

Scree Mixture: 1 part sterilized garden soil; 1 part peat substitute (or peat); 3 parts coarse grit or stone chippings (not sand); This mixture for moisture-sensitive species may be amended to suit your requirements; increase the proportion of stony material to make a compost which drains more freely, or reduce it in dry areas. Alternatively, those gardens in dry regions may use a more retentive mix: 2 parts loam; 2 parts leaf mould; 1 part sharp sand; 4 parts stone chippings.

Planting: Before you start to plant, water all the plants thoroughly and allow them to drain; Slide each plant carefully out of its pot and tease some of the roots out to encourage them to spread; Remove any moss and weeds from the compost and check the roots and top-growth for pests and diseases; Using a trowel or hand fork, make a planting hole large enough to accommodate the root ball; Ease the plant into the hole so that it sits with the collar slightly above the surface of the compost, then fill in with compost; Firm around the plant gently, making sure that there are no air pockets between the root ball and the compost, and then label; Add a top-dressing of grit or gravel; If plants are to be planted into a crevice, dig out a hole slightly larger than the root ball, and push the roots to the back of the crevice; Fill in with soil, tamping it in with a narrow implement. If the crevice is bigger than the plant, you may find that you need to add in some pieces of stone to wedge the plant in; Whilst alpines and rock garden plants may be planted at any time of the year, it is usually best to do so in spring to early summer; At this time, the plants are growing actively and will establish quickly, and you will avoid planting in very wet, dry, freezing or hot conditions; When all the plants are in place, check that the whole area is properly top-dressed and then water them in thoroughly. Keep the plants moist until they are well established and are starting to make new growth, this may require weekly watering until the roots have penetrated the surrounding compost; Crevice plants may be kept moist by using a water spray; Once the plants are established, there should be no need to water them except during a drought; You may need to re-firm any plants that may have worked loose from time-to time, adding new compost if necessary.


Identify poor drainage: Surface symptoms – indicator plants (rushes, reeds, moss, buttercups, docks). Laying water. Yellow patches in crops/lawns; Pit test – high water table, soil smell (sour/metallic), soil colour (grey mottling/or rust patches); Obvious surface run off – paths/patio/bases of banks.




Identify poor drainage: Surface symptoms – indicator plants (rushes, reeds, moss, buttercups, docks). Laying water. Yellow patches in crops/lawns; Pit test – high water table, soil smell (sour/metallic), soil colour (grey mottling/or rust patches); Obvious surface run off – paths/patio/bases of banks.

SOIL PH The range of garden soils is given by the RHS as 4-8 though some books go to 8.5.

State why 6.5 is the most suitable pH for a wide range of plants in the British Isles.

Normally: Plant growth of a great range of plants is good in the range of 6→7.5; A good pH for most gardens is 6.5 as it suits “most plants” and most plant nutrients are readily available (this alters slightly according to the soil’s texture).

Soil Structure (soil organisms, crumb formation): Worms dislike acid soils and so such soils have few worms. Worms secret alginate into the soil that acts as a soil glue creating good soil structure. Calcium products can be used to help break down clay soils chemically, so improving the structure (calcium carbonate and hydroxide will alter the soil pH, calcium sulphate will not). Soils with natural high free lime content (calcareous clay) will not respond to the application of lime products.

Nutrient Availability: See above. Nutrient availability is affected by both soil pH and soil texture.

Lime Induced Chlorosis: Where the free lime in the soil locks up iron and magnesium molecules in the soil and makes them unavailable to the plants. This causes a mineral deficiency with iron showing up as yellow young leaves and magnesium as yellow inter-venial patches on old leaves (treat plants with sequestrene of iron).







Routine maintenance to include trimming, mulching with grit, winter protection, weeding, control of ONE relevant pest and ONE disease for these situations.

MAINTAINING A ROCK GARDEN Once established, rock gardens usually need to be regularly weeded, fed at intervals and watered whenever the soil becomes dry. Plants should be kept tidy and cleared of any dead flowers or leaves, and checked regularly for signs of pest infestation and disease. Top-dressings should be replenished every year to reduce evaporation of water from the soil and to suppress weed growth. In cold or wet winters, some plants may need some additional protection.

Watering: Once established, most alpines and rock garden plants will not need any additional watering unless the weather is very dry. Check the soil – if it is dry at a depth of 3-5 cm (1¼-2in), water thoroughly until the soil is moist. Soak the area occasionally in early mornings or late evenings, rather than applying frequent small amounts of water. Never water in frosty weather; The soil in troughs will tend to dry out more quickly than in rock gardens; hand water each plant individually so that it receives the right amount of water. Feeding: If you used a good compost with slow-release fertilizer when planting, you should not need to feed the area for several years. However, once growth slows down and flowers become more sparse, scratch in a mixture of slow-release fertilizer and bone meal around the plants each spring; You will need to replace pockets of soil every few years if vigorous plants are grown in them, or when replanting. Weeding: To minimise weeds during the first few years, always use sterilised compost when planting. Remove any weeds that do appear immediately so that they do not have chance to flower or set seed. Most weeds may be removed using a three-pronged cultivator which will also loosen and aerate the soil. You may need to use a translocated weedkiller to eradicate established perennial weeds. Top-Dressing: The top-dressing applied to alpines and rock garden plants depends on the species of plant grown, but in general, it should complement the stones used within the planting areas. Stone chippings or coarse grit are suitable for most situations, however, never use limestone chippings around lime-hating plants; Renew the top-dressing when necessary, topping up whenever bare patches appear. Make a thorough check in late autumn to ensure good soil coverage for the winter, then re-check in spring. Winter Protection: Alpine plants may need additional protection in the winter – not necessarily from the cold, but from the damp. This is especially true of cushion plants, and those with hairy leaves. Cover troughs with a pane of glass or Perspex, propped with bricks to ensure that the air circulation around the plants is not restricted. Weigh this down with another brick or stone.



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