Planting a new border is tremendous fun, and it is exciting to see the new plantings develop. To get the best result, and avoid constant problems with weeds and soil nutrients later, make sure that you get the preparation right before you plant.
Most perennial and mixed borders require similar preparation before you plant. This preparation will break up the soil, clean it of unwanted weeds and enrich the soil to promote great plant growth. You cannot really treat a whole border once it has been planted, as very often the permanent, woody plants cannot be removed later. This is your best opportunity to add compost and organic matter that will feed your plants and make them strong and healthy. Make the most of the opportunity before you start planting.
Add plenty of bulky organic matter (humus or compost) to improve the soil structure and to add nutrients. Plants need to be able to push their roots through the soil and to gain the food they need. You cannot totally change your soil, but it does not hurt to know what you are working with.
Work the soil over thoroughly, removing all weeds so that your plants will get a good start in a friable soil without competition for invasive interlopers! Many experts recommend double- digging a new border, that is, digging to 45-60cm. Depending on your soil structure this may simply mean that you are digging into gravel (on the Canterbury Plains), or bedrock! Take care that you do not mix the subsoil (usually a lighter colour) with the topsoil, but add plenty of organic matter to both.
After digging, leave the soil to settle. Ideally, you should dig over a new border in autumn and leave for the winter. But gardeners do not always have control over time-scales, are busy and frequently impatient to get going with planting! Do try to let the earthworms do their stuff though, and leave the newly dug border for a few weeks. You can remove annual and perennial weeds that emerge over the coming weeks, further cleaning the border.
If your soil is waterlogged or damp then you can improve the drainage by removing the topsoil, digging into the sub-sol and adding stones and gravel. Be careful though that you don't create a puddle in this hole, in truly wet ground you must lay an effective field drain to remove excess water.
If you have a desperately heavy, clay soil or a disastrously sandy light one, then one solution is to create a raised bed using imported soil to fill it and lifting your plants out of their clay puddle or sandy home. Raised beds are also great on steep slopes (where they become a series of terraces), slowing run-off and conserving moisture.
Soil Types You can buy a soil test kit at most plant nurseries and this will tell you if you soil is acid or not.
Soil structure also plays a part in determining what will thrive in your border. Three main types of soil - clay, loam and sandy soil.
You can determine what you have quite simply. Take a handful of soil and rub a small amount between your fingers. If it crumbles and falls out of your hand you have a light sandy soil. If a small ball forms them you have a loam. If the ball is tight and sticky then you have a clay soil. There are, of course, many gradations of soil between these three categories.
Loams are good garden soils with plenty of humus or organic matter, are well drained yet moisture retentive, and are friable allowing plant roots to penetrate easily. These soils support the dense planting in a border, where each plant requires and competes for nutrients.
Light, sandy soils are often dry as water drains away too quickly, leaving an environment that will sustain only drought-loving plants. Nutrients are frequently washed out of light soils, leaving them poor and unable to support many garden plants. These soils will need the addition of lots of compost to add nutrients and build soil structure.
Clay soils are rich in nutrients but also present a problem. They are cold and sodden in winter, baked hard in summer. There are plants that love clay, but you will increase the range of plants you can grow if you add grit and lots of compost to improve soil structure and drainage.
