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How to Grow Perennials

How to plant and grow perennial plants

Planting perennials

It's best to plant out or pot up your perennial plants as soon as possible. If you need to delay planting then keep your plants in a bright, cool but frost-free position. Ensure the roots are kept moist. Bare-root perennials can be planted straight in the ground whereas plug plants are best potted up and grown on before planting out into their final positions.

Perennials will stay in your garden for a long time so it's important to prepare the site you are going to plant them in. Break up the soil with a garden fork - aim to dig to at least the depth of the blade on your fork or spade. Incorporate plenty of organic matter such as compost or well-rotted manure to improve the soil structure and provide nutrients for your plants. Many perennials are also suitable for growing in containers.

Perennial plug plants

Many of our perennials are supplied as plug plants and are best potted up and grown on before planting outside. Pot them up into large module trays or small individual pots and place in a greenhouse, cold frame or sheltered spot next to a house wall outside, to offer the young plants some protection. Make sure the compost doesn't dry out, but ensure that water can still drain away so the roots don't become waterlogged. For more information on how to grow plug plants click here.

Container-grown perennials

If your young perennial is container-grown, water the plant thoroughly before planting out. Dig a planting hole one and half times the size the root ball. Gently slide the plant out of its container and carefully tease out the roots around the side and bottom of the root ball with your fingers. Place the plant in the prepared hole and check that the crown of the plant sits at the same level in the ground as it was in the pot. Fill in around the root ball with soil and firm the plant in. Plants should be watered thoroughly after planting.

Bare-root perennials

Bare-root perennials should be planted on delivery to prevent dehydration of the roots. The plastic packaging will keep bare-root plants alive for a short period but if planting is heavily delayed it may be best to 'heel-in' your plants. This simply means to dig a temporary trench in ordinary garden soil and place the roots inside. Cover the roots with soil, firm in and water well. This will keep your plants alive until you are ready to plant them in their final position. If the ground is frozen or waterlogged then pot up your bare-root perennial, water sparingly and place in a cool position for planting out at a later date. When you are ready, dig a hole wide enough to accommodate the bare-root with its roots spread out and deep enough that the crown of the plant is just a few cm below soil level. Backfill the hole with soil and firm the plant in gently. Leave a slight depression around the plant - this will help to direct water towards the roots. Water well to settle the soil.

How to plant a rhizome

Rhizomes are swollen underground stems found on plants such as bearded iris. Plant the rhizomes at the soil surface so the top of the rhizome is exposed to the air. Planting too deeply may cause the rhizome to rot.

Aftercare of perennial plants

Perennials plants are relatively low maintenance. Mulch them annually in the spring or autumn by spreading a 5-10cm layer of compost, well-rotted manure or recycled green waste around the crowns of the plants (take care not to bury the crowns themselves). This will help to suppress weeds, retain moisture and improve the soil structure. For the best flowers it is worth applying a balanced slow-release fertiliser to the soil in the spring. Keep on top of the weeding around your perennial plants - if you allow weeds to grow and seed they will start popping up through the crown of your plant and can be tricky to eradicate. Dead-heading (removing spent blooms) may encourage further flowers although some perennials such as oriental poppies, Chinese lanterns, and echinacea have very attractive seed heads which you may like to leave on the plant.

In the autumn when your perennials have finished flowering and the foliage has died back, cut any dead foliage to the base and remove it. Some perennials, such as oriental poppies, have attractive seed heads, whilst grasses have attractive foliage so you may wish to leave these intact for winter interest. Some woody perennials such as penstemons should not be cut back in the autumn but should be clipped close to the base in the spring.

Most perennials should be lifted and divided every 3 years to maintain vigorous growth. You should also divide perennials if clumps have become congested or flowering is less profuse. Division should be carried out in the autumn or spring before plants start into active growth. This also provides a good opportunity to work in some well-rotted manure or compost to maintain soil fertility. Simply loosen the soil around your perennial and lever it out of the ground with a garden fork. Take off any dead leaves and stems. Aim to break the clump into sections by inserting two garden forks back-to-back in the centre of the clump and moving the forks backwards and forwards to tease the clump apart. Further divide the sections into as many pieces as you require although make sure you leave at least two growth buds per piece. The bigger the divisions, the quicker they will establish and flower. For tough or fleshy roots you can divide your perennials with a spade; slicing through the crown to leave pieces with at least two growth buds. Replant the divisions straight away at the same depth as the original plant. Ensure the roots are well spread out in their planting hole and the plants firmed in. Water thoroughly afterwards.

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Perennials will stay in your garden for a long time so it is important to prepare the site properly before planting.