Plant by 31 March: drought-tolerant perennials for a water-saving border

Planting now saves effort and water while creating resilient borders.

This only works if you make the calendar work for you. Planting new perennials by the end of March gives them cool soil, time to establish roots and less stress. The aim is a sunny border sustained by rainfall, without daily watering rounds.

31 March: the deadline for drought-tolerant perennials

By late March, winter dormancy is ending, sap is rising and the soil still retains moisture. This window gives roots a head start before hot weather arrives. According to the French environmental agency Ademe, early planting measurably reduces water requirements. Waiting until May exposes young plants to heat, increasing transplant stress and the amount of watering needed.

“Anyone who plants by 31 March takes advantage of cool soil and saves dozens of watering sessions in summer – through biology, not merely appearance.”

Experience bears this out. A Gaura planted in May often needs watering every 48 hours during heatwaves. Over a season, that can readily amount to 200 litres more than a plant put in during March. That is equivalent to two full watering cans each week, for weeks on end.

Five perennials that tolerate heat and drought

These plants remain dependable even through a bone-dry July. They thrive in sunshine and wind, provided the growing medium drains well.

Plant	Strength	Height	Position and soil
Perovskia (Russian sage)	Grey foliage limits evaporation; flowers blue for a long period	80–120 cm	Full sun; poor, free-draining, lime-tolerant soil
Sedum ‘Autumn Joy’	Succulent leaves store water; late flowers feed bees	40–60 cm	Full sun; sandy to stony, low-nutrient soil
Gaura lindheimeri	Taproot reaches deep reserves; moves gracefully all summer	60–100 cm	Full sun; light, well-drained soil that is not too rich
Echinops ritro (globe thistle)	Extremely tough once established; steel-blue spheres	60–90 cm	Full sun; dry, lime-loving conditions
Lavandula angustifolia (English lavender)	Fragrant and attractive to insects; does not need much water if it drains away	40–70 cm	Full sun; stony, poor soil; avoid waterlogging

Tough cranesbill varieties (Geranium) make suitable companions. They rarely die back severely, cover the ground and cope with anything from partial shade to full sun. In late winter, pull away the dry remnants by hand; they almost come away by themselves.

How to plant correctly in March

Prepare the root ball

• Submerge the potted root ball in water until no more bubbles rise, which takes around 15 minutes.
• Gently roughen the outer roots so that they grow into the surrounding soil.
• If possible, dip the roots in a thin clay slurry; this holds moisture around them at the outset.

Planting hole and soil

• Dig a hole three times wider than the pot, loosen its sides and break up any compacted areas.
• Lighten heavy soil with about 20 per cent coarse sand or grit.
• Get the planting depth right: the crown should remain level with the soil surface, while lavender should sit roughly a finger-width higher.

Watering and mulching

• Water in thoroughly straight after planting: use about 10 litres per plant, even if it has rained.
• Apply a 7 cm layer of mineral mulch, such as lava rock or gravel. It reduces evaporation and warms up quickly.
• Avoid bark mulch: it stays wet for too long and uses up nitrogen as it decomposes.

“Golden rule: one very deep initial watering (around 10 litres) encourages deep roots – small amounts achieve nothing.”

Keep a watering can close by afterwards, but water only when the top hand-width of soil is dry and warm. The objective remains depth: water infrequently, but soak the soil thoroughly.

Missed April? How to rescue the project

Planting can often still succeed in April if you provide more support at the start. Choose the earliest possible date, opt for full sun, incorporate drainage material and keep emergency water available for the first summer. A hand test is useful: if the soil around the roots feels cool and slightly moist in the morning, hold off watering. When the temperature reaches 25°C or more in June, give young plants targeted water and briefly shield them from Föhn winds using horticultural fleece or a box.

A simple border plan that needs no hose

Keep the border layout clear. Perovskia and globe thistle provide structure at the back. Place Gaura and Sedum in the middle for movement and late-season interest. Lavender along the edge adds fragrance and definition. Geranium fills gaps and covers the ground. Use pale gravel throughout: it reflects sunlight and suppresses weeds.

Common mistakes – and how to avoid them

• Planting too deeply: the crown suffocates and rots, with lavender especially sensitive to this.
• Winter waterlogging: break up compacted ground early and watch for erosion.
• Applying too much nutrient-rich fertiliser: these perennials prefer poor soil, otherwise their stems lose stability.
• Too much fragmentation: plant a small number of species in groups to make maintenance easier and reduce water use.

Extra guidance: choosing mineral mulch correctly

Mineral coverings such as lava rock, grit or pale gravel work in two ways: they allow rain to penetrate without drawing capillary moisture into the air, and they keep the soil surface free from moss. A layer of 5–7 cm is enough. Beneath shrubs, 4 cm works well, while 7 cm around perennials stabilises the root area more effectively. Dark stones heat up more strongly; pale ones reflect light and keep the root zone cooler for longer.

Drainage check in 60 seconds

Dig a hole 30 cm deep and fill it with water. If it drains away within 30–60 minutes, drainage is suitable. If water remains after two hours, loosen the layer mechanically, mix in coarse sand or create localised drainage channels. For lavender, a 5–10 cm-deep layer of gravel beneath the root ball is worthwhile as a safety valve against winter wet.