How to grow Arenaria
Arenaria is a popular choice for crevices, walls, and rockeries, and is known for its dense, ground-hugging mat of evergreen foliage which becomes smothered in small white or pink flowers from late spring. A vigorous growth habit means it is quick to form mounds which, when given the opportunity, will cascade elegantly over an edge.
Arenaria is also known by the common name of sandwort.
Key Information
Position
Soil Conditions
Hardiness
Where & when to plant Arenaria
For best results, plant in spring once all risk of frost has passed in your area. This varies from region to region though tends to be around late May. Planting at this time gives these drainage-loving plants a growing season’s worth of root growth before being faced with the wet conditions of winter. If you acquire arenaria plants at other times of year, it can be worth potting them up using a free-draining mix and growing on somewhere sheltered until the following spring.
When the time is right, arenaria suits rockeries, walls, paving crevices, and path edges. It can also be grown in a permanent container or stone trough filled with a free-draining compost mix.
How to plant Arenaria
- For planting in the ground, clear the chosen area of weeds.
- Unless you already have poor, sandy soil, now is the time to improve drainage by digging in some horticultural grit or sharp sand.
- Dig a planting hole several times larger than the root ball.
- Place the plant in the hole, ensuring the top of the root ball sits level with the surface of the soil. Too low and the plant may rot, too high and the roots can dry out.
- Backfill with soil and firm in gently.
- Soak well with water.
- Mulch with horticultural grit.
- For planting into a wall or crevice, simply excavate as large a cavity as you can, loosely fill with a sandy soil or compost mix, and push the small plant in. Compress with your fingers so that it holds tight, and thoroughly wet the soil/ compost with a gentle spray of water.
- For planting in containers, first choose an appropriate container, ensuring there are plenty of drainage holes. Arenaria grows quickly, so choose a pot which is roughly the same width as the expected eventual size of the plant.
- Use a good quality potting compost with a high ratio of horticultural grit mixed in (aim for around 40% grit), and, if not already present in the compost (check the description on the bag) some slow-release fertiliser granules.
- Start by partially filling the pot with compost; enough so that when placed on it the upper surface of the root ball is about 3cm lower than the top of the pot.
- Infill all the space surrounding the root ball with compost, firming down with your fingers then adding a little more so the plant is held tight.
- Pick up the pot (if you can) and lightly tap on the potting bench or ground a few times to help further settle the compost around the plant.
- Soak well with water.
- A mulch with horticultural grit will look attractive and help to prevent a ‘cap’ or crust forming on the top of the compost (something container plants can suffer due to the artificial nature of their watering).
What to plant with Arenaria
We particularly love seeing the brilliant yellow flowers of acacia combined with purple-blues and zingy lime greens. If you have the sunny, protected spot needed to grow this tree outside, you could go for the half-hardy climbers hardenbergia and sollya, perhaps with a generous clump of euphorbia as lower storey planting.
How to care for Arenaria
Pruning and Deadheading
No pruning is necessary for this fabulously low-maintenance, self-sufficient plant.
A very light trim after flowering will keep the plant looking tidy, though is by no means essential.
Watering
Water newly planted arenaria regularly until established (i.e., the first few weeks in the ground), and then only in very hot dry spells after this. From year two onwards, arenaria is known to be drought tolerant.
Container-grown arenaria will need watering throughout every growing season. Aim to water deeply and thoroughly, then allow the compost to almost dry out completely before repeating. This is to avoid having the roots sitting too wet, something these drainage-loving plants dislike.
Feeding
Arenaria hails from naturally poor soil, so does not usually need any extra fertiliser when grown in the open ground.
Those in containers may, over time, benefit from some slow-release, low-nitrogen feed. Either mix this into the compost when potting/ repotting or apply as a ‘top dress’. This means scraping away the top 5cm of compost in a container and replacing it with a fresh mix containing a small amount of feed. Aim to carry this out in spring.
Cold Protection
Arenaria are hardy and, if grown in the right conditions (i.e., sunny and free draining), should withstand an average UK winter without the need for any additional protection. Having said this, there are varying degrees of hardiness, and it’s worth being aware of the differences between species.
Those with a hardiness rating of H4 can cope with temperatures dipping to between -5°C and -10°C, so may struggle further north or in very harsh winters, particularly if drainage is poor and the roots spend time sitting in wet soil. They make more vulnerable container plants, and it can be a good idea to wrap their pots in bubble wrap, fleece, or hessian to protect the roots against frost.
Arenaria with an H5 rating can withstand between -10°C and -15°C and should be fine in all but the most exposed spots. Again, protect those grown in containers.
Pests and Diseases
Arenaria is considered problem-free.
How to propagate Arenaria
The quickest and easiest way to propagate arenaria is by lifting and dividing established clumps in spring. As well as providing new plants this has the added benefit of reinvigorating existing clumps. Allow 2-3 years between each division so the plant can sufficiently re-establish.
- Choose a day when the soil is not frozen or waterlogged.
- Dig the plant out of the ground.
- Shake off any excess soil.
- Separate the plant into sections using either swift, cutting blows with a sharp spade, or two forks inserted back-to-back with tines touching, handles then pushed together to prise the plant apart.
- Discard old, damaged, or surplus pieces, keeping healthy, vigorous material.
- Replant decent-sized pieces where desired, and any smaller bits can be potted up.
- Water well until fully established.
* Many plants carry Plant Breeders Rights and cannot be propagated for commercial purposes.
Common Arenaria questions
- Does arenaria spread?
montana and A. purpurascens form neat, self-contained cushions or mounds. A. balearica has a more spreading, mat-forming habit and can keep going beyond its average width of 30cm if the opportunity arises. Having said this, it is very easily controlled and is not considered invasive. - Do you cut back arenaria?
Arenaria does not need cutting back and is best left to its own devices. A very light trim can be done after flowering if you would prefer to tidy away the spent flowers.
- Is arenaria hardy?
Provided it is given sufficient drainage, arenaria should survive an average UK winter without any problems. See our ‘Cold Protection’ section above for more detailed information.