Mat formers are plants that will cover an area by sending out branches that quickly develop short surface roots. Overall height is low, under 5cm. Having such short stature, many of these plants are able to hold foliage all year and provide some off-season texture and colour for the rock garden. There is also an ability to cover and conform to the contours of rocks, thus softening hard edges and tying together the garden. If we consider dwarf shrubs and conifers to be the backbone of the rock garden, then mat formers are the skin. With the relatively shallow root structure, other taller, deeper-rooted plants can be grown through mats.
There are three things to consider:
- The mat former will provide an excellent background or foil to show off the specimen plant.
- The mat will provide a cooler root run for the specimen and also a drier condition for the crown. In the case of bulbs the mat fills an otherwise empty space for the dormant period of the bulb, and aids in drying and ripening the bulb.
- Intergrowing of mats can provide some interesting and beautiful combinations. Try it!
And now to the list of a dozen plants we have found particularly useful.
1. Alyssum propinquum- The Turkish alyssums in section caespitosum are not well known. Making dense mats of gray/green they are tolerant of heat and cold. Mostly spring flowering, they do resume growth and blooming from September onwards, staying evergreen through the winter and often retaining flowers through the snow. Very effective in combination with acantholimons and dianthus.
2. Paronychia spp.- Curious mats as tight as the smaller thymes and just as tough. P. serpyllifolia is from S. Europe. It can be used between paving stones and will withstand moderate traffic. The translucent flower bracts are petal-like in appearance, effecting a longer period of bloom. New to culture is p. sessiflora from the Rockies. Very strange looking with rock hard mats of prickly needles, with tiny greenish/yellow flowers. Slower in growth, but able to grow under very dry conditions.
3. Delosperma sp. 'Reznicek'- For a change of pace, try a succulent. From South Africa, this delosperma is a higher, cold hardy collection. Mats of dense, dark engorged needles; sessile, white-eyed yellow flowers. The South African mountain flora contains a lot of succulent plants. The desert was essentially lifted up over millennia, the plants adapting to their new conditions. Hence, even though succulent, they tolerate moister conditions. D. sp. 'Reznicek' has been the best growing cultivar we have grown.
4. Coluteocarpus vesicaricus- An extraordinary crucifer, c. vesicaricus makes taller cushions (5cm) of androsace-like rosettes. Large, fragrant, 4-petalled flowers are followed by inflated fruits of pale, papery green. The fragrant flowers and show-stopping fruits make for a spectacular plant.
5. Eunomia oppositifolia- A favourite for its slate-coloured, round leaves on wiry stems. Dark terminal buds, which erupt in fragrant cushions of, light lilac/pink often just after the snow leaves. A slow mat former, particularly effective in troughs amongst tufa.
6. Globularia repens- Really a tiny subshrub as its stems are quite woody. The dark green, leathery leaves are an attractive mat, whether for its own miniature round heads of deep blue flowers or for crocus or corydalis growing above.
7. Thymus serpyllum 'minus'- The most rugged form of thyme which easily grows in pavement crevices and creeps over the edges. It will withstand traffic better than anything else we have used. Flowers are spare; but the rich pink is eye-catching over the soft gray-green.
8. Veronica spp.- In particular v. oltensis and v. liwanensis form mats of dark green rapidly. Easy to control, one simply rips it back without any resentment from the plant. Lovely blue and white flowers give a hazy effect in May.
9. Hetrotheca jonesii- Prostrate woody stems clothed in gray. Another show stopper, as the leaves just seem to glisten. Clear, yellow flowers on terminal stems are borne all summer and into November here. Also capable of creeping over rocks and conforming to the contours.
10. Scutellaria prostrata- Scutellaria are frequently ignored- they are largely deciduous, and really don't come into their glory until late May. S. prostrata is truly handsome with its maroon flowers in June when the spring flush is fading. With its deciduous habit, it is also well behaved.
11. Erigeron scopulinus- Not your usual erigeron, this micromat slowly inhabits a space with its tiny linear leaves. Exquisite little white daisies dance just above the very low mat.
12. Arenaria tetraquetra- Rock hard mats of green and silver tetragonus leaves, even more congested is the subspecies granatensis. Both forms are suitable for troughs. Stemless white flowers in May add to the show. A great plant to intergrow with others.
(2006 Catalogue Introduction)