Today we’re visiting with Mariel Tribby. Mariel does most of her gardening at her job at the Missouri Botanical Garden in St. Louis, where she is in charge of the rock garden. She is also a board member of the North American Rock Garden Society, and she grows a lot of cool rock garden plants. Sometimes these plants have a reputation for being difficult to grow, but mostly they just need good drainage and good plant choices. The St. Louis area has hot, humid summers and pretty cold winters (Zone 6), but Mariel cultivates lots of great plants that love those conditions.

Note: A lot of these plants are so uncommonly grown that there isn’t a lot of information on winter hardiness, so many of the Zone rankings below are educated guesses.

This Campanula formanekiana (Zones 6–8) is just loaded down with flowers! The species generally grows as a biennial, so this explosion of blooms may be its swan song before leaving the garden, but wow, what a beautiful display!

A fly visitor is pollinating this Aristolochia tomentosa (Zones 5–8). Aristolochia’s odd flowers lure in flies with colors—and sometimes smells—that trick them into thinking the flowers are carrion that they can lay their eggs on. Once a fly crawls into the flower, backward-pointing hairs keep it trapped; as it buzzes around, it gets covered with pollen. It is only released when another fly enters that already has pollen from another flower on it. That pollinates the flower and causes the hairs to collapse, releasing the pollen-covered fly to go off and pollinate the next flower.

Globularia punctata (Zones 3–8) looks beautiful in the morning light. This plant forms a low cushion or carpet with these blue blooms in spring.

Penstemon cobaea (Zones 5–8) is in full bloom. There are nearly 300 different species of penstemon, native mostly to western North America, and many of them are beautiful additions to the garden. Most, but not all, require well-drained soil to thrive.

Mariel says she’s a big fan of Dracocephalum ruyschiana (Zones 3–7), as it is easy to grow and not overly vigorous or aggressive, despite being in the mint family.

There is a whole world of little rock garden irises. This is Iris timofejewii (Zones 4–8) with the bright yellow Aurinia saxatilis (Zones 3–7) behind it. What an amazing color combination!

Pulsatilla (Zones 4–8) emerge with their incredibly fuzzy new leaves and flowers early in the spring. These emerged so early that they caught a dusting of late snow on their blooms.

Campanula baumgartenii (Zones 4–8) and Silene schafta (Zones 3–9) grow together in a tapestry of cheery blooms.

If you want to see more from Mariel, check out her Instagram: @rockeryplantess

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