Gadenin日本語Get the appWinter wet is what actually kills salvias
More salvias are lost to a wet winter than to cold. These plants tolerate frost and dry cold well, but a crown sitting in saturated soil for weeks at a time rots from below, and the plant simply fails to appear in spring. The gardener assumes it was not hardy enough. Usually it was hardy enough and drowned.
The symptoms are easy to read if you look at the right time. In late winter, scrape the soil back at the base of a suspect plant. A healthy crown is firm and pale inside with visible dormant buds. A rotted one is brown, soft and pulls away from the roots with almost no resistance, and often smells sour. There is no treatment at that stage.
Prevention is all in the planting. Set the crown slightly proud of the surrounding soil, work grit through heavy ground before planting rather than digging a single enriched hole, keep mulch two inches (5 cm) clear of the stems, and never leave a container standing in a saucer through the cold months. In a garden with genuinely heavy wet soil, growing the shrubby kinds in raised beds or large containers that can be moved under an eave for the winter is a more reliable answer than any amount of soil improvement.
| Symptom | Likely cause | Action |
|---|---|---|
| No regrowth in spring, crown brown and soft | Winter wet rot at the crown | Not recoverable. Replant in raised, gritty ground |
| A single stem goes limp and stays limp after watering | Rot at the collar from mulch or soil piled against the stem | Cut the stem out at the base; pull the mulch back from the crown |
| Gray-white dust on the upper leaf surfaces | Powdery mildew in still humid air | Thin the plant for airflow; water the soil, not the leaves |
| Shoots vanish overnight in spring | Slugs and snails on the emerging crown | Protect the crown for the first three weeks of regrowth only |
| Sticky shoot tips, distorted new growth | Aphids | A jet of water twice a week is normally enough |
| Ragged holes and pale spotting on leaves in summer | Capsid bug or leafhopper | Cosmetic. Tolerate it; the plant flowers regardless |
Powdery mildew in a still, humid summer
Powdery mildew shows as a fine gray-white dust on the upper surfaces of the leaves, usually starting on the lower leaves in the crowded middle of the plant where the air does not move. It is a disease of humidity rather than of wet leaves, which is why it appears in muggy weather and on plants squeezed against a wall or a hedge.
It rarely kills a salvia but it takes the plant out of the display, and badly affected leaves yellow and drop. The most effective response is mechanical: thin out crowded stems from the center of the clump to open the plant up, remove and bin the worst affected leaves rather than composting them, and stop overhead watering so the foliage is not damp at dusk. Space matters too, and a salvia given eighteen inches to two feet (45 to 60 cm) of clear air on each side rarely has the problem at all.
A plant that mildews badly every single year in the same position is telling you the position is wrong. Move it in spring to somewhere with more air movement rather than treating the symptom annually.
Slugs and snails, and why the danger window is short
The mature aromatic foliage of most salvias is of very little interest to slugs. The soft new shoots pushing out of the crown in spring are another matter entirely, and a clump can be grazed to nothing in two or three damp nights just as it is starting into growth.
The danger window is roughly the first three weeks of regrowth. Protect the crown during that period, clear away the old stems and any accumulated debris where slugs shelter through the day, and go out with a torch on damp evenings, which finds and removes far more of them than anything left on the ground. Once the shoots are six inches (15 cm) tall and the leaves have hardened and become aromatic, the problem stops on its own and nothing further is needed for the rest of the season.
Cuttings and young plants from the greenhouse are vulnerable for longer, because their foliage is soft. Keep newly planted salvias protected until they have made obvious new growth in the ground rather than assuming they share the toughness of an established clump.
The small stuff you can mostly ignore
Aphids cluster on the softest shoot tips in spring, leaving them sticky and slightly distorted. On a salvia this is rarely worth treating. A firm jet of water twice a week knocks them off, and the hoverflies and ladybirds that arrive within a fortnight finish the job. Spraying a plant that is about to flower costs you the bees and hummingbirds, which is a poor trade for a cosmetic problem.
Capsid bugs and leafhoppers produce ragged holes and pale stippling on the leaves in summer. The damage looks alarming when the leaf expands around the original puncture, but it does not affect flowering and there is no practical control worth applying in a garden.
Under glass, tender shrubby salvias overwintered indoors pick up whitefly and red spider mite, both of which thrive in dry warm still air. Keep the plants cool rather than warm through the winter, at around 45F to 50F (7C to 10C), inspect the undersides of the leaves once a fortnight, and remove the worst affected shoots. Cool storage is the single best preventive: warm winter quarters produce soft growth that is a magnet for both pests and gives you a weak plant in spring.
Keep a note of the first date you saw slug damage and the first date you saw mildew, along with which plants were affected. Both are strongly tied to position, and after two seasons the record tells you which spots in your garden are the problem rather than which plants.
Knowing when to give up on a plant
Salvias are not long-lived. The tender shrubby kinds get progressively woodier at the base, and after three or four years they carry fewer flowers on longer bare stems and no amount of pruning brings them back. The hardy border kinds thin out and die in the center of the clump over a similar period, leaving a ring of growth around a bare middle.
Both are signals to replace rather than repair. The shrubby ones are replaced from cuttings, which root so readily that there is no reason to nurse an exhausted parent. The hardy ones are lifted and divided in spring, the woody center discarded and the healthy outer portions replanted. Doing this every three or four years as a matter of routine keeps the planting vigorous and means you are never in the position of trying to rescue something that has already gone.
A plant that has been badly hit by winter should still be given until late spring before you dig it out. Salvias frequently look completely dead well after everything around them has started, and then push new shoots from the base once the soil genuinely warms. Scratch the base with a thumbnail first; if there is green under the bark, wait.