Gadenin日本語Get the appThe shape of the sweet alyssum year
Sweet alyssum is fast. About six weeks from emergence to first flower and four to seven days from sowing to emergence, which means the calendar is driven far more by heat than by any need for a long head start. That is the opposite of most bedding, and it changes how you plan the season: rather than one sowing in late winter, you make several small sowings through the year and time them around the heat.
The season divides into three parts. A first flush from late spring through early summer, which is the strongest and most fragrant. A midsummer stall when hot nights shut flowering down and the plant browns in the center. And a second flush from late summer to the first frosts, triggered by a shear back, which in a mild autumn is often the best display of the year.
In a cool summer with nights in the fifties Fahrenheit (10 to 14C), the middle stall may barely happen and the plant flowers continuously from late spring to frost with one tidying shear part way through. Where nights stay above 70F (21C) for weeks, the stall is long and unavoidable, and the sensible plan is to sow in early spring for a spring show and again in late summer for an autumn one, treating the hottest six weeks as time off.
| Stage | Timing | Main job | Watch for |
|---|---|---|---|
| Optional indoor sowing | 6 to 8 weeks before last frost | Surface sow uncovered, bright and cool | Leggy seedlings in poor light |
| First direct sowing | Once soil reaches 55F (13C) | Scatter on firmed damp soil, press, do not cover | Slugs and flea beetle on seedlings |
| Thinning | At 1 to 2 in (2.5 to 5 cm) tall | Thin to 6 to 8 in (15 to 20 cm) apart | Crowded plants rot at the base |
| Planting out young plants | Around the last frost date | Plant at the same depth, water in | Never plant the crown deep |
| Successional sowings | Every 3 weeks through spring | A short strip at a time | Sowing into ground that is already dry |
| First flush | Late spring to early summer | Water only in dry spells, no feeding | Overfeeding gives leaf and no flower |
| Midsummer shear | When it browns and stops flowering | Cut to half height, soak, half strength feed | Shearing a plant that is dry |
| Late summer sowing | About 10 weeks before first frost | Direct sow for an autumn display | Soil too hot and dry to germinate |
| Second flush | Late summer to first frost | Light watering, no further feeding | Gray mold in cool damp weather |
| End of season | At the first hard freeze | Leave one patch to seed, clear the rest | Clearing everything leaves no self-sown plants |
Spring: sowing and the first flush
If you want plants in flower the moment the frosts end, sow indoors six to eight weeks before your last frost date, on the surface of pre-watered compost, uncovered, at 60 to 70F (15 to 21C) in good light. Transplant in clumps of two or three at three or four true leaves, grow on cool at 55 to 60F (13 to 16C), and harden off over ten days. The plants can go out around the last frost date, since a light frost does no lasting harm.
For most gardens direct sowing is simpler and gives better plants. Wait for the soil to reach about 55F (13C), rake a fine level tilth, water it, scatter the seed thinly and press it down without covering. Keep the surface damp with a fine spray until the seedlings are an inch (2.5 cm) tall, then thin to six to eight inches (15 to 20 cm) apart. Do not skip the thinning; a crowded mat is the main reason established plants rot at the base later.
Sow a short new strip every three weeks through spring rather than the whole packet at once. Each sowing peaks for six to eight weeks, and staggering them means part of the planting is always in its best flush. This matters more if you are growing alyssum at the edge of a vegetable bed for the beneficial insects, since the point of it is to have flowers open continuously through the season.
The first flush arrives about six weeks after emergence and needs almost nothing from you. Water only in a genuine dry spell, do not feed plants in improved ground at all, and give container plants a half strength liquid feed once a month. Resist the urge to intervene; the commonest way to spoil this stage is to feed it.
Summer: the stall and the reset
When the plant browns in the middle and stops opening new flowers, shear it back to half its height in one even pass, soak the root zone thoroughly and give a balanced liquid feed at half strength. Water first if the soil is dry, because a shear on a dry plant produces nothing. New shoots break within five days and the plant is dense and budded again in ten days to a fortnight.
Stagger the cuts across a long edging or a series of containers so that some of the planting stays in flower while the rest recovers. Cutting everything on the same day leaves the whole bed bare for two weeks, which matters if you are relying on the flowers to feed hoverflies next to a vegetable crop.
Late summer is also the moment for the most useful sowing of the year. Sow direct about ten weeks before your first expected frost for plants that come into flower as the nights cool and everything else goes over. The difficulty is germination in hot dry soil, so sow into ground shaded by an existing crop if you can, water the strip before sowing, and keep the surface damp daily until the seedlings are up.
Do not shear later than about six weeks before your first expected frost. After that there is not enough warmth or daylight left for the plant to rebuild and flower, so you spend the end of the season looking at stubble instead of the autumn flush you would otherwise have had. A light tidy of straggling stems is fine at any time.
The dates worth recording each year are the sowing date of each strip, the date the first flower opened on it, and the date of each shear. Set against one another they show you next season whether to sow earlier, whether your shear came too late, and how long recovery actually takes in your own garden.
Autumn and the self-sown plants that follow
Sweet alyssum keeps going well past the point where tender bedding has blackened. A light frost damages open flowers but not the plant, and it will often open more once the weather warms again. Clear it after a sustained hard freeze, or leave it in place over winter in a mild climate where it behaves as a short-lived perennial, flowering through the cool months and stalling in summer instead.
Before clearing, leave one patch uncut and let it set seed properly. The flat rounded pods ripen and split, and the seed falls where it lies. Next spring you will find seedlings coming up in the gravel, in the joints between paving slabs, along the base of a wall and at the edge of the bed, generally in sharply drained spots that you could not have planted deliberately. Those self-sown plants are frequently better than anything you raise in a tray, because they germinate exactly when conditions suit them and their roots go straight down without a transplant check.
Managing them is a matter of editing rather than weeding. Pull out the seedlings that are in the way of something else and leave the ones that are not, thinning any dense patch to six inches (15 cm) apart so the survivors mound properly. Self-sown plants from a hybrid packet vary in color and habit from the parents, which is usually a pleasant surprise in a paving crack and a nuisance in a formal edging, so raise fresh seed for anything where uniformity matters.
This is also the point to review the season. Which positions kept flowering through the hottest fortnight, which corner browned first, whether the midsummer shear came early enough, and where the self-sown seedlings appeared. Sweet alyssum responds so directly to heat and drainage that a couple of seasons of specific notes about your own garden will improve your results more than any change of seed or feeding regime.