Calendula Growing Calendar: From Sowing to the Last Frost Flowers

The year at a glance

Calendula is a hardy annual that goes from seed to first flower in about eight to ten weeks and then, if it is deadheaded properly, flowers until frost blackens it. Everything below hangs off the sowing date rather than the calendar, which is what makes it portable between climates and hemispheres. The two decisions that shape the season are the hard cut back at midseason and the date you stop deadheading, which is the same thing as deciding whether next spring's bed is full of volunteers.

Late summer and autumn: the sowing most people skip

Where winter lows stay above about 20F (minus 7C), a sowing made in late summer or early autumn is the best calendula of the year. The plants germinate in warm ground, make a flat rosette before winter, sit through the cold without protection, and then grow away the moment the light returns. They flower four to six weeks ahead of anything sown in spring, on plants half again as large and far better branched.

Sow it the same way as a spring sowing but a little thicker, since winter takes some losses, and thin in early spring rather than in autumn. In colder gardens the same effect comes from letting a plant shed seed in autumn and keeping the volunteers, which is free. A cloche or a layer of row cover over the rosettes in the hardest weeks is worth having but is not usually necessary.

1. Sow once the summer heat breaks Ground below 75F (24C) and still warm enough to germinate quickly. Too early and the plants get too big before winter and rot.
2. Sow slightly thicker than in spring Expect to lose some rosettes to winter wet. Thin the survivors to 12 in (30 cm) as growth restarts in spring.
3. Leave the rosettes alone over winter Do not feed, do not water beyond natural rain, and do not tidy the leaves. A flat green rosette in midwinter is exactly right.
4. Keep autumn volunteers as a free crop Seed shed in autumn often germinates the same season. Those seedlings are the earliest flowering plants you will have, so do not hoe them off.

Overwintered plants flower on a bigger frame and mildew earlier as a result. Plan to cut them back hard at midsummer and they will give a second flush right through autumn.

Spring and early summer: sow, thin, and start deadheading

Spring sowing goes in as soon as the soil is workable, because calendula germinates in ground that is far too cold for most flowers and the seedlings shrug off a light frost. Cold soil means a fortnight or more at the vulnerable seedling stage in front of the slugs, so a cloche over the row is worth the trouble in an early sowing. Choose thin, free draining ground in full sun and do not improve it.

From emergence to the first bud, the plant needs almost nothing: a slug patrol for a week, one thinning pass to twelve inches (30 cm), and no feed at all. The first flower opens eight to ten weeks after sowing, and from that day the deadheading regime starts and does not stop. Aphids arrive on the buds at roughly the same moment, so start looking under the shoot tips once a week.

Midsummer: deadhead relentlessly, then cut back hard

This is the working half of the year. Go over every plant every two or three days and cut each fading flower stem back to the first good pair of leaves below it, which both prevents seed set and forces two new flowering shoots. Picking heads at their peak for drying does the same job, so harvesting and deadheading are one operation. Miss two weeks of this in high summer and the plant sets seed and shuts down.

When the lower leaves yellow, the stem bases go bare, the flowers come smaller and the first white mildew shows in the middle of the plant, cut the whole thing back to eight or ten inches (20 to 25 cm). Water it well the day before, clear every cut stem off the crown afterwards, and do not feed it. Three weeks later the plant is rebuilt and flowering again, and that regrowth carries it through autumn. This is the job most gardeners leave until it is too late.

1. Deadhead every two or three days Cut to a leaf pair, not to a stub. Include heads that are merely fading, because a drooping papery head is already setting seed.
2. Pick for drying at the peak Take fully open heads in the morning once the dew has gone. Every head picked is a head that cannot set seed and stop the branch.
3. Cut back on the signal, not on a date Yellow lower leaves plus bare stem bases plus the first mildew is the signal. Usually seven or eight weeks after the first flower.
4. Water before, clear debris after A watered plant regrows in a fortnight. Cut material left on the crown holds wet against the base and rots it.

If the summer is very hot, flowering pauses whatever you do. Time the cut back for the point where the heat breaks and the new growth arrives exactly as the cool weather returns.

Autumn: the best flowers, then the seed decision

Autumn is when calendula earns its place. The regrowth from the midsummer cut flowers heavily in cool weather, the color is deeper and cleaner than it was in high summer, and the plant keeps going through the first light frosts when little else in the garden is out. Keep deadheading through this flush and it does not stop until a hard frost blackens the whole plant overnight.

One decision cannot be deferred. Three or four weeks before you expect that hard frost, choose whether to keep deadheading or to stop. Stop, and the last heads ripen into rings of seed that drop straight down and give you a ring of early volunteers around each plant next spring. Keep going, and the bed comes up clean. Saving seed sits in between: leave two or three marked plants to ripen and keep picking from the rest.

Frost kills the plant but does nothing to the seed already lying in the soil. Clearing the blackened stems in autumn does not prevent next spring's seedlings if the heads were allowed to ripen.

The five dates worth writing down

Calendula runs on intervals rather than calendar dates, and those intervals belong to your soil and climate rather than to a seed packet. Five entries per plant give you the whole year: sown, emerged, first flower, cut back, and the date you stopped deadheading. Two seasons of that and you can plan continuous flowering from early summer to frost without guessing.

Add the position of every plant on a sketch of the bed, shade in the area you allowed to shed seed, and note which bed each sowing was in so that you keep the sowing moving around the garden. Next spring the sketch tells you where the volunteers will appear, which to keep and thin, and where the bare ground is that needs a fresh sowing.