Lilac care guide: when & how to prune, fertilize and spray

When: 3–7 weeks after the last spring frost.

• zones 3–5: about May 31 – Jun 28
• zones 6–7: about May 6 – Jun 3

This shrub sets next year's flower buds over the summer. Pruning within a few weeks after the flowers fade gives the most blooms next year. Prune later and you cut off the buds.

1. Wait until the last flowers have faded.
2. Remove dead, damaged and crossing branches first.
3. Renewal-prune: cut one-third of the oldest, thickest stems right down to the ground. Over three years this replaces the whole shrub with vigorous young wood.
4. Shorten overly long stems to an outward-facing bud or side branch to shape the shrub. Avoid shearing it into a ball.
5. Snap or cut off the spent flower clusters just above the next set of leaves. It tidies the plant, though it's optional for bloom.
6. Remove root suckers coming up away from the main clump.

Tools: Bypass pruners, Loppers

When: from 1 week before to 3 weeks after the last spring frost.

• zones 3–5: about May 3–31
• zones 6–7: about Apr 8 – May 6

A single spring feeding as growth starts covers most shrubs for the year.

1. Scatter fertilizer at the label rate from near the stems out past the drip line, where the feeder roots are.
2. Water it in thoroughly.

What to use: 🌿 Balanced organic granular fertilizer (e.g. Espoma Plant-tone 5-3-3) · 🌿 Low-nitrogen, high-phosphorus feed (e.g. bone meal or 5-10-10)

When: 3–8 weeks before the last spring frost.

• zones 3–5: about Mar 15 – Apr 19
• zones 6–7: about Feb 18 – Mar 25

This plant prefers a pH of 6.5–7.5. A soil test tells you whether you need lime, sulfur or extra nutrients, so you aren't guessing.

1. Take 6–8 small samples from the root zone, 4–6 in (10–15 cm) deep, using a clean trowel.
2. Mix them in a clean bucket, let the soil air-dry, and send about 2 cups to your local extension office or a soil lab. A home kit works but is less accurate.
3. Follow the lime or sulfur amounts in the report. Change pH slowly: no more than 1 unit a year.

Tools: Clean trowel, Plastic bucket, Soil test kit or lab mailer

When: 2–6 weeks after the last spring frost.

• zones 3–5: about May 24 – Jun 21
• zones 6–7: about Apr 29 – May 27

Mulch keeps roots cool and moist, suppresses weeds and slowly feeds the soil. Applying it after the soil warms lets roots wake up first.

1. Spread 2–3 in (5–7 cm) of mulch over the root zone.
2. Keep mulch 2–3 in (5–7 cm) away from stems and trunks. Mulch piled against bark invites rot and rodents.
3. Don't go deeper than 3 in (7 cm) in total. Too much mulch suffocates roots.

What to use: 🌿 Shredded hardwood or pine bark mulch