Idaho Lawn Care Calendar 2026: Fall & Spring Task Dates

Why: Stops winter annual weeds — annual bluegrass (Poa annua), henbit, chickweed — from germinating as soil cools through 70°F.

How: Apply prodiamine or dithiopyr at the label rate when soil at 2–4 inches drops toward 70°F for several days, then water in ½ inch. Skip it on any lawn you plan to seed this fall — pre-emergent blocks grass seed too.

Rule: Cool-season: 60–30 days before first frost. Warm-season: 75–45 days before first frost. · full guide →

Why: Tropical houseplants are damaged by nights in the 40s, well before any frost — and a sudden move from 50°F nights to a 70°F house causes leaf drop.

How: Start when night lows dip below 50°F. Inspect and rinse foliage, treat for pests (insecticidal soap, and a soil drench or repot for fungus gnats), then move plants to a bright window over a week, starting with a few nights indoors. Cut watering back by half once inside.

Rule: 3 weeks before first frost until a few days before (when nights fall below 50°F).

Why: Relieves compaction and opens thatch so water, air, and fertilizer reach the roots — and it is the best seedbed prep for overseeding.

How: Use a core (plug) aerator, not spikes, on moist soil — two passes at right angles, 20–40 holes per square foot. Leave the plugs to break down. Cool-season lawns: early fall during active growth. Warm-season lawns: late spring to early summer when bermuda and zoysia are growing hardest.

Rule: Cool-season: 7–3 weeks before first frost. Warm-season: 8–15 weeks after last spring frost. · full guide →

Why: Warm soil plus cool air is the best germination combination of the year, and new seedlings need 6–8 weeks of growth before the first hard freeze.

How: Mow low, rake or dethatch so seed touches soil, core-aerate if you can, then spread seed (tall fescue 6 lb, bluegrass 2–3 lb, perennial rye 6–8 lb per 1,000 sq ft). Water lightly twice a day for two weeks. Warm-season lawns only overseed with annual/perennial ryegrass for winter color.

Rule: Cool-season: 7–4 weeks before first frost. Warm-season (ryegrass): 6–3 weeks before first frost. · full guide →

Why: A cover crop holds soil, scavenges leftover nitrogen, and adds organic matter over winter — bare vegetable beds lose both soil and fertility to winter rain.

How: Broadcast cereal (winter) rye at 2–3 lb per 1,000 sq ft into cleared beds, rake in ¼–½ inch, and water. Rye germinates down to 34°F soil, so it is the last-chance cover crop; mix in crimson clover or hairy vetch if you have 4+ weeks before frost. Mow and turn under 3–4 weeks before spring planting.

Rule: 6–2 weeks before first frost (rye itself can go in right up to frost).

Why: Fall nitrogen builds roots and carbohydrate reserves instead of top growth — the single most valuable feeding of the year for cool-season turf.

How: Cool-season lawns: 0.75–1 lb of actual nitrogen per 1,000 sq ft, slow-release, with a soil test deciding phosphorus and potassium. Warm-season lawns take their LAST nitrogen on a calendar cutoff, not a frost countdown — mid-August across most of the South (Clemson: no nitrogen after August 15, coastal September 1; UGA: nitrogen through mid-August; LSU AgCenter: nothing after the end of August), and September in Florida and Texas. Late nitrogen on bermuda or centipede invites winterkill and large patch.

Rule: Cool-season: 4–1 weeks before first frost. Warm-season: last nitrogen of the year by mid-August to mid-September — an extension calendar cutoff, not a frost offset. · full guide →

Why: Garlic needs 4–6 weeks to root before the ground freezes but should not push much top growth — planting around the first frost, 2 weeks either side, is the sweet spot.

How: Break bulbs into cloves the day you plant. Set cloves pointy end up, 2 inches deep (3 in cold zones), 6 inches apart, in full sun and loose, compost-rich soil. Mulch 4–6 inches of straw in cold climates. Hardneck varieties (Music, German Extra Hardy, Chesnok Red) for the North; softnecks (Inchelium Red, California Early) for the South, where they need little or no chilling.

Rule: Cool/transition: 2 weeks before to 3 weeks after first frost (before the ground freezes). Warm South: 2 weeks before to 3 weeks after first frost. · full guide →

Why: Grass left long under snow mats and invites snow mold; cut too short it loses winter insulation. The last cut at 2–2.5 inches is the compromise.

How: Keep mowing as long as the grass grows (it slows sharply below 50°F). Drop the deck one notch on each of the last two mows so the final height is about 2–2.5 inches for cool-season turf. Mulch the last leaves into the lawn rather than bagging.

Rule: 1 week before to 2–3 weeks after first frost, when growth stops.

Why: Water left in lines and backflow preventers expands when it freezes and splits pipes, valves, and heads — a repair that costs more than the whole winterization.

How: Shut the supply valve, drain or blow out each zone with compressed air (50–80 psi for poly pipe, never more), open the test cocks on the backflow preventer, and set the controller to "off" (not "rain delay"). Do it before the first HARD freeze (28°F), which typically follows the first frost by 1–3 weeks.

Rule: From just before first frost until first hard freeze (~2 weeks later).

Why: Bulbs root in cool soil and need 12–14 weeks of chilling below 45°F to flower — planted into warm soil they rot or sprout early.

How: Plant when soil at 6 inches falls below 55°F: tulips and daffodils 6–8 inches deep, 4–6 inches apart, pointy end up, in well-drained soil. Water once, then leave them. Zones 8 and warmer: pre-chill tulips 10–12 weeks in the refrigerator (away from fruit) and plant in late November or December.

Rule: Cool/transition: 1 week before to 5 weeks after first frost. Warm South: 2–8 weeks after first frost with pre-chilled bulbs. · full guide →

Why: Crabgrass germinates when soil at 1–2 inches holds 55°F for 4–5 consecutive days. Pre-emergent has to be in place BEFORE that — it has no effect on crabgrass that has already sprouted.

How: Watch soil temperature, not the calendar: apply prodiamine, dithiopyr, or pendimethalin as soil approaches 55°F (forsythia bloom is the old signal). Water in ½ inch within 48 hours. Dithiopyr also controls crabgrass up to about the 2-leaf stage if you run late. Do not apply where you will seed within 3–4 months.

Rule: Cool-season: 3 weeks before to 1 week after last spring frost. Transition: 4 weeks before to just before last frost. Warm-season: 5–1 weeks before last frost. · full guide →

Why: The first cut removes winter-damaged tips and signals the lawn to tiller and thicken — but mowing soggy soil ruts it, and scalping stresses turf before roots are working.

How: Mow when grass reaches about 3 inches and the soil is firm underfoot, taking off no more than a third of the blade. Sharpen the blade first. Warm-season lawns: one low "scalp" mow at green-up removes dead top growth and speeds warming of the crowns — bag those clippings.

Rule: Cool-season: 2 weeks before to 1 week after last frost. Warm-season: 1 week before to 3 weeks after last frost.

Why: Spring seeding is second-best (fall is better) because seedlings face summer heat and crabgrass, but it is the only window for warm-season seed, which needs 65–70°F soil.

How: Cool-season seed germinates from 50°F soil — seed as early as the ground can be worked and skip pre-emergent on that area (or use mesotrione, which is safe on new seedings). Warm-season seed (bermuda, zoysia, centipede, buffalograss) waits for 65°F+ soil, typically late spring. Keep the top ½ inch moist until established.

Rule: Cool-season: 1 week before to 4 weeks after last frost. Warm-season: 6–12 weeks after last frost.

Why: Feeding too early pushes leaf growth ahead of root growth and feeds weeds — wait until the lawn is actively growing and has been mowed 2–3 times (cool-season) or is fully green (warm-season).

How: Cool-season: a light feeding (0.5–0.75 lb N per 1,000 sq ft) in late spring; the heavy feeding belongs in fall. Warm-season: wait until bermuda, zoysia, or St. Augustine is 100% green, then 1 lb N per 1,000 sq ft; centipede gets half that, once. Never fertilize dormant warm-season turf.

Rule: Cool-season: 2–6 weeks after last frost. Warm-season: 6–10 weeks after last frost (full green-up).