Quick facts
| Fact | Figures given |
|---|---|
| Habit | Annual, about 18 in tall at maturity (UMD); 12–18 in (Illinois); 'Spicy Globe' about 6 in tall and 12 in across (Wisconsin Master Gardener); 'Genovese' 3–4 ft (Clemson) |
| Sun | 6 or more hours of direct sun (UMD); 6–8 hours (Illinois blog, Arizona) |
| Growth temperature | Needs temperatures above 50°F to grow and does best in the 80s and 90s °F (Wisconsin Master Gardener) |
| First picking | About 6 weeks after planting (UMD); once plants are at least 6–8 in tall (Arizona) |
When to plant: warm nights, warm soil
Every source waits until frost danger has passed. Several add a temperature test:
- Nights above 50°F. Direct-sow once night temperatures stay above 50°F (Iowa State); transplant when days are consistently in the 70s and nights above 50°F (Clemson).
- Soil at least 60°F. Set transplants out after the frost-free date, in soil of at least 60°F; cold soil and air can stunt growth (Illinois).
- Two weeks after last frost. UNH's planting table sets basil transplants out 2 weeks after the last frost; for central New Hampshire it treats Memorial Day as a conservative last-frost estimate.
Find your dates on frost dates explained, then count back with the planting calendar.
Starting seed indoors
- Start 3–8 weeks before setting out, depending on the source (table below).
- Sow ¼ in deep (Clemson, Arizona) or ½ in (Wisconsin), 2–3 seeds per pot (Wisconsin).
- Keep the mix warm: about 75°F (Iowa State), at least 70°F (Illinois). Expect sprouts in 5–7 days (Illinois, Wisconsin, Arizona) or 5–10 days at 70°F (Clemson).
- Give seedlings bright light so they do not stretch; leggy seedlings transplant poorly (Iowa State).
- Pot up or transplant after two sets of true leaves (Clemson, Arizona).
Spacing and containers
| Source | Spacing |
|---|---|
| Arizona | 6–12 in apart |
| UMD | 12 in in the row, 18 in between rows |
| Wisconsin Master Gardener | 12–15 in |
| Clemson | 2 ft between plants, 3 ft between rows (16 plants per 100 sq ft) |
| Illinois (2020 blog) | At least 2 ft, for air circulation and less disease |
Wider spacing is also the main cultural defense against downy mildew (below). For grid beds, see square foot gardening spacing.
- Pot size. UMD puts basil in its smallest class: at least 1–3 gal of mix, 4–6 in deep. More crops: container sizes for vegetables.
- Drainage. Use a pot with a drainage hole and a well-drained potting mix; pots dry out faster than beds (Arizona, Illinois blog).
- Compact types. Dwarf types such as Bush or Greek suit containers (Iowa State); UMN lists Prospera Compact DMR as suited to containers.
- Indoors. Several seeds in a small pot in full sun can be picked in about 4–5 weeks; re-sow every 2 weeks for a steady supply (Illinois).
Pinching and harvest
- 1. Cut the whole stem just above a pair of leaves (Illinois blog, Arizona)
- 2. New shoots grow from that leaf pair; new growth appears within about a week (Illinois blog, Arizona)
- 3. Flower buds: remove as soon as they appear for the best leaf flavor (Clemson, Illinois)
- 4. Leave at least half of the plant in place (Illinois blog)
- 5. Top of a leaf with downy mildew: yellow areas bounded by the major veins, later turning brown (Cornell, UMN, Clemson)
- 6. Underside of the same leaf: purplish-gray, fuzzy spores behind the yellow areas; look early in the morning (Cornell)
- Pinch early. Pinch stem tips as stems lengthen for a bushy, compact plant (UMD); Iowa State pinches in mid-spring and again later in the season.
- Cut above a leaf pair. Cut the whole stem just above a pair of leaves and leave at least half the plant; new growth appears at the cut within a week (Illinois blog, Arizona).
- Pick tips often. Pinch branch ends with one or two sets of leaves (Clemson, Wisconsin), and leave enough foliage that growth is not much reduced (Clemson).
- Remove flower buds as soon as they appear (Clemson, Illinois); flowering and seed set make the plant woody and the leaves bitter (Illinois blog, Arizona).
- Renew woody plants. When stems turn woody and stop producing, cut the plant back by a third (Wisconsin).
Pick in dry weather: gray mold enters fresh harvest cuts, which heal by 48 hours (Clemson). Avoid heavy fertilizing, which reduces flavor (UMD, Iowa State).
Cold damage
- Chilling. Leaves can be damaged and turn black at 50°F (Illinois). Harvested fresh basil is damaged by chilling below 40°F (UMass).
- Frost. Frost turns leaf tissue black; when frost is forecast, cover plants completely or make a final harvest (Wisconsin). For a late spring frost, cover with pine straw, inverted pots or buckets (Clemson).
- Overwintering indoors. Before the first fall frost, cut plants back, pot them and set them in a sunny window (Clemson); this extends the season by about a couple of months (Illinois blog).
Basil downy mildew
Basil downy mildew is caused by Peronospora belbahrii (Cornell), a water mold rather than a true fungus (UMN). It was first reported in south Florida in October 2007 and across the eastern US in 2008; spores travel on the wind each summer, and the pathogen is also seed-borne (Cornell).
| Question | What sources say |
|---|---|
| First sign | Yellowing on the upper leaf surface, limited by the major veins (Cornell, UMN, Clemson); it can look like a nutrient deficiency (Clemson). Infection starts on lower leaves and moves up (UMN) |
| Confirming it | Purplish-gray, downy spores on the underside, opposite the yellow areas; they form overnight, so look early in the morning (Cornell). |
| Later | Brown or black spots and dying leaves (Cornell, Clemson, Iowa State) |
| Favored by | Leaf wetness, dew and high humidity overnight (Cornell); infects at temperatures as low as 59°F and is often worst in late summer (UMN). Canopy humidity below 85% suppresses it; infection stops above 80–88°F (Cornell) |
| Eating leaves | Leaves from infected plants are safe to eat (UMD) |
Cultural controls
- Plant resistant varieties, the best prevention (UMN).
- Choose full sun and good air movement; space plants widely (Cornell, UMD, Clemson).
- Keep leaves dry: drip irrigation (Cornell); no overhead or nighttime watering (Iowa State); with sprinklers, water deeply and infrequently, early on a sunny day (UMN).
- Move potted basil indoors overnight during humid or rainy spells (UMN, Cornell).
- Check seedlings and transplants (UMN). Bag and remove infected plants at once (UMD, Iowa State), ideally on a sunny day, since sunlight kills the disturbed spores (Cornell).
- If plants are lost, sow fresh seed in containers or elsewhere in the garden (UMD).
Resistant and less susceptible varieties
| Group | Names given | Notes |
|---|---|---|
| Rutgers DMR sweet basils | Devotion, Obsession, Passion, Thunderstruck (Cornell, UMN, Iowa State) | High resistance, released from 2018; some symptoms still develop (Cornell) |
| Prospera series | Prospera CG1, ILL2, PL4, PS5, Red DMR (Cornell); Prospera Compact DMR (UMN) | Very few symptoms in Cornell trials, but a newer race has overcome its resistance gene in some places, including Long Island (Cornell) |
| Amazel, Pesto Besto | Same resistance source as Prospera (Cornell) | Amazel is sold as cuttings because its seed is sterile; Pesto Besto grows from seed (Cornell) |
| Moderate resistance | Emma, Everleaf (Cornell) | — |
| Other basil types | Red, lemon, lime, Thai and spice types (Cornell, UMN, Iowa State) | Fewer symptoms than sweet basil, but different flavor (Cornell); Genovese is among the most susceptible (UMN, Iowa State) |
Resistance is not immunity (Cornell). This page gives no fungicide advice: UMN says the products available to home gardeners are not effective. Ask your county extension office to confirm a diagnosis.
Where sources disagree
| Topic | Figures |
|---|---|
| Weeks to start indoors | 6–8 (UNH); 4–6 (Clemson, Wisconsin); 4–5 (Iowa State); 3–4 (Illinois) |
| When to set out | After frost (UMD); nights above 50°F (Iowa State, Clemson); soil at least 60°F (Illinois); 2 weeks after last frost (UNH) |
| Does downy mildew persist? | Resting spores can persist in plant material for several years (Iowa State) vs no resting spores form in the US, so it cannot overwinter in Minnesota (UMN) and does not survive without living plants (Cornell) |
| Storing fresh basil | Stems in water at room temperature; refrigeration discolors leaves (Illinois) vs refrigerate in perforated plastic bags (Iowa State); keeps only a few days in the refrigerator (Wisconsin) |
Small-space checklist
- Wait for frost-free weather and nights above 50°F before planting out.
- Start seed indoors 4–6 weeks ahead in warm mix, about 70–75°F.
- Give each plant 6–8 hours of sun and 1–3 gal of mix in a drained pot; choose a DMR variety.
- Cut stems just above a leaf pair; leave at least half the plant.
- Water at the base, early in the day; check leaf undersides in the morning.
- Harvest or cover plants before frost.
More crop pages: tomatoes, peppers, lettuce, cucumbers and potatoes.
Sources
- University of New Hampshire Extension — Growing Vegetables: When to Plant Your Vegetable Garden (fact sheet)
- University of Maryland Extension — Growing Basil in a Home Garden (updated 2026)
- University of Maryland Extension — Downy Mildew on Basil (updated 2023)
- Cornell University, Cornell Vegetables — Basil Downy Mildew (Margaret Tuttle McGrath; prepared for Vegetable MD Online, updated March 2023)
- University of Minnesota Extension — Basil downy mildew (Schuh and Grabowski, reviewed 2022)
- Iowa State University Extension and Outreach, Yard and Garden — Growing Basil in the Home Garden (reviewed 2025)
- University of Illinois Extension, Herb Gardening — Basil
- University of Illinois Extension, Flowers, Fruits and Frass — Growing Basil in Your Backyard (Brittnay Haag, 2020)
- Wisconsin Master Gardener Program, UW–Madison Extension — Basil, Ocimum basilicum (2003, PDF)
- Clemson Cooperative Extension Home & Garden Information Center — Basil (HGIC 1327, Joey Williamson, updated 2019)
- University of Arizona Cooperative Extension — Basil (Backyard Gardener #245, Jeff Schalau, 2024, PDF)
- UMass Amherst Center for Agriculture, Food, and the Environment — Basil (vegetable fact sheet)
- University of Maryland Extension — Types of Containers for Growing Vegetables
All sources were opened and checked in October 2026. Rules and figures change; confirm with the original before acting.