Basil

Start basil indoors three to four weeks before your last frost

Sow seed in flats three to four weeks before your frost-free date and hold the mix at 70 degrees F or above. At that warmth seed germinates in about five to seven days, and the seedlings reach plantable size right about when the garden is warm enough to take them. Field basil runs 60 to 85 days from seeding or transplant to first cut (Rutgers FS1279), so in short-season zones a direct-sown plant spends its best weeks as a seedling. Started early, it goes out already branching. Basil also germinates and grows poorly below 70 degrees, which a spring seedbed rarely offers.

Wait for 60 degree soil and 50 degree nights before planting out

Set plants out well after your frost-free date, once soil is at least 60 degrees F and nights stay above 50 degrees F. Space plants 6 to 12 inches apart in the row (Rutgers FS1279). If a cold night is forecast, wait - a week in the flat costs less than a check in the field. Basil is tropical and takes cold injury far above freezing: Illinois Extension reports cold soil and air stunt growth and blacken leaves at 50 degrees F. A plant chilled at transplant sulks for weeks and never catches the one set out warm.

Water the soil, not the leaves, and do it early

Give about 1 1/2 inches of water per week (Utah State Extension). Use drip or a wand at the base of the plant, and water deeply and infrequently early on a sunny day so any splashed foliage dries quickly. Never leave basil going into evening with wet leaves. Downy mildew needs liquid water sitting on the leaf to infect, and it sporulates in overnight humidity. Dry leaves at nightfall break the cycle, which is why airflow and drip do more for basil than any product a home gardener can buy.

Feed lightly once you start cutting, and no more

If a soil test shows fertilizer is warranted, work it into the top 6 inches before planting; if using compost, apply no more than 1 inch of well-composted organic matter per 100 square feet. Once plants reach the harvestable stage, sidedress with an organic or all-purpose liquid nitrogen source at 1 to 2 tablespoons every 2 to 3 weeks per 10 feet of row. Basil in pots needs feeding weekly, because watering flushes the nutrients out. Each cut removes leaf the plant has to rebuild, and basil responds to nitrogen. Keep it to a light, repeated feed rather than one heavy push - and site the plant in full sun, which Utah State notes gives more essential oils and better flavor than shade.

Pinch flower buds the day you see them

As soon as flower buds form at the stem tips, pinch them out along with the top set of leaves. Keep doing it through the season. Pinching stem tips on young plants the same way builds a bushy plant with more leaf. Once basil turns to flowering it stops putting energy into leaves, and the leaves it has already made turn bitter and the stems go woody. The bud is the switch, so you catch it at the bud.

Downy mildew: turn the lower leaves over every week

Through warm humid weather, check the undersides of the lowest leaves weekly, in the early morning. You are looking for pale yellow blocks between the veins on top and velvety purple-grey fuzz underneath. Pull and bag infected plants immediately, and harvest heavily off healthy ones while you still can. Peronospora belbahrii is a water mold whose spores blow in on summer wind and sporulate on wet leaf undersides overnight. It moves from the bottom of the plant upward and can take the whole planting, so the only cheap moment is the first leaf.

⚠ Do not reach for a spray here: extension testing finds the fungicides available to home gardeners are not effective against this pathogen, because it is a water mold rather than a true fungus. Resistant varieties, spacing and dry leaves are the real controls.

Leave four sets of leaves standing on every cut

Harvest by pinching branches or leaves, or cut with sharp scissors or a knife, taking stems back to just above a pair of leaves. Always leave at least four sets of true leaves on the plant. Field basil runs 60 to 85 days from seeding or transplant to first cut, then re-cuts through the season. New shoots break from the buds in the leaf axils you leave behind, so the stub you leave is the next harvest. Cut too low and there are no buds left to regrow from.