Gadenin日本語Get the appFast growth is the whole objective
Everything you do to an arugula plant should be aimed at keeping it growing without a check. A crop that runs from sowing to harvest in four to six weeks with no interruption gives broad tender leaves with a nutty, faintly peppery flavor. A crop that stops and restarts gives narrow, tough, fiercely hot leaves that most people cannot eat.
The heat in the leaf comes from glucosinolates, and the plant makes more of them when it is stressed. Drought, heat, crowding and starvation all read as stress. This is the reason two beds sown from the same packet on the same day can taste completely different: one of them was allowed to check.
So the care regime is short. Water before it wilts, feed lightly and early, keep the roots cool, and harvest before the plant decides it has had enough.
If your arugula is always too hot to eat, look at watering before you look at variety. In eight cases out of ten the plant went short of water somewhere in its third or fourth week.
Watering: little, often, and never late
Arugula roots sit in the top six inches (15 cm) of soil and it has no reserve to draw on. A single afternoon of visible wilting is enough to coarsen the leaves permanently, and no amount of watering afterwards will soften them again.
Test with a finger rather than a schedule. Push it in to the second knuckle: if the soil is dry at that depth, water, and water enough that the moisture reaches down eight inches. A daily sprinkle that wets only the surface is worse than nothing, because it keeps the roots shallow.
Water at the base rather than over the top. Wet leaves overnight invite downy mildew, and in a dense stand the foliage stays wet until well after sunrise.
| Conditions | How often | How much | Watch for |
|---|---|---|---|
| Cool spring, open ground | Every three or four days | About half an inch (12 mm) | Soggy soil in a wet spring |
| Warm weather, open ground | Every one or two days | Half to three quarters of an inch | Midday wilting that does not recover by evening |
| Hot spell above 85F (29C) | Daily, in the early morning | Enough to wet 8 in (20 cm) deep | Leaves narrowing and standing upright |
| Containers | Daily, sometimes twice | Until it runs from the base | The pot drying to the point it pulls from the sides |
| Under cover in winter | Every seven to ten days | A light watering only | Gray mold on the lower leaves |
Feed lightly, and feed early
Arugula wants a modest, steady supply of nitrogen. Too little and the leaves go small, pale and hot. Too much and you get soft floppy growth that aphids find irresistible and that collapses in the first hot week.
A bed with compost worked in before sowing usually needs nothing else for a single four-week crop. Once you start cutting repeatedly, each cut removes leaf that the plant has to rebuild, and that is when a liquid feed earns its place.
Stop feeding once the plant looks like it is thinking about bolting. Nitrogen at that point produces a taller flower stem, not more leaf.
| Stage | What to give | Why |
|---|---|---|
| Before sowing | One or two inches (3 to 5 cm) of compost forked in | Holds moisture and covers the whole first crop |
| First true leaves | Nothing | Feeding now makes soft growth and no more leaf |
| After the first cut | Balanced liquid feed at half the label strength | Replaces what the cut removed and speeds regrowth |
| After each later cut | The same, once a week at most | Regrowth slows with every cut and needs the support |
| Flower stem visible | Stop feeding | The plant is committed to seed and will not turn back |
Pale yellowing that starts on the oldest lower leaves and moves upward is nitrogen shortage. Yellowing between the veins of the young leaves at the top is not, and feeding will not fix it.
Keeping the roots cool
Air temperature is not what the plant responds to most strongly. Root zone temperature is. A bed at 70F (21C) at root level behaves quite differently from one at 85F (29C) even on the same afternoon, and lowering it buys you real extra weeks of harvest in summer.
Two things do most of the work: a mulch and some afternoon shade. Neither is complicated, and both cost less than the sowing you would otherwise lose.
- Mulch as soon as the plants are two inches tall Lay half an inch to an inch (12 to 25 mm) of fine compost, grass clippings or straw between the rows. Keep it clear of the stems themselves so the collars stay dry.
- Shade from the west, not from above The damaging heat is afternoon heat. A panel of thirty per cent shade cloth on the sunset side does more for the crop than a flat cover overhead and does not cut the light the plants need.
- Use taller neighbors deliberately A row sown on the shaded side of staked tomatoes or beans stays several degrees cooler through the afternoon and lasts noticeably longer before bolting.
- Water early in the day Watering at dawn cools the root zone before the heat arrives and lets the foliage dry by evening. Watering at dusk leaves the leaves wet all night for no cooling benefit.
Containers and windowsills
Arugula is one of the best crops for a pot because the whole cycle is short and the root system is shallow. Six inches (15 cm) of depth is genuinely enough, and a broad shallow pan gives you more crop than a deep narrow pot of the same volume.
The one thing that goes wrong in containers is drying. A pot of compost in full sun can swing thirty degrees between dawn and mid afternoon, and the plants read every swing as stress. Move the pot to somewhere that gets morning sun and afternoon shade once summer arrives, and check it every single day.
Container plants also exhaust their nutrients faster because every watering leaches some away. Start the weekly half-strength feed after the second week rather than waiting for the first cut.
What to write down
Arugula is grown in successions, which means you get five or six chances a year to learn something and no chance at all to remember it accurately. Three lines in a notebook per sowing is enough to make next year's crop better than this year's.
Record the date you sowed and the soil temperature at sowing, where in the garden the row was, the date of the first cut, and the date you first saw a flower stem. The interval between those last two dates is the number that matters, because it is the length of the harvest window you actually got. Note down how the leaves tasted as well, and whether the plant went short of water at any point, and the pattern behind the hot bitter crops becomes obvious within a single season.
Also mark which bed each sowing went into. Arugula is a brassica, and rotating it away from cabbages, radishes and mustards for three years is the cheapest control you have for both flea beetle and soilborne disease.