Gadenin日本語Get the appWater deeply once or twice a week, never a daily splash
Broccoli roots run down 18 inches (45 cm) or more, and it wants an inch to an inch and a half (25 to 40 mm) of water a week including rain. Deliver that in one or two long soaks rather than a daily sprinkle. A light watering only wets the top inch, which draws the roots up to the surface where they cook in the first hot week.
The critical stretch is the three weeks while the head is swelling. Broccoli that dries out at that point produces a loose head with gaps between the clusters, and the stem can go hollow and woody at the center. If you are going to be away, mulch and soak beforehand rather than hoping for rain.
- Check at a spade's depth Push a trowel in beside a plant and look 4 inches (10 cm) down. Damp there means wait; dry there means soak the base thoroughly.
- Water the soil, not the plant Put the water at the base. Water sitting in the crown overnight encourages rot in the developing head and spreads downy mildew spores across the leaves.
- Mulch once the soil is warm and wet Two inches (5 cm) of straw or compost after a good soak halves the watering and keeps the soil temperature steadier, which broccoli cares about more than most vegetables.
Broccoli forms its best heads when average temperatures sit between 60F and 70F (15C and 21C). Above 80F (27C) heads open early and taste bitter, so in a warm spell shade cloth over the row buys you real quality, not just comfort.
Top dress with nitrogen three to four weeks after planting
Whatever you dug in before planting carries the plant through establishment. The feed that matters comes about three to four weeks later, when the plant is putting out big leaves and building the frame that will support the head. Scatter a nitrogen rich fertilizer in a ring 6 inches (15 cm) out from the stem and hoe it in lightly.
Give a second dressing when you can first see the head, about the size of a coin in the center of the plant. Stop feeding after that. Nitrogen applied once the head is filling produces soft, sappy growth that aphids find first and that stores badly after cutting.
| Timing | Feed | What it does |
|---|---|---|
| At planting | Balanced granular, worked in | Gets roots established |
| Three to four weeks after planting | Nitrogen rich top dressing | Builds the leaf frame that feeds the head |
| When the head is coin sized | Half the previous dose | Sizes the head up evenly |
| Head filling out | Nothing | Late nitrogen brings aphids and soft heads |
| After cutting the main head | Light liquid feed every two weeks | Keeps side shoots coming |
The leaves tell you what the plant is short of
Broccoli leaves are large and easy to read. Uniform pale green across the whole plant, oldest leaves worst, is nitrogen running out and it is fixed with a top dressing and a watering. Purple tinges on the undersides of the leaves in cool weather are phosphorus locked up by cold soil, and that corrects itself as the ground warms.
Two symptoms are worth knowing because they are specific to brassicas. Leaf edges scorching and dying back while the center stays green is usually a boron shortage, which also produces a hollow, brown stained stem. Yellowing between the veins on the older leaves while the veins stay green is magnesium, common on light soils after heavy rain.
| Symptom | Likely cause | What to do |
|---|---|---|
| Whole plant pale, oldest leaves worst | Nitrogen shortage | Top dress and water it in |
| Purple undersides in cool weather | Cold soil locking up phosphorus | Wait. It passes as the soil warms |
| Scorched leaf edges, hollow brown stem | Boron shortage | Correct pH and add boron before the next crop |
| Yellow between green veins, older leaves | Magnesium shortage | Foliar feed with Epsom salts |
| Wilting at dawn, no obvious pest | Root damage or clubroot | Lift one plant and inspect the roots |
Earth up and stake tall plants
By the time a broccoli plant is two feet (60 cm) tall with a head on top it is top heavy, and in an exposed spot it will lean and then loosen its own roots. Draw soil up around the base of the stem to a depth of 3 to 4 inches (8 to 10 cm) when you do the second feed. The buried stem puts out extra roots and the plant stops rocking.
On a windy site, or with sprouting types that stand for months, add a cane. Push it in 6 inches (15 cm) from the stem so you do not spear the rootball, and tie loosely in a figure of eight so the tie does not cut in as the stem thickens.
- Draw soil up at the second feed Hoe the top dressing in and pull the loose soil into a mound against the stem at the same time. One job, two purposes.
- Cane anything over two feet in the open Set the cane away from the rootball and tie loosely. Retie higher up as the plant grows rather than adding a tighter tie.
- Remove yellow lower leaves Snap off leaves that have gone yellow at the base. They shelter slugs and gray mold and the plant has already withdrawn what it needed from them.
Keep a note of the feed dates and the weather
Broccoli responds so directly to nitrogen timing and to temperature during head formation that a season's notes are worth more than any general rule. Record the date of each top dressing, the date you first saw the head, and roughly what the weather did in the fortnight in between.
After one season you will be able to see the pattern for your own garden: which planting hit the cool window and made a solid crown, and which one ran into a warm spell and opened early. That comparison is what lets you move the sowing date by the right amount rather than guessing.