Onion Care At A Glance
- Short-Day onions are best for southerly climates. They need 10-12 hours of sunlight to develop bulbs. They are generally sweeter and less pungent in taste due to higher sugar content with less sulfur, which means they don't store as long as others.
- Long-Day onions perform best in northern regions. They need 14-16 hours of sunlight to produce bulbs. LD types have higher sulfur with less sugar making them more pungent and have longer storage capacity.
- Day-Neutral or Intermediate onions are hybrids that can bulb at a range of 12-14 hr. day length so they can be grown equally well in northern or southern locations. However, other factors for good growth must also be met to yield a good crop.
Onion Planting Instructions
Onions are a cool season crop and should be planted early enough to have good growth prior to the appropriate day length when top growth stops, and bulb formation begins. However, planting too early can lead to bolting. Too much early cold can fool onions into thinking it is time to flower when temperatures suddenly rise in early summer.
- Onions prefer a full sun location with deep, organically rich, well-draining soil.
- Onions are considered heavy feeders (see Onion Fertilizing Garden Guide)
- To harvest larger bulbs, space starts 4-6 inches apart.
- If smaller bulbs are desired or green onions are, then space bulbs 2-3 inches apart.
- Rows should be 12 to 15 inches apart.
- Plant transplants 1 to 1.5 inches deep.
Watering
Onions, like other vegetable plants, perform best with consistent and ample water during the growing season.
- Water onions using the 1-2 inches per week rule, which equates to about 2.5-5 gallons every 2-3 days.
NOTE: Well-draining soil is important to help prevent root rot and other potential fungal issues.
- Always check soil moisture prior to watering.
- Apply ample amounts of clean mulch material around plants to help suppress weeds and retain valuable soil moisture between waterings.
Onion Care - Maintenance After Establishment
Small-Sized Onion Bulbs at Harvest
Causes & Solutions:
- Improper Day-length. Bulb formation is dependent on day length rules (see descriptions above), choose the right variety for your location. If the variety is appropriate for your area, but bulbs are still small then consider the 3 other main factors.
- Planting too late. Onions are a cool season crop and should be planted early enough to have good growth prior to the appropriate day length when top growth stops, and bulb formation begins.
- Improper fertilizing. Onions are heavy feeders, but improper feeding with the wrong fertilizer formula or at the wrong time can be detrimental. Review specific fertilizing rules in Onion Fertilizing Garden Guide.
- Time to harvest. Know what to expect from different planting forms. Time to harvest is variable depending on what form you start with. Whether that is from seeds, transplants, or sets.
- Soil is too dry. Small bulbs can result from underwatering. Follow the proper watering guidelines above.
NOTE: Double bulb formation also results commonly soil that is too dry.
- Bulb spacing. For larger bulbs, space sets 4-6 inches apart. If smaller bulbs are desired or green onions, then space sets or transplants about 2-3 inches apart. Rows should be 12 to 15 inches apart. Plant sets or transplants 1 to 1.5 inches deep.
NOTE: These issues may happen simultaneously making diagnosis after the fact difficult. Avoid small bulbs at harvest by ensuring all these factors are done properly initially.
Sharp or Pungent Tasting Onions
Firstly, the general flavor of onion is determined by variety and type.
- Long-day types have a strong more pungent flavor. LD types contain higher sulfur content making them better for longer storage.
- Short-day types are described as comparatively sweeter with higher sugar content and less sulfur, which makes for limited storage compared to LD types.
- Day-neutral types can have flavors ranging between both of these.(/li>
Other causes: A stronger, more pungent onion flavor than normal is usually due to heat and or drought stress.
- Keep onions consistently watered.
- Mulch well to help moderate soil temperatures (onion roots are shallow and wide)
- Plant onions in early spring to ensure they get the start they need.
Leaf Diseases
Several forms of leaf diseases can affect onions.
- Botrytis, downy mildew, and white rot are the most common fungal diseases.
- Utilize multi-step prevention techniques.
- Ensuring proper soil drainage and watering are important.
- Rotate onion plantings year to year. (Plant onions in place of beans or other legumes)
- Employ proper sanitation methods such as controlling competitive weed growth that limits air circulation and promotes unwanted host pests.
- By the time onion foliage is displaying symptoms it is too late for fungicide applications but late-season applications of broad-spectrum type like Fung-onil® by Bonide® can help prevent issues following seasons.
