YOUR SIMPLE GROWING PLAN
One pot. Here’s the plan.
Before you start Plant a locally suitable onion variety in its planting season: usually spring for northern long-day onions, fall or winter for southern short-day onions.
What you need · pot, mix & supplies
- One draining pot, 16 inches wide and at least 12 inches deep
- 6 young bulb-onion transplants of one variety suited to your region
- Fresh potting mix, a watering can, and a plant label
The soil
Miracle-Gro Organic Potting Mix (US, SKU 78951430). Contains starter nutrients; follow the feeding instructions on your actual bag.
A sunny patio in your local onion planting season. Start with young onion transplants.
At least 12 inches deep, with clear drainage holes.
Two rows of three plants, 4 inches apart in every direction.
See the planting illustration
- 01
Match the onion to your city
At a nursery, ask for bulb-onion transplants for your city: long-day for the North, short-day for the far South, or intermediate-day for the middle band. Check the variety label rather than buying by color alone.
- 02
Set out six starts
Fill the pot with damp mix. Make two centered rows of three holes, 4 inches apart. Set each transplant about 1 inch deep with its roots covered and green leaves above the mix. Water gently.
- 03
Let the bulbs show
Keep weeds out and moisture steady. As bulbs swell above the surface, leave them exposed. Do not heap mix around their necks.
- 04
Wait for tops to fall naturally
Keep bulbs exposed as they grow, but do not pull soil away from their roots or bend the leaves over. When most healthy tops naturally flop and begin drying, stop watering and lift gently. Use damaged or flowering onions first; cure sound bulbs before storage.
Other ways to start
Plant small onion sets+
Use six firm sets smaller than a penny, from a variety suited to your area. Plant pointed end up with about 1 inch of mix covering each set, at the same 4-inch spacing. Larger sets are more likely to flower; transplants give you clearer variety choices.
Raise your own transplants+
Start fresh onion seed indoors about 8–10 weeks before your outdoor planting date. Sow ¼ inch deep in seed-starting mix, keep it moist, and provide bright light. Raise extras, then select six healthy seedlings and gradually acclimate them outdoors.
YOUR EVERYDAY ROUTINE
Water & fertilizer at a glance.
- Water when
- During growth, water when the top inch starts drying and drain. Stop when mature bulbs have healthy tops naturally falling; shelter from heavy rain. Empty the saucer or outer pot after draining.
- Fertilizer
- Espoma Garden-tone (US 3-4-4)
- Amount
- 2 level tablespoons for the entire 16-inch pot
- What that amount covers
- Dry granules at the label rate of 1½ teaspoons per 4 inches of diameter. This is the whole-pot amount for all six onions.
- How often to feed
- No sooner than monthly, during early leaf growth only.
- When to start or pause
- Skip at planting in enriched mix. Follow the bag’s starter-feed period, then top up during leaf growth. Stop regular feeding when bulbs begin swelling.
Scatter granules around the outer edge, away from plants, then water in.
Use level measures and the exact US formula shown. If your label differs, follow it; do not transfer this dose to another formula or combine feeding programs.
See the watering & feeding illustrations
US PRODUCT REFERENCE
Espoma Organic
Garden-tone
3-4-4Granular: measure onto growing mix
Check the official US product ↗Illustrated reference; check the manufacturer’s current packaging and US label.
Bulb harvest timing and expected size
Many bulb-onion varieties need roughly 85–120 days, with substantial differences between spring and fall plantings. At 4-inch spacing, aim for useful kitchen-size onions rather than giant show bulbs.
Planting windows for your onion type
Northern long-day onions usually start outdoors in early spring. In the far South, short-day varieties commonly start in fall or winter. Ask your local nursery for the planting window for the named variety. “Long-day” describes seasonal daylight, not a reason to put the pot in shade.
For regional planting windows, find your local Cooperative Extension office ↗.
Something looking off?
Which onion type should I buy for my state?+
Use long-day varieties in the northern US and short-day in the southern US (about 35°N as a rough line). Intermediate-day types suit some middle latitudes—check the packet.
Can I grow onions from sets in containers?+
Yes. Sets or sturdy transplants are the beginner path in this guide. Sow seed earlier only if you can grow strong starts before potting up.
Why are there greens but no bulbs?+
Wrong day-length variety, crowding, weak light, or inconsistent water can limit bulbing. Confirm type first before adding fertilizer.
Should I cut onion tops to make bigger bulbs?+
Leave healthy leaves on plants you want to bulb. Cutting tops does not create larger storage onions; pull whole plants if you want green onions.
How do I store homegrown onions?+
Cure undamaged bulbs with tops attached in a dry, airy place until necks and skins are dry, then trim and store cool and dry.
Can pets share the harvest?+
No. Onions are toxic to cats and dogs. Keep the crop and discarded trimmings out of their reach; contact a veterinarian if a pet eats them.
Choosing the right onion for your region
Choose an onion matched to regional day length
You do not need to calculate sunlight hours every day. Choose a variety marked for your growing region once, and put the pot in full sun. A winter hardiness zone alone does not tell you which onion day-length type to buy.
Distinguish bulb onions from other onion crops
This plan grows six Allium cepa plants for bulbs. The two centered rows of three, 4 inches apart, are our container adaptation of published block spacing for moderate-size bulbs. Bunching onions and walking onions need different harvest plans. Growing a full-size bulb from kitchen scraps is not promised here.
Help with your next step.
- Set up a pot that drains
Choose drainage holes and manage the saucer before you plant.
- Read the fertilizer already in your mix
Check the actual bag before adding a second fertilizer program.
- Compare four other edible starter pots
The chart covers spinach, basil, cherry tomato and blueberry. Use it to compare alternatives; their pot sizes and feeding recipes do not apply to this plant.
Sources, dates & detailed PDF
Editorial plans, not results from a Plant Care Steps growing trial. Compiled with AI assistance; they have not yet had an independent horticultural review. Editorial approach.
- University of Maryland: onion spacing, day length, and harvest ↗
- Iowa State: transplants, sets, seeds, and onion care ↗
- Illinois Extension: northern and southern onion types ↗
- Espoma: Garden-tone formula and container amounts ↗
- Manufacturer: starter feed in the named potting mix ↗
- Dixondale Farms: day-length choice and stopping fertilizer at bulbing ↗
- Minnesota Extension: onion maturity and stopping water ↗
- ASPCA: onion and pets ↗
- Manufacturer: US fertilizer formula and application directions ↗
Something needs updating? Suggest a correction
Published · Updated
Sources checked View sources ↗
Detailed PDF ↓Full reference edition with expanded explanations and illustrations. Its publication dates appear in the file.
