How to Manage Pests

Pests in Gardens and Landscapes

Cultural Tips for Growing Onions and Garlic

In This Guide

Site selection

Plant your garden in a convenient location, where you can check it frequently. Choose an area near an abundant supply of water so you can water as needed easily. Vegetables do best if they receive full sunlight (at least 4 to 6 hours a day). Plant them in a well-exposed area in the garden, where they are not shaded by trees, fences, or walls. Try to plant away from areas that will be watered by lawn sprinklers.

Whenever possible, select a location that is not heavily infested with weeds, especially weeds such as field bindweed, nutsedge, and Bermudagrass that can be hard to control with hand weeding. Also avoid areas that have had previous disease problems.

Try to plant on level ground. Level ground is easier to work on than sloping ground. Vegetables will do well on a wide range of soils; they do best in well-drained soils. If your soil forms a clump when squeezed, then it is too wet; if the soil crumbles easily, it is a good soil to use. Damp soil surfaces encourage snails, slugs, sowbugs, and root diseases; fruit decay and leaf spot diseases may also increase. Soil amendments can make clay and sandy soils easier to work with, and correct soil preparation can improve poor soil.

Adding organic matter (compost, peat moss, manure, sawdust, ground bark) makes clay and sandy soils easier to work with. The soil should be kept at a pH level of 6.0 to 6.5. Lime or gypsum can be added to soils low in calcium.

Soil recommendation

Avoid areas with rocks, high salinity, or excessively dense clay.

Soil improvement

Any type of soil can be improved with soil amendments. Heavy clay or sandy soils can be improved by adding organic material such as compost, manure, or leaf mold. Texture is an important consideration when choosing an amendment. An amendment that is granular and fine grained is important for container mixes. For gardens, a more coarse-grained amendment can improve drainage and aeration. Work amendments into soil by rototilling, raking, or double-digging.

Soil preparation

The preparation of your soil is just as important as adding fertilizer and soil amendments. Before working the soil, make sure it is moist but not thoroughly wet.

  1. Use a shovel, rototiller, metal bow rake, or all of them together to loosen the top 1 to 2 inches of soil. Rake the area to remove weeds and old crop debris. Be sure to dig out roots.
  2. Irrigate the plot deeply to encourage the germination of weed seeds.
  3. In a week or two, after a substantial number of weeds have germinated, work the area again to kill the weed seedlings. Be sure to break up the clods in the soil, as seeds planted in cloddy soil will germinate poorly and won't live long because the soil dries too quickly.
  4. Form soil into beds if desired, and plant while soil is still wet.

Time to plant

Temperature plays an important role in the development of onion bulbs. However, in order to initiate bulb formation, day length is more critical. Each onion variety has a critical day length for inducement of bulbing regardless of temperature or plant size. Short-day onions require day lengths of 12 to 14 hours. Long-day varieties require 14 to 16 hours of day length. Growing onions at less than critical day length results in formation of new leaves but no bulbing. When short-day onions are grown under long-day conditions, bulbing develops while the plants are very small and results in small bulbs (great for cocktail onions).

Garlic is generally best planted in the fall for largest size bulbs at harvest. Later planting is acceptable but bulb size may be smaller. Bulb formation begins in response to lengthening days. In cold-winter areas, mulches around the plants will protect them from severe cold.

Planting Dates for Onions and Garlic in California*
North and North Coast
Monterey County north
October – December (garlic)
April – July (green onions)
January – March (bulb onions)
South Coast
San Luis Obispo County south
October – December (garlic)
All year (green onions)
February – March (bulb onions)
Interior Valleys
Sacramento, San Joaquin valleys
October – December (garlic)
August – December (green onions)
November – March (bulb onions)
Desert Valleys
Imperial and Coachella valleys
September – November (garlic)
September – January (green onions)
October – November (bulb onions)
*Planting dates are only approximate as the climate may vary greatly within the regions denoted. Contact your local UC Master Gardener program and experiment on your own to find more precise dates.

Planting Onions and Garlic

Onions can be grown from seed, sets, or transplants. Onions produce better from seed or transplants rather than from onion sets. Much of the energy in onion sets seems to go into producing seed stock instead of bulbs. Onion sets (small bulbs), unless properly stored, will tend to bolt rather than set a large bulb. To sow directly into the garden, plant seed about 0.25 inch deep and maintain good soil moisture. Plant more seeds than necessary and then thin plants, using the small plants as scallions or as transplants for other areas. Save the strongest transplants to produce bulbs. Space transplants about 4 to 5 inches apart and plant to cover the base of the bulb with just enough soil to anchor it in place. In a suitable climate, green onions may be planted more than once a year for a continuous harvest

Most garlic is grown from the separated cloves of the garlic plant rather than from seed. Plant the bulblets directly in the garden. Do not remove the papery covering on the bulblet. Do not break apart the mother bulb until the plant is ready to plant. Plant 2 inches deep and space 4 inches apart in the row, with 12 inches between the rows. The larger the bulblet, the larger the bulb of garlic at harvest.


Most vegetables require fertilizer for growth. Organic materials, such as manures and compost, and inorganic materials, such as chemicals, can be used to fertilize plants. Using both types of materials usually provides the best growth. Manures and compost can be used to increase soil fertility. They are usually applied at 1 pound per 4 or 5 square feet. These materials should be worked into the soil several weeks before planting in order to allow it to decompose. Manure that contains straw, sawdust, or similar materials should be applied with a commercial nitrogen fertilizer. Generally, if the soil has been properly amended with compost or manures or other organic materials, the only nutrient needed is nitrogen, if anything. Some commercial nitrogen fertilizers available are urea, ammonium sulfate, calcium nitrate, and ammonium nitrate. Apply these fertilizers at rates of 0.5 to 1 pound of nitrogen per 100 feet of row.

If manure and other organic material has not been used, apply fertilizer that contains both nitrogen and phosphorus before planting. All commercial fertilizers are labeled by the percentages of N-P-K; nitrogen (N), phosphorus (P), and potassium (K). Some common mixed fertilizers are 5-10-5, 5-10-10, 8-16-16, and 12-12-12. Apply these fertilizers at rates of 1 - 2 pounds per 100 feet of row. After plants are 3 to 4 inches tall, sidedress nitrogen in narrow bands or furrows and water thoroughly after application, or apply through the drip system. Consider light but frequent applications of nitrogen fertilizer every 3 to 4 weeks. Avoid letting the fertilizer come into contact with the plant stems to avoid burning.

Application tips

Inorganic fertilizers can be sidedressed. Manures are more difficult to use as a side dressing and must be tilled into the soil.

Banding: Make a small groove 1 or 2 inches deep on both shoulders of the bed, 4 to 6 inches from the plant row and band in the fertilizer. Replace the soil and irrigate.

Broadcasting: Fertilizers can be scattered along the bed shoulders. Work into the soil soon after. This is less efficient than the banding method but will be more practical when the plants are so large that the bed shoulders are inaccessible for banding.

Where sprinklers are used, fertilizer may be scattered on the soil surface between rows before irrigating. Where drip or trickle tubes are used, apply fertilizer on the soil surface near the drip tube.

Watering Onions and Garlic

Onions have a fairly high water requirement. The soil needs to be kept evenly moist throughout the growing season. Water stress during the development period will affect flavor. Infrequently applied or insufficient water increases the pungency. As the onions approach maturity and the tops begin to fall over, water should be withheld to stop root growth and allow the outer scales of the bulb to become dry.

In many areas, winter rains supply adequate moisture for garlic during the early part of the growing season. If there is inadequate rainfall, irrigation may be necessary. For best yields, never drought-stress garlic before the first signs of maturity. Garlic is shallow rooted, so wet to 2 feet with drip irrigation when you do irrigate. When the crop approaches maturity (when the tops begin to break or become dry), stop irrigation to allow drying.

Harvesting and Storing Onions and Garlic

Onions and garlic are ready to harvest when the tops bend to the ground, become dry, or in the case of garlic, the cloves begin to separate in the bulb. Garlic and onions take about 120 days or more to mature. Both garlic and onions need to cure before being stored. They may be dug and left in the garden to dry. Protect the bulbs from sunburn by covering them with the tops of other plants. Onions can also be placed in burlap bags and left outside to dry naturally. Garlic, in small quantities, may be braided and hung to cure that way.

Yellow onions.

Yellow onions.

Seed bed preparation.

Seed bed preparation.

Amending soil to prepare for planting.

Amending soil to prepare for planting.

Bag of fertilizer.

Bag of fertilizer.

Irrigation shut off valve.

Irrigation shut off valve.

Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2020 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See our Home page, or in the U.S., contact your local Cooperative Extension office for assistance.

Agriculture and Natural Resources, University of California

Accessibility   Contact webmaster.