How To Grow Bulbs

This page summarizes our members’ advice on growing bulbs. There’s a lot of information, but here are the four most important issues to focus on:

  1. Know when your bulbs want to be watered. Some grow in the winter and need to be kept dry in summer; others grow in summer and need to be dry in the winter. If you water a bulb at the wrong time of the year, it may rot.
  2. Know how much cold they can take. Some bulbs native to cold climates expect a lot of cold in winter, and may not bloom or even grow if your weather is too warm. Others are native to mild areas and will tolerate little or no frost. In this wiki you can find notes on the basic preferences of the bulbs you're growing.
  3. When in doubt, use pots. Many bulbs will grow in the ground, but when you’re learning, it’s often easier to grow them in pots because you can control their conditions more closely, and protect them from pests.
  4. Make sure you have good drainage. Whether you grow bulbs in the ground or in pots, using well-drained soil is almost always essential.

Master those four things and you’ll probably be successful. If you want more details, here are the topics we cover below:

Introduction
Climate issues
Growing in containers vs. in the ground
Soil
Watering
Protection from frost
Labels
More information

Introduction

Buy them. Stick them in the ground. Enjoy the flowers.

If you buy flower bulbs at the local garden center, that's about the most information you'll get. And it works well if you're growing a hybrid Gladiolus and don't care if it comes up again next year.

But growing species bulbs, the things we discuss here, is a different story. Some of them are fussy about soil and watering, and many of them aren't even available as bulbs. You'll need to grow them from seeds, and they'll take a couple of years to reach blooming size -- so making sure they survive several years is pretty important.

Why go to all that bother? If you're a gardener it's a fun challenge, and as a reward you'll get flowers that look like nothing you can find in the local nursery. Your gardening friends will be jealous, and your spouse...well, if you're reading this your spouse probably already thinks you're nuts, so this won't change anything.

Besides, once you get the hang of it, growing these things is actually pretty easy.

Climate issues

The first step in growing a species bulb is to compare your climate to the native climate of the bulb. In general, the more similar your climate is to the home of the bulb, the easier it will be to grow. If your climate is different from the bulb's home, you will need to artificially simulate the climate it expects.

Timing of rainfall. Many species bulbs are native to mediterranean climate parts of the world, which have rainfall in winter and are more or less dry in summer. Putting water on a mediterranean climate bulb in summer will usually cause it to rot. So if your climate has summer rain, you'll need to protect your mediterranean-climate bulbs from it.

Also, keep in mind that not all "mediterranean" climates are created equal. They vary tremendously in temperature ranges and in the duration and intensity of the summer drought. For details, check out our mediterranean maps.

Wikipedia discussion and map of the world's Mediterranean climate areas

On the other hand, some bulbs (Tigridia, Habranthus, etc) come from summer-rain areas like the eastern part of South Africa and much of Mexico. If grown in a Mediterranean-climate area, they often need to be protected from rain in the winter and must be watered in summer.

Cold. Some bulbs are adapted to living under the snow in winter. They won't grow properly unless they get a good cold dormancy, and people growing them in mild climate areas have to refrigerate them in order to get them to grow. For example, many Tulipa species and some Narcissus need a cold winter in order to bloom properly. Bulb dormancy discussion.

Drainage. Almost all bulbs need good drainage. With a few exceptions, if they're grown in heavy soil they are much more likely to rot.

Should I grow in containers or in the ground?

Because of all these variables, many bulb enthusiasts grow their bulbs in containers. This allows them to ensure great drainage for the bulbs, protects them from burrowing pests like gophers, and because the pots can be moved or covered, they can be shielded from untimely rain. Although containers are probably the most reliable way to grow species bulbs, they also involve some more effort. Container bulbs must be repotted every few years, and even if your climate has rain at the right time, you have to give them supplemental water in the rainy season because pots dry out so much faster than the ground does.

Some bulb growers use raised beds instead of containers. Raised beds require less redigging and watering, but still have great drainage and are somewhat protected from garden pests. You do have to build the beds (often out of pressure-treated lumber), which can be a fair amount of work at the start. A disadvantage of raised beds is that some bulbs migrate, and after a few years it can be hard to keep track of which ones are which. Also, some aggressive bulb species can take over a raised bed and crowd out the other bulbs.

A compromise used by some PBS members is the "plunge bed." Bulbs are grown in pots, to keep them from spreading out of control, but the pots are surrounded by sand or some other neutral medium. This keeps the pots cooler, and lets the bulbs send out roots beyond the pot. Some members have reported excellent results with this approach.

Growing bulbs in ground requires the least effort, but needs the best match between your climate and the home climate of the bulb. Sometimes providing great drainage (by planting in a mound) can help you grow a bulb in the ground outside its usual climate area. Bulbs in ground are also the most exposed to local soil diseases, insects, and furry creatures that may eat them.

If you're just getting started, probably the best thing to do is try a few in pots and take it from there.

How big should the pot be? This is another question without a single perfect answer. Some bulbs like to dive deep, and need deeper pots. Other stay close to the surface. Some (Nerines, for example) reportedly flower better when a bit crowded. A few (such as Moraea vespertina) generally refuse to bloom unless they are grown in the ground.

A good starting point is an 8-inch (20- cm) pot with about five or six bulbs in it. Use fewer bulbs if they're very large (one large tulip is enough for a single pot). But most species bulbs are small and don't mind a bit of crowding.

Your choice of plastic or clay pots depends on your climate. In a wet climate like the UK, clay pots are helpful because they dry out faster and help to prevent rot. In much of California, clay pots dry out too fast, and plastic is a better choice.

What soil should I use?

This is a religious debate among bulb enthusiasts. Everyone has their own recipe for the ideal bulb potting mix, and in fact there probably is no perfect choice. But everyone agrees that it needs a good combination of drainage and moisture retention, with a variety of particle sizes to help air penetrate the soil. Having a huge amount of organic matter in the soil isn't a great idea because it can encourage disease. That means your typical packaged potting mix from the garden center may not be a good choice, unless you add a lot of sand or pumice to it. Cactus mix can sometimes work well (it's better-drained).

In 2007, Paul Cumbleton of RHS Wisley Garden in the UK wrote an excellent essay about potting mixes for the PBS discussion list. Although he was focused on alpine plants, his advice also applies to bulbs. We encourage you to read it here.

The University of California campuses have done extensive research on soil mixes for use in containers, in support of California's agriculture industry. These mixes are designed for use in growing ornamental plants and fruit trees in immense quantities in commercial greenhouses, so they may not be perfect for growing bulbs at home. But they are the product of a lot of controlled experimentation, so they'll at least give you a starting point to think about.

The original UC Mix was 50% peat and 50% sand, supplemented with fertilizer. This mix is still used by some bulb growers today, and it often produces good results. The UC has moved on to more advanced formulations, but they often retain the 50-50 mix of inert drainage material and organic material.

UC Riverside soil mixes combine two parts of plaster sand (similar in texture to beach sand, but well washed), one part of ground bark, and one part of peat. This is supplemented with various nutrients. For details, click here.

UC Davis has created several mixes. The most common is one part peat moss, one part "uniform coarse sand with no silt," one part white pumice, and one part redwood compost (large-grained bits of bark and wood left over from the processing of redwood lumber). This is supplemented with three pounds (1.4 kg) each of oyster shell, dolomite, and single super phosphate per cubic yard (.75 cubic meters) of mix. For more details, click here.

(Redwood compost is widely used in gardening in California because redwood breaks down very, very slowly. If you can't get redwood compost, try to substitute a compost that decomposes very slowly. Home-made garden compost does not qualify.)

The UC Davis mix is designed to be used with a continuous fertilization system that delivers nutrients with every watering. Many data sources suggest that this sort of constant fertilization is best for container plants, but it's not easy to do for many home gardeners. If you can't water with fertilizer, supplement your soil mix with a commercial fertilizer that has micronutrients. Osmocote and other encapsulated fertilizers are not recommended by many PBS members, due to reports that they can release all their nutrients at once in hot weather.

Bonsai enthusiast groups can be a great resource for soil ideas. They grow plants long-term in pots, and are constantly experimenting with soil mixes and fertilizers.

Growing Medium describes some of the ingredients that many of us use in our soil mixes.

How often should I water?

When the bulbs are dormant, most of them should not be watered at all. Keep the pots in a cool, dry place. Under shade cloth can work nicely if you're in a hot climate. (On the other hand, if you live in a damp cool climate, you may need to leave the pots "baking" in the sun just to get them to dry out.) For winter-growing bulbs, start watering in the fall after temperatures have started to drop. In the Northern Hemisphere, that's usually around October.

There are some important exceptions to the "no water in summer" rule. Many South African Amaryllids (Nerine, Brunsvigia, etc) have fleshy roots that do not like to completely dry out in summer. If you live in a dry-summer climate like California, you need to take this into account. In the ground they will probably be fine if left alone (although even there, some seem to benefit from an occasional drink). In pots, they may grow better if they get a bit of water every few weeks in summer. The same thing applies to many Alstroemeria.

Once the growing season has started, let the top of the soil dry out a bit between waterings. If moss is growing on the soil, it may be a bit too wet. But do not let the soil ever get completely dry while the bulb is in growth. As a general rule, a heavy soaking once a week is usually about right. Desert bulbs will need less water, and bulbs that like a lot of water (Spiloxene, for example) may want a bit more. (For a water-loving bulb, it is sometimes useful to stand the pot in a deep saucer, so there is always some water available at the bottom of the pot.) Experiment.

Do I have to protect them from frost?

That varies from species to species. Most mediterranean-climate bulbs can tolerate at least a few degrees of frost at night, and some that grow in extreme climates are very hardy. But a prolonged freeze, one that makes the top of the soil stiff for a day or longer, can be deadly to many winter-growing bulbs from the mediterranean regions. If you get extended freezes every winter, you may need to protect tender bulbs in a greenhouse or cold frame. If you get occasional hard frosts, a fabric row cover may be enough to protect your plants.

What about labels?

Believe it or not, this is a complicated subject. When you start growing bulbs in pots, you'll think that any old label will do. But after a few years you may find that the labels will break, or fade, or just plain disappear. If that happens and you have a lot of pots, you may find it very difficult to identify which bulbs are which.

The PBS list had an extensive discussion on this subject in 2009. You can find the start of the thread here. Some highlights...

Fading labels


Label materials and loss of labels


For more information

The links below give additional information on specific bulb-growing topics:

Other wiki pages
How to grow bulbs from seed
How to grow Calochortus

Elsewhere
Notes on growing California native bulbs
How to grow South African bulbs
Ian Young's Bulb Log. This is the weekly online diary of a very accomplished bulb grower, hosted by the Scottish Rock Garden Club.
Vegetative propagation (how to cut apart one bulb and make it into many)
Fertilizers (PBS discussion thread)

Raised beds
Using raised beds in a wet-summer climate
Raised beds in California

Bulbs for various climates
Bulbs for continental climates (PBS discussion)
Bulbs for the Pacific Northwest Gardens (PBS discussion
Bulbs for Mediterranean gardens (PBS discussion)
Bulbs for Continental climates, Upper Midwest (PBS discussion)
Bulbs for Texas (PBS discussion)

Special situations
Growing tender bulbs in cold climates (PBS discussion thread)
Coping with cold; Bulbs for frozen soil (PBS discussion)
Bulbs with surprising hardiness (PBS discussion)

The links below are papers from two men who are/were passionate about growing bulbs:
Creating the Right Environment and Conditions for Growing Bulbous Plants, a speech by Gordon Summerfield at the 2003 IBSA Bulb and Seed Symposium.
A Non-Concise Guide to the Cultivation of Bulbs written by Stan Farwig

"What works for me"

This wiki has contributors from all over the world, in almost every climate and continent. Our gardens have different patterns of rainfall, soils, insect pests, and temperature. So a bulb-growing technique that works perfectly for one person might be a disaster for someone else.

The section below lists cultivation tips from some of our contributors. When reading them, keep in mind the author's climate.

Michael Mace, San Jose, CA (Mediterranean climate, minimum winter temp 20 °F / -7 °C)

I grow most of my bulbs in 8-inch pots in a mix of 50% peat, 25% sand, and 25% perlite. I used to grow in 50-50 sand and peat, but got tired of the weight of the pots. To each pot I add a small handful (maybe two tablespoons/30 cc) of a complete fertilizer (6-10-10 with micronutrients). I used to use a special bulb fertilizer mix made by Lily Miller, but they switched to an organic formula, and I find that organic fertilizers encourage bulbs in pots to rot (I think it's all that chicken manure).

I stick a square piece of 1-inch chicken wire under the top inch of soil in most of my pots. The purpose of the wire is to keep out rodents, which ate a lot of my bulbs until I figured out how to keep them out. Some bulbs make thick stems, and you can't use the chicken wire on them (Lachenalias are an example).

The wire needs to be just under the soil, not above it, or it'll prevent you from pulling out weeds.

My bulbs grow and bloom best when repotted at least once every three years, but I don't always hit that schedule. Many of them will live a long time without repotting, but the flowering drops off dramatically.

The bulb pots are on terraces on a south-facing hillside. I keep the pots on raised wooden pallets, which makes it harder for snails to climb onto the pots. I also put out snail bait on a regular basis throughout the growing season.

The pots are watered by an automatic drip irrigation system, with one 1-gph dripper per pot. The water runs for an hour every five days. I have to keep an eye on the drippers to make sure they don't clog, but even so this is a much easier system than watering 500 pots by hand every week.


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Page last modified on September 25, 2013, at 11:41 PM