Growing Citrus Trees from Seed – Fruit to Seedling

This article shows the process of growing citrus trees from seed from harvesting the fruit and extracting the seeds all the way to germination.

Growing Citrus Trees from Seed.
Growing Citrus Trees from Seed.

I have long wanted to write this article due to countless publications incorrectly teaching that to grow an orange tree or lemon tree from seed, a seed from the desired variety should be germinated. The typical method used by citrus nurseries to grow a citrus tree is to first germinate a citrus rootstock seed and then graft a bud of the desired variety to the resulting seedling. I thank TreeSource Citrus Nursery in California’s central valley for allowing me to see their process and share it with you in this article.

Growing Citrus Trees from Seed – from Harvesting Fruit to Germination – YouTube Video

In addition to this article, I have made a YouTube video showing growing citrus trees from seed.

Citrus nurseries in California start their rootstock seedlings with seeds from the fruit of mature rootstock trees that are registered with the California Department of Food and Agriculture. These are special trees in that they are periodically tested to ensure that they are free of pathogens that cause citrus diseases. The pathogen that causes HLB, the deadliest known citrus disease, is not transmitted via seeds. Some other citrus pathogens are seed transmitted, however, so testing is important.

a citrus rootstock tree
A citrus rootstock tree.

The seeds come from special varieties of citrus and citrus hybrids called rootstocks. There are many rootstock varieties. The typical rootstock fruit tastes terrible, but that is not important because the fruit to be eaten comes from the scion, the fruit-producing citrus variety that is grafted to the rootstock. The right rootstock can give a citrus tree resistance to disease, poor soils, or frost. Also, certain rootstocks can make the fruit of the grafted variety more flavorful than others.

Harvesting the Rootstock Fruit

The rootstock fruit is harvested by grabbing tree branches with a hook and shaking them.

Fruit is then raked up and put in a crate. The fruit is harvested when it is ripe and ready for the seeds to be extracted.

citrus rootstock fruit in crate
Citrus rootstock fruit in crate.

Extracting Rootstock Seeds from the Fruit

The fruit is run through an extractor machine to separate the seeds from the fruit.

citrus seed extraction machine
Citrus seed extraction machine.

Seeds exit the machine via one chute. The rest of the fruit exits the machine via another chute.

Citrus seeds exiting the extractor.
Citrus seeds exiting the extractor.

The fruit is sent through the extractor multiple times to extract more seeds.

citrus rootstock fruit going through the extractor again
Citrus rootstock fruit going through the extractor again.

Rinsing the Citrus Rootstock Seeds

The seeds from the extractor are rinsed with water. During this process, floating seeds are discarded as they will not germinate. Only the sinkers are kept.

rinsing the citrus rootstock seeds
Rinsing the citrus rootstock seeds.

The seeds at this point are slimy and acidic.

citrus rootstock seeds are slimy and acidic
The citrus rootstock seeds are slimy and acidic.

Eliminating the Slime

To eliminate the slime and lower the acidity, the seeds are stirred into a mixture of water and lime and then rinsed.

eliminating the slime from citrus rootstock seeds
Eliminating the slime.

Heat Treatment and Fungicide Application

Next the seeds go through a heat treatment to eliminate some pathogens. The seeds are soaked for ten minutes in water mixed to achieve a temperature of 52 degrees Celsius. After the heat treatment the seeds are treated with a fungicide to keep them mold-free.

heat treating the citrus seeds and applying fungicide
Heat treating and fungicide application.

Drying the Citrus Rootstock Seeds

Next the seeds are spread out to dry in the mild Autumn sunshine typical of California’s central valley. When the seeds are dry, they are collected and taken to the seed sorter.

drying the citrus roostock seeds in the sun
Drying citrus rootstock seeds.
mild autumn sunshine in California's central valley
Mild autumn sunshine in California's central valley.

Sorting and Storing the Rootstock Seeds

The seeds are sorted into multiple sizes and then packaged.

sorting the citrus rootstock seeds
Sorting the citrus rootstock seeds.

Seeds that are not germinated right away are placed in cold storage and used throughout the year.

citrus rootstock seeds in cold storage
Citrus rootstock seeds in cold storage.

When it is time to plant the seeds, the seeds are peeled. Peeled citrus seeds germinate much faster than unpeeled citrus seeds and the seedlings from peeled seeds have straighter, healthier roots.

Peeling the Rootstock Seeds

First the seeds are chemically treated to soften the seed coat. Then vermiculite is used to rub the seed coats off of the seeds.

peeling the citrus rootstock seeds
Peeling the citrus rootstock seeds.

A fan is used to separate the seeds from the seed coats, which are blown away.

separating the seeds from the seed coats
Separating the seeds from the seed coats.

Preparing the Pots

To get ready for the seeds, pots are filled with a growth medium that is then watered.

filling and watering
Filling pots with growth medium and watering.

Protecting Citrus Rootstock Seedlings from Insect Pests

To protect them from insects that spread citrus diseases, the seedlings are grown inside an insect proof greenhouse.

insect proof greenhouse
Insect proof greenhouse.

When employees enter or leave the greenhouse, insects are excluded by a double-doored vestibule in which only one door may be open at a time.

Exterior door of the entry vestibule.
Exterior door of the entry vestibule.

A fan is triggered to blow insects out of the structure whenever the outside door is opened.

Interior door of the entry vestibule and fans that are triggered by opening of the exterior door.
Interior door of the entry vestibule and fans that are triggered by opening of the exterior door.

Planting the Citrus Rootstock Seeds

Even in cold storage the viability of citrus seeds declines with time. Later in the season when the viability of the seeds is lower, seeds are planted two per pot.

planting citrus roostock seeds
Planting citrus roostock seeds.

Having been peeled, the rootstock seeds begin to germinate quickly.

citrus rootstock seeds germinating
Citrus rootstock seeds germinating.

Sorting the Citrus Rootstock Seedlings

Unlike most nursery plants, individual citrus rootstock seedlings grow at different rates and must be sorted two times in the growing cycle of four to six months.

sorting the citrus roostock seedlings
Sorting the citrus rootstock seedlings.

Bud Grafting the Rootstock Seedlings

When the seedlings are of sufficient size, they are budded with the desired scion variety. Click here to read my article on how the citrus rootstock seedlings are budded.

Grafting Citrus Trees by Chip Budding in a California Nursery.
Grafting Citrus Trees by Chip Budding in a California Nursery.

Buying Citrus Trees from Reputable Nurseries is Critical

Huanglongbing is the deadliest known citrus disease. It spreads much more readily than other citrus diseases via Asian citrus psyllids and by movement of citrus budwood and citrus trees. When buying a citrus tree, you can avoid introducing huanglongbing and other citrus diseases into your yard by buying your tree from a reputable nursery.

Acknowledgement

I thank TreeSource Citrus Nursery for allowing me to view their process of growing citrus rootstock seedlings from seed and share it with you.

Resources for Californians

Please visit CaliforniaCitrusThreat.org for more information on how to stop the spread of deadly citrus disease.

California Law Regarding Citrus Propagation

In California, the collection of any citrus propagative materials, including budwood and seeds, from non-registered sources is illegal. Any citrus trees grown or grafted in California must come from source trees registered with either:

Funding

This article was funded by a grant from California’s Citrus Research Board.

Similar Posts

Leave a Reply

Your email address will not be published.