Grapefruits (_Citrus x paradisi_) stand out among other citrus varieties with their large size and mouth-puckering fruit, which contains anywhere from none to more than 60 seeds. Fresh grapefruit seeds sprout readily and can be used to grow a tree, although seed-grown trees lack some of the advantages of grapefruit trees from a garden center.
Grapefruits fall into two categories: white-fleshed and red-fleshed. Common white-fleshed varieties include the 'Duncan' grapefruit (Citrus x paradisi 'Duncan'), which is a seedy variety with 30 to 50 seeds in each fruit. Red-fleshed varieties include 'Ruby' (Citrus x paradisi 'Ruby'), which is a common grapefruit at supermarkets. 'Ruby' is a seedless variety, which means it has six seeds or fewer per fruit.
All varieties of grapefruit grow in U.S. Department of Agriculture plant hardiness zones 9 through 11, although most cultivars will also grow in zone 8b once established.
Grapefruit trees are typically propagated with to increase their resilience and hasten fruiting. Seed-grown grapefruit trees often prove less reliable than their nursery-grown counterparts, and may include drawbacks such as:
- Delayed fruiting. Seed-grown grapefruit trees can take four to five years to flower or fruit. In extreme cases, flowering and fruiting can take up to 15 years.
- Shorter life span. Grapefruit seedlings are often short-lived. Disease, cold and drought kill seedling more easily than grafted trees.
- Strange fruit. Grapefruit seeds are polyembryonic which allows them to grow true to type. But mutations can create seedlings of varying quality. Plant more seeds than you plan to use so you can choose the strongest.
Grapefruit seeds do not require extensive preparation, although the seeds must be sown fresh. Have your pots prepared before you open the grapefruit up. Rinse the seeds in clean water after removing them from the fruit to get rid of the sugary residue, then pat them dry on a paper towel. Do not let the seeds dry out completely.
Seeds taken from ripe fruit perform best, so only collect seeds from grapefruits with a solid, pure gold skin with no hint of green at the ends.
Sowing and Germination
Grapefruit seeds can be started any time of year, although they perform best when started in spring as the days lengthen and the weather warms.
Wash a small plastic pot that has multiple drainage holes around the base. Size doesn't matter, although smaller, 2- to 3-inch pots warm up more easily. Dry the inside with a clean cloth.
Fill the pot to within a 1/2 inch of the top with sterile, soilless potting medium, or create your own by combining equal parts milled peat moss and half perlite or medium-grain sand. Saturate the mix with water and let the excess drain off for 15 minutes before sowing.
Sow three grapefruit seeds in the pot. Sow the seeds at equal distance from one another at a depth equal to twice their length. For example, a 1/8-inch-long grapefruit seed should be sown at a depth of 1/4 inch, while a 1/4-inch-long seed should be sown 1/2 inch deep.
Cover the seeds completely with soil to block out the light. Loosely drape a sheet of plastic wrap over the pot and move it to a warm spot where temperatures stay between 70 and 80 degrees Fahrenheit. A propagation mat works well, but the pot will stay just as warm on top of a refrigerator.
Lift the plastic wrap and water the grapefruit seeds whenever the soil feels dry on the surface. Add water slowly to avoid dislodging the seeds. Keep the soil moist in the top 1 inch or so. Put the plastic wrap back in place after watering.
Watch for the first grapefruit seedlings in two to three weeks. Remove the plastic after they emerge, and move the pot to a bright, sunny spot indoors near a lightly shaded south-facing window.
Transplant and Early Care
Grapefruit seedlings grow slowly, but they still need the right conditions and plenty of space to spread out as they mature.
Transplant all of the sprouted seedlings into individual 3- to 4-inch pots filled with sterile soilless growing medium once they produce several sets of leaves. Be sure to plant them at the same depth as they were in their starter pots. Use pots that have drainage holes.
Position the pots near a south- or west-facing window with roughly four hours of direct sunlight each day. Maintain temperatures between 60 and 70 F. In winter, temperatures must stay above 40 F.
Keep the soil evenly moist, but let the surface dry out between waterings to reduce the risk for root diseases. Water until the excess drains from the bottom of the pot.
Repot the grapefruit seedlings in spring into a pot that is no more than 1 to 2 inches larger than the previous pot. Use soilless medium and a pot that has multiple drainage holes around the base.
Move the pots outdoors to a sheltered area with bright, diffuse light in spring of their second year. Keep them watered as before, and feed every two weeks with 1/2 teaspoon of water-soluble, 10-10-10 fertilizer diluted in 1 gallon of water. If yellow leaves appear, reduce feeding frequency by half.
Transplant the grapefruit seedlings into half-barrel containers or into the ground in spring of their third year. Position them in a bright, sunny spot and fast drainage.