Tag: gardening

Where Do Seedless Watermelons Come From?

One of my first Seedless Watermelon Trials, Comanche County Texas

I have been asked on numerous occasions “Where Do Seedless Watermelons Come From?” or “How do you get seed from a seedless watermelon?” Well, the process is simple but lengthy, taking two generations but the end result is fantastic.

First, you need to understand a little about chromosomes, the threadlike bodies that contain genes for development. A regular watermelon has two sets of chromosomes and is called a diploid (di for two). A plant breeder will take a diploid watermelon seed and treat it with a chemical called colchicine. Colchicine will cause the seed to develop a melon with four sets of chromosomes called a tetraploid (tetra for four). This melon is grown out and the seed harvested for the next growing season. This tetraploid seed is planted and begins to grow but the plant is covered with a spun row cover to prevent any pollination so that the plant breeder can pollinate at the right time with a diploid melon variety. These melons will grow and the seed from them will be harvested. The cross of tetraploid plant with a diploid plant result in triploid seed. This plant has three sets of chromosomes and is the “mule” of the watermelon family. This seed when planted will produce a seedless melon meaning it is sterile. You may see some sort of seed like “carcass” but that is soft and not developed shown in the picture below. They don’t affect the taste or the quality.

Seedless melons are really a favorite of the urban clientele. They don’t buy grapes with seeds, and they don’t like melons with seeds (what do you do with the seeds in a nice restaurant). They are excellent for salad bars and are sold in grocery stores sliced and ready to eat. Seedless watermelons are typically smaller and so fit easily in the refrigerator, another plus for the urban American. One of the first and most popular seedless varieties was Tri-X 313. I was told that the Tri-X meant triploid, the first 3 was 3 months maturity and the 13 was the typical weight of 13 pounds per melon. Sounds good anyway!

Organic Seedless Melons – Florida Fields to Forks

Growing seedless melons are a little different than the typical watermelon. First this seed is very fragile and must be germinated under higher-than-normal germination temperatures. We will germinate seeds in chambers with 90+ degree temperatures. This forces the seed to quickly germinate and begin to grow versus a cold soil in the field which will slow seed germination enough that most seedless plants won’t make it. Because of its temperamental nature a seedless watermelon is grown as a transplant first and then moved into the field later after getting a good root system established. These seeds cost from 17¢ to 50¢ a piece and growing the actual plant in a pot to be transplanted costs another 15¢ for a total of approximately 50¢ per plant. The germination percentage is low for seedless, around 80%, so that cost can go up even more. It takes about 1500 to 1700 plants per acre or about $600.00 per acre of planted seedless melons, a lot of money and still 80 days till harvest.

Seedless has other good traits besides being seedless. They are very productive, generally producing more melons than any other hybrid if grown properly. They are also disease tolerant plants resisting many of the diseases that other melons quickly die from and seedless are good shippers, holding flavor for a long time.

I mentioned that the seedless is the “mule” of melons, well a watermelon produces both male and female flowers so that we can plant one variety in a field and bees can pollinate with no trouble. A seedless melon produces a male flower that cannot pollinate another melon so to get by this we have to plant seeded variety melons in rows next to the seedless rows to insure good pollination. I have seen mix-ups in the field where seedless plants covered 10 solid rows so that the outside two rows were the only ones with melons. Having a pollinator row for seedless is mandatory if you want seedless melons, a fact you should know if you want to try growing seedless melons.

Is a seedless melon organic?  Absolutely. Colchicine is a naturally occurring alkaloid compound found in certain plant species, primarily the Colchicum autumnale plant, also known as autumn crocus or meadow saffron. Colchicum autumnale is native to Europe and Asia. The alkaloid colchicine is extracted from the seeds, corms (underground storage organs), and other parts of this plant. It can be applied to the seeds or plants, and this causes the doubling of the chromosomes. This process seems unnatural but in nature it is not that rare to find naturally occurring tetraploid melons!

Colchicine has been used for centuries in traditional medicine, particularly in the treatment of gout and certain inflammatory conditions. However, it is important to note that colchicine can be toxic in high doses, so it should only be used under medical supervision. In organic production the melons should be treated with the naturally derived colchicine not the synthetic. As always, check with your CERTIFIER first!

Melon Fertilizer Scheduling – Even in Organic Production

There are all kinds of ways and amounts to fertilize melons and each of you has their own “special mix” that works just right for you.  Even though each producer does it differently there is some interesting information about amounts based on growth that might be useful.  Dr. Don Maynard, University of Florida edited the Watermelon Production Guide for Florida for years and in it he listed a fertigation schedule for a seeded and plastic mulched watermelon crop.  I am asked occasionally how much nitrogen I should be applying, and the answer is “it depends.” I use the number 120#’s as the total N that you will probably apply in the season minus what you’ve already put out, say 40#’s which leaves 80#’s to apply in 8 weeks or 10#’s per week.  This is simple, but it doesn’t consider that sometimes the plants need more nitrogen than at other times.  Dr. Maynard includes this schedule which considers the plant’s needs. 

This chart assumes that you will apply 120#’s of total N and that 20% or 24 lbs. of N was already put down as a starter N before planting.  Assuming it takes 15 weeks from planting a seed to final harvest then you just follow along with each week applying the amount of N recommended per day for seven days then go to the next week.  They recommend applying N through the drip each day but not many producers do that so just use the chart to calculate how much N you need and when you need it.  He also adds that if you are using transplants then start on week 3 just shortly after you set out the plants.

 So, what this means is that by week 8 you should have applied 28% of the fertilizer plus the 20% you put down as starter or 48% of the 120#’s.  In week 8 you would apply 1.4 lbs. of N per acre per day or 14#’s of liquid 10% (1 gallon is 10.5 lbs.) per acre per day or 98#’s per week which is about 9.33 gallons per week per acre of liquid 10%.  Just remember that we are talking pounds of actual nitrogen, but no nitrogen source is pure but is a percentage. Divide the pounds of N needed by the percentage to get amount of fertilizer to apply.  1.4/0.10 = 14#’s. Now an acre is a physical planted acre with plants having about 24 square feet per plant. Reminder: in organic you may want to adjust the schedule earlier, but the principal is that melons need lots of N right before and just after they start sizing melons.

You can see that in weeks 9 and 10 the plants are really using nitrogen and after that the plants begin to concentrate on making fruit instead of plant growth, so nitrogen is used less.  Those big plants also have stored nitrogen in the leaves which they can use for maintenance and fruit giving you a safety net.  We see the same kind of response in most field crops like corn where we would put most of the nitrogen out before tasseling to insure it is available when the ears are made. 

How do you do a fertilizing schedule like this in Organic Production? There are several companies that make fertilizers approved for organic production that can supply lots of somewhat readily available nitrogen.  As an example, Nature Safe has a pelleted 11-1-0 for organic production and Ferticell has Active 13-2-2,  Ferticell has an Explorer Liquid 10-0-0 and an Explorer 16-0-0.  I am sure there are many other companies that sell products like these that will add to your fertilizer needs beyond what you get from using high quality compost.

Always check your soil and your compost for nutrient content before you buy and apply these high nitrogen organic fertilizers. As always, I do recommend you check with your certifier before adding any amendments or soil fertilizers.