Watermelon Rosario is one of the most popular varieties of watermelon to grow from seed. While they need warm growing conditions, Watermelon Rosario are capable of producing quite an impressive crop of home-grown watermelons even in temperate areas.
Having grown Watermelon Rosario myself for the last few years, yet found information on the internet lacking, I thought I’d spend some time talking about my experiences so you know what to expect.
Let’s start with probably the most important questions before we move on to some tips for growing Watermelon Rosario successfully…
Is Watermelon Rosario Easy to Grow?
Watermelon Rosario is surprisingly easy (and fun!) to grow if you either live in a warm area or have access to a greenhouse.
I’m based in the UK, which is known for reasonably cool summer weather and frequent overcast skies. Hardly the sort of the weather you’d expect to be conducive to watermelon growing. Despite that, Watermelon Rosario has flourished in my garden and has produced a host of fruits all with the minimum of effort.
I grow my Watermelon Rosario in an unheated greenhouse and they do very well indeed, taking up home in the sunniest area. While it takes some time for fruits to grow to ripeness, Watermelon Rosario is just a really fun plant to grow if you have a little spare space.
Personally I wouldn’t try growing Watermelon Rosario outdoors in the UK or northern areas of North America as the cooler temperatures are unlikely to yield the crop you’re seeking.
How Big Are Watermelon Rosario Fruits?
Unlike the giant watermelon fruits you see in the supermarket, Watermelon Rosario fruits are altogether smaller. Even under ideal growing conditions, Watermelon Rosario fruits tend to reach a diameter of 4-5” only.
While Watermelon Rosario fruits are quite modest in comparison to other watermelon varieties there are actually benefits to this. Firstly, it means that Watermelon Rosario can easily be grown up a support in your greenhouse, rather than clambering across the ground. This means Watermelon Rosario can be grown in quite a small section of your greenhouse.
Another benefit of the small fruits on Watermelon Rosario is that one melon represents just a couple of watermelon portions. No more taking up half the fridge with a traditional watermelon; these fruits can be harvested and eaten instantly, perhaps with a few leftovers taking up minimal space till the following day.
Lastly, if you’re new to growing melons then deciding on ripeness isn’t always easy. With the smaller fruits of Watermelon Rosario should you get it wrong, and harvest a fruit before it is properly ripe, it’s hardly the end of the world and there will be numerous other fruits still to come.
In brief I’d argue that the modest proportions of Watermelon Rosario fruits are actually a benefit rather than a weakness for those of us trying to grow watermelons at home.
How to Grow Watermelon Rosario from Seed
Watermelon Rosario seeds tend to germinate quickly and grow strongly so long as they’re given the right conditions. While we’ll talk about the ideal growing conditions shortly, possibly the most important factor when it comes to germinating Watermelon Rosario seeds is the provision of warmth.
A soil temperature of 20-25’C is recommended for germinating Watermelon Rosario seeds. Personally I use soil warming cables and heat mats placed indoors on a windowsill to facilitate this. Under these circumstances seeds pop up in a matter of weeks – sometimes even in days.
If you lack a heater or heated propagator then place the potted seeds into the warmest room of your home, ideally on a sunny windowsill.
In all but the warmest areas it’s probably best not to plant Watermelon Rosario seeds in your greenhouse initially, due to the low night-time temperatures experienced by unheated greenhouses in early spring. Instead, plant in your home and aim to plant out in your greenhouse as spring really gets underway.
When to Plant Watermelon Rosario Seeds
In temperate climates watermelons need as long a season as possible to produce fruits. Watermelon Rosario is best planted very early in the season, with March being an ideal month. This gives the seeds a couple of months to germinate and grow on before being planted out in their final position around May.
That said, I have started Watermelon Rosario seeds later in the season – as late as the end of April – and have still ended up with ripe fruits to enjoy.
All the same, the sooner you plant your Watermelon Rosario seeds in the year, the better the harvest you’re likely to enjoy.
Let’s discuss some basic tips for getting your Watermelon Rosario seeds germinating and growing strongly to start you off on the best possible footing.
One Seed Per Pot
Watermelon Rosario grows big, and does so quickly. Therefore chucking the Watermelon Rosario seeds you’ve brought into a single pot can create problems quite quickly when they germinate. In my opinion it is a lot easier to plant one seed per pot.
While I appreciate that not every seed will germinate, those that *do* germinate become easier to manage when potted individually. Your Watermelon Rosario seedlings will quickly start putting out tendrils, trying to grab onto anything possible. This means that Watermelon Rosario seedlings can quickly become intertwined, leading to difficulties with separating them before planting.
By planting Watermelon Rosario seeds individually it’s easy to keep the seedlings apart from one another so they don’t attach to one another.
Generous Pot Size
Watermelon Rosario has a most impressive growth rate. Within a matter of weeks that tiny fragile-looking seedling poking through the surface of the compost will quickly take on a life of its own. You can almost see them growing in good weather. This means that any Watermelon Rosario seedling will quickly take over smaller plant pots, and may become pot-bound quite quickly.
This speed of growth means that I recommend planting Watermelon Rosario seeds in quite generous containers of 4-5” in diameter. This provides a reasonable amount of growing space before your plants need to be potted up. By this point they should be vigorous and healthy, easily able to withstand the repotting process.
Like many fast-growing greenhouse crops, Watermelon Rosario needs a lot of nutrients if it is to reach its potential. Don’t scrimp on the compost, therefore. A rich compost, with plenty of organic matter, tends to work well. Personally I use a peat-free multipurpose compost for seedlings, and even then I add liquid fertilizer during the fruiting season.
Plant your Watermelon Rosario seeds at a depth of 1-2cm, ideally leaving a few centimeters between the top of the compost and the top of the pot. This makes covering the pot a little later on much easier.
Water Heavily & Allow to Drain
Water your pots of Watermelon Rosario seeds well, then allow them to drain properly. Probably the easiest option is to simply place your Watermelon Rosario into a tray of water for an hour or so. The compost will soak up lots of water, without the seeds themselves getting disturbed.
Then remove the pots from the tray and leave them so excess water drips away.
Cover Pot to Retain Moisture
Placing the pot into an enclosed environment can help to retain the all-important moisture. Affix plastic over the top of the pot or even better place the whole pot into a clear plastic bag or a propagator.
Keep an eye on your Watermelon Rosario seeds and add extra water as necessary. Your goal should be to keep the compost moist (not not soaking) at all times.
Keep Seeds Warm
As stated earlier, Watermelon Rosario seeds need to be kept warm to germinate properly. This means they shouldn’t be planted in an unheated greenhouse or outside. Instead, they must be cared for indoors for the first few weeks or months, until the last frosts have finally finished.
Pop them into a warm airing cupboard or use a soil warmer to provide temperatures of 20-25’C.
Even after germination aim to keep your seedlings away from cold or draughts.
Growing on Watermelon Rosario Seeds
Once the cold winter weather has gone away, and any frosts are a distant memory, Watermelon Rosario can be planted into its final growing position. Here in the UK that means planting Watermelon Rosario in my unheated greenhouse around April or May.
Personally I normally grow Watermelon Rosario in growbags just like tomatoes, but they can also be grown in containers or popped straight into greenhouse beds.
If you want the healthiest watermelon plants and the most fruits possible then it makes sense to regularly feed them.
I use a tomato fertilizer, provided every 2 weeks during the fruiting season. I simply prepare it as per the bottle instructions for tomatoes and it seems to work well.
Of course, other options can also work well, including granular fertilizer or even comfrey fertilizer.
Until you cut into your very first Watermelon Rosario fruit you don’t realize what an incredible job your watermelon plants do of absorbing moisture from the soil and pushing it into the rich, juicy fruits. Just consider how much water is really in a fruit that is 4-5” across, then furthermore think that a single plant may produce multiple fruits.
It should come as little surprise, therefore, that you should aim to water your Watermelon Rosario plants generously throughout the season. In hot weather it may become necessary to water your plants twice or even three times a day. Don’t worry, though – your watering efforts will soon be rewarded with the most amazing crop of home-grown watermelons
Provide Strong Support
Some gardeners opt to grow watermelons across the ground, letting their plants ramble horizontally. However if you’re not careful even a modest plant like Watermelon Rosario can really take over your available growing space.
A better option, in my opinion, is to grow Watermelon Rosario up a sturdy support. This saves growing space for other plants, but also has other benefits. It keeps the fruits off the ground, thus preventing them from rotting if they get damp. It allows you to harvest your fruits without too much bending. And of course it allows proper air flow, reducing the chances of pests and diseases taking hold.
While the fruits of Watermelon Rosario are relatively small by watermelon standards, a plant laden with 3 or 4 fruits is still pretty weighty. When you grow a number of plants together, as I do, the weight can really start to add up.
Personally I build a frame out of sturdy garden canes, attaching them to one another with cable ties. This provides all the support necessary. The watermelon plants themselves can then be gently trained onto the frame, and gently tied into position with garden twine to prevent them falling over.
Harvesting Watermelon Rosario Fruits
Watermelon Rosario fruits are ready to harvest at the height of summer. July to September seems about right based on my own experiences. They can simply be snipped gently off the plant using a pair of secateurs, with the remaining fruits allowed to grow on.
Figuring out when a melon is ripe to pick is no easy feat and in truth takes a little bit of trial-and-error combined with experience. There are, however, a few useful tips I can give to help you decide if your Watermelon Rosario are ready for picking:
Tap and Listen
One proven way to assess the ripeness of any melon is to hold your ear closeby and tap it with a finger. A ripe fruit will sound almost “hollow”.
Trust Your Nose
As the watermelons ripen, so you’ll start to enjoy the delicious smell of watermelon permeating from your greenhouse. It is perhaps most noticeable when you open your greenhouse doors in the morning. A strong watermelon scent is a very good sign that one or more fruits are ready for harvesting.
Try moving from one fruit to the next, sniffing deeply. The ripest fruits should have the most pungent aroma.
Lack of Growth
Watermelon Rosario produces quite modestly-sized fruits. These will reach a maximum size of some 4-5” in diameter in my experience, then will not grow any larger. If you have one or more fruits that seem to have stopped growing in diameter despite ideal growing conditions then this is a very good sign that they may be ready to harvest.
Change in Surface Color/Texture
Lastly, and possibly most reliably of all, it seems that Watermelon Rosario changes its appearance when the fruits are ready for picking. When growing strongly the fruits have a glossy, shiny, almost-waxy appearance to the skin. When ripe, however, the fruit turns a more “matt” effect on the surface and generally looks a bit duller.
Downsides to Growing Watermelon Rosario
Watermelon Rosario is generally quite an easy plant to grow in an unheated greenhouse, however it is not without its downsides.
I have two concerns when it comes to growing Watermelon Rosario that are worth sharing.
Firstly, the watermelon fruits themselves contain an awful lot of seeds. This can make actually eating your crop rather frustrating as you seem to spend longer eating round the seeds (or spitting them out) than you do really savouring the incredible flavour. While this isn’t a deal-breaker for many people, it is an annoyance all the same that can add to your preparation time.
The second issue with Watermelon Rosario, though this is not confined to just this variety, is that the big green leaves can be very tempting for a variety of pests. Last year I fought a season-long battle with red spider mites for example. While ultimately we prevailed and ended up with a decent crop, it’s something to be mindful of.
The important thing when growing anything in your greenhouse, but especially more fleshy plants like Watermelon Rosario, is to keep a regular eye on them for any signs of parasites or pests, and take appropriate action as quickly as possible. Once an infestation really sets in it becomes a whole lot harder to solve.