Giant Marrow A Step By Step Guide


Giant Marrow Growing Guide

Giant Marrow preparation starts during the winter months. I prepare the soil in readiness for growing these Giants. These plants grow large and depending on how many you wish to grow will determine the size of the area required. I typically grow four plants and use a space that is approx 35ft x 22ft or (10m x 6.7m). Soil needs to be free draining and the area ideally should be sheltered to prevent damage to the plants large leaves. Preparation starts in late September with the sowing of green manure.

Green manure germination in the giant marrow bed
Early start for green manure

I leave this to grow all through the winter. This does a few things which is quite important, but it is not a necessity to do. Green manure is brilliant as the types I use, Field Beans and Hairy Vetch are both known as Legumes.

  1. Legumes have the ability to take nitrogen from the air and store it in little capsules on their root system.
  2. The Green manure protects the soil during the winter months from being battered by the rain and cold, This prevents it compacting and destroying the structure of the soil.

3. By growing throughout the winter, you are providing a food source for all the soil web life, (Nematodes) and other bugs in the ground.

  1. Green manure when dug back into the ground adds organic matter.

This is good as these microbes help to break down animal manures and pathogens in the soil. It helps to release locked up fertilisers and so forth.

Full grown green manure
Green manure consisting field beans and hairy vetch

In early March,

We cut down the manure right to the ground. We leave all this growth on top of the ground for a few days to start breaking down.

green manure cut and left to rot down
Strimmed green manure

After about a week I dig in the Green manure into the soil by hand. This does not have to be a fine tilth as this comes later

double digging the giant marrow bed
Hand turning the giant marrow bed

The next stage to grow giant marrow

Is to get a soil sample. I use Lancrop laboratories to do my testing. You could just as easily do a basic test with a home kit. Once you get the results of your soil test, You can start to look at ways in which to adjust your soil for the optimum growing conditions for Giant Marrows. I add all amendments. Sometimes this might just need some more organic matter in which case I add a lot of manure. This manure MUST be well rotted if you’re adding it at this time of year. If your adding it in Autumn instead of green manure then it does not need to be well rotted.

Well rotted horse manure for giant marrows
Load of horse manure for giant marrow bed

Now that the soil is near enough ready we need to look at the plants themselves. With any Giant vegetable, it is all about the genetics of the seed. You need the right strain that has proven genetics to grow big. A normal marrow strain from a garden centre or online company can never reach these sorts of sizes.

Time to set giant marrow seed.

I set my seed to chit (which means to shoot) a little bit like you would potatoes, at the end of April. I do this by selecting the seed I want to use, Filling a small seed tray with vermiculite or compost and soaking it with lukewarm water. I then sit the seed on top of the soil and dust with some Mycorrhizal Fungi. Mycorrhizal fungiOpens in a new tab. are tiny, harmless critters that attach themselves to plant roots and actually help plants to make use of water and organic nutrients in the soil. They live on the roots of roughly 95% of all earth’s plant species.

Setting giant marrow seeds to chit
giant marrow seeds in a tray

This tray is now heated in a propagator to 21ºC (70ºF) and the seeds are allowed to chit. This takes around 7 to 10 days. They will then be ready to pot on into individual pots

Chitted giant marrow seed
The root system of a giant marrow seed

I dust these seeds again with Mycorrhizal FungiOpens in a new tab. and plant into small pots until they get going. We keep potting the marrows on into larger pots, each time dusting with Mycorrhizal Fungi.

young Giant marrow plant
First true leaf of giant marrow plant

The fungi do a fantastic job of enabling the marrows root system to build. This provides it the best start it could possibly have. Each step of its life must be as stress-free as possible. Should the plant get stressed at any stage it will not reach its full potential.

Root system of a giant marrow
The giant marrow root ball

It is now early May.

We turn our attention back to the ground in which the marrows will be planted out. We now rotovate this ground to a fine tilth. This incorporates all the feed and manure we have put onto the ground. By this stage, it has had time to break down.

Marrow bed finished after being rotovated
Rotovated marrow bed

We rake this bed flat. taking out any real large stones that have risen to the surface. I then place four old bed frames in situ, this is going to be where each plant is planted. You can, of course, fashion all sorts of structures, this blocks the wind until the plant gets established and later is used to keep the sun from ripening the marrow.

completed preparation of the giant marrow bed
finished giant marrow bed

After the last frost at the beginning of June. I plant out my Marrows. We want to get them out into the soil to start to acclimatise them.

settling giant marrows into their growing spot
Planting out giant marrow plants

When planting giant marrows,

The Marrow gets a fine dusting of Mycorrhizal Fungi and it’s then planted and watered in very well. We wrap the bed frames in fleece or plastic if there is going to be adverse weather.

Plastic wrapping to protect giant marrows
Wrapped Giant marrows to protect from the wind.

As the plant grows and starts to vine, you want to manoeuvre it to the direction you wish it to grow. We then stake the vine to the ground using cut off pieces of plastic coat hangers.

Giant marrow pegging
Pegging giant marrow vines

As the giant marrow plant gets bigger,

I bury the vines with soil, This helps the plant to anchor itself into the ground, and also allows it to put down extra roots at each leaf node. The more roots, the more the plant can take up water and nutrients. We continue to bury vines and I allowed the plants to reach 16ft in length and then stopped the tips growing by removing the tip. I also did this with all side shoots.

Giant marrows in ready made beds
Giant marrows starting to vine

The marrow plants then start to flower. We are looking for a flower to appear around 10-12ft away from the main roots and preferably on the main stem. Growing on side runners can still produce very large marrows. I have always tried to get them on the main stem as this is the main artery for the plant. Then should be able to produce more fluid and nutrients to the growing fruit. Once we locate a female flower in the right area we can hand pollinate it. The timing must be right. I pollinate mine around 48-50 days before the Malvern Autumn Show, which is where I hope to take a World Record one day.

The difference between Male and Female flowers can be shown by the female flower containing the fruit behind the bloom.

Differences between male and female giant marrow flowers
Male and Female Giant Marrow flowers

Giant marrow flower Prep

We cover or tie the female and male flowers up before they are due to open, this is to stop pollinating insects from cross-pollinating the flower. On the day they open, we take multiple male flowers and tear off all the petals leaving just the stamen section of the flower, we then use these and pollinate the female Pistil with the male stamen. 

pollinating Giant marrow flowers
male and female giant marrow flower

Once we have finished pollinating the flower we then tie the female flower back up again to stop cross-contamination.

tied giant marrow flower to prevent pollination
Female Giant Marrow flower

As the giant marrow forms

The flower will fall off and successful pollination will have occurred. All we need to do now is manage the plant for the next 48-50 days. To do this we need to feed regularly, I do this using Maxicrop seaweed feed, Comfrey tea and a sprinkling of Fishnure or 6x chicken pellets. It is important to remove any side shoots regularly and maintain the shape of the plant.

removal of side shoots
make compost from giant marrow cuttings

remove all flowers and unrequired marrows. I grow one marrow per plant.  Later in the year, I will allow a second to form. This helps prevent the marrow from splitting

giant marrow rejects
cutting off unwanted marrows

I donate all the removed marrows to old age complexes and homeless shelters. As well as keeping a few for use at home. Once a week it is prudent to spray your plants with an anti-fungal sprayOpens in a new tab. or whole milk watered down 10/1. This will help prevent powdery mildew forming. This disease can wipe out your leaves which are the solar panels of the plant. Without these, the marrow just will not grow. The next step as the marrow grows is to lift it out of the soil before it gets too big. You can use insulation foam board which will also insulate against a cold floor, or sand as I have used here. This will help prevent the fruit rotting.

protecting a giant marrow from rot
Giant Marrow sat on a sand bed

Giant marrow towards the end of summer

The plants get extremely big and take a huge amount of water. 30-40 litres of water will be required for each plant.

summer growth
Giant Marrows in the summer

Keep your marrow warm. Tucking it away on cold nights and covering it over in the daytime. This will prevent the sun from ripening it. If it gets ripe it will harden and split when taking on water.

Sat on a bed of sand to insulate from the ground
Giant Marrow wrapped in fleece

When it has finished growing the marrow just won’t grow any further.  It is important to check growth with a tape measure over the next few days to confirm it has stopped.

Giant Marrow taping
Taping the marrow to calculate weight

We should now be very close to show day. Do not cut the marrow unless you think it could split by a sudden downpour. Let up on watering at this point too. Try to leave the marrow on the plant as it will retain its weight. Cutting it early may cause it to lose some weight which could be all the difference on the show bench. If the marrow splits Its game over

Showing the split that stopped this one growing
Game over

One step closer to your giant marrow.

If you have managed to keep your marrows growing without splitting congratulations. You may now show it at your local show or one of the nationals. This is where the big boys play, such as Malvern.

Giant Marrow On The Show Bench
Showing At Malvern

So now you know what it takes to grow a giant marrow. It is a lot of work, but also a lot of fun and sometimes heartache. I hope this step by step growing guide will be of use to you. If you would like more information like this then why not visit us at our Youtube ChannelOpens in a new tab. or Facebook Page, just click the highlighted links. I would love to see you there and chat.  For now happy gardening I will speak to you soon 🙂

Giant marrows fully grown
Tony O’Neill with two giant marrows

© Copyright UK Here We Grow 2018

Tony O'Neill

I am Tony O'Neill, A full-time firefighter and long term gardener. I have spent most of my life gardening. From the age of 7 until the present day at 45. My goal is to use my love and knowledge of gardening to support you and to simplify the gardening process so you are more productive

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