• Dom@UrbanVeggieCrew.com.au

How to Grow Tomatoes in a Wicking Bed

Updated: Mar 27

Anyone will tell you that home grown tomatoes taste completely different to store bought varieties. There's nothing more satisfying than picking your own fresh, juicy tomatoes and serving straight from garden to plate. There are many vegetables that grow better in wicking planters - let's take a look at tomatoes to see if they go well with the constant watering a wicking bed provides.

Tomatoes Grown in a Wicking Bed
Tomatoes Grown in a Wicking Bed

Tomatoes can grow fantastically well in a wicking bed provided the bed follows a few basic principles. The depth of the wicking layer needs to be sufficient to ensure the roots are not constantly in water. There needs to be good overflow drainage and preferably an air gap. The dry surface of a wicking bed helps reduce diseases bought on from humidity and top watering.


Tomatoes fruit much better when they have a constant water supply, and a wicking bed provides this. Fruit deprived of water at certain points in the lifecycle is prone to cracking when water then appears later. Making sure tomatoes have an optimal amount of water is extremely tricky when watering from above. A well constructed wicking bed takes away the guess work and provides the correct amount of water through the entire lifecycle of the plant.



Preparing Wicking Beds for Tomatoes

The wicking bed should be constructed correctly to have success with tomatoes. Bearing in mind the following points when you set up your wicking bed will help ensure great success with tomatoes


How Deep Should Wicking Bed Soil Be for Tomatoes?

Tomato roots prefer not to be constantly in contact with completely saturated soil. Good deep roots are important, so how deep should a wicking bed be?


Tomatoes in a wicking bed require at least 10 inches (25cm) of soil, but the deeper the better. Water only wicks up around 30-40 cm, so the more depth you can provide in your wicking bed for your tomatoes, the better. A 35cm soil layer and 5cm mulch layer above that is ideal.

We like to over-fill our wicking beds above the level at which water wicks. This has a few advantages:

  1. The tomatoes can be planted in a trench and backfilled once they are growing to provide a better root system

  2. The surface remains drier with less evaporation and even less fungal disease

  3. Soil typically settles in a new wicking bed - overfilling allows for this to an extent and ensure the tomatoes have an adequate root depth

How To Prepare the Soil in a Wicking Bed for Tomatoes

Tomato stems contain many small hairs. These can root when beneath the surface, so the more soil you can pile up around the stem, the stronger root system you can develop. If you start with the wicking bed over-filled by 4 inches (10cm), then plant in a trench 4 inches deep, when you remove the bottom set of leaves, you can backfill the trench and give the plant an extra 4 inches of rooting stem.

This means extra nutrition exchange is possible, leading to better yields.


For tomatoes to thrive, the potting mix in a wicking bed bed should be well rested ideally, and heavily mulched . Lots of organic material should be mixed in; well composted manures, worm castings, or whatever you have to hand. Early in the lifecycle the plant will be nitrogen hungry. But avoid too many slow release nitrogen sources as at the fruiting stage you will want to focus on potassium for fruit rather than prolific leaf growth


A soil pH of 6.5-6.7 is ideal - there are many low cost pH meters available to measure this - it is well worth doing if you can get one.


Should You Mulch Tomatoes In a Wicking Bed?

Tomatoes are self pollinating, and whilst that is useful, it does makes them very prone to many diseases, the most common being of a fungal nature.

Many people familiar with growing tomatoes will remove the bottom leaves before they get diseased. This is often because fungal spores present in the soil are splashed up onto the leaves during watering or rainfall.


You should definitely mulch tomatoes in a wicking bed. This prevents rainfall from splashing the lower leaves. It also raises the surface level which helps ensure the surface stays dry. This lowers the humidity between the plants - another cause of fungal disease. In addition, a good organic mulch will feed the soil biome and provide future nutrients.


Sowing and Planting Tomatoes in a Wicking Planter

The method for sowing tomatoes in a sub irrigated planter in not really any different to any other type of raised bed. But do note the comments above about planting in a trench to give a stronger root system

Tomato sown in a wicking planter
Tomato sown in a wicking planter

Can I Plant Tomato Seeds from Last Year?

You can usually plant any tomato seeds. However non-heirloom varieties may not produce the same type of tomato they come from, and revert to type.


Seed can be confidently sown the following year if they are taken from heirloom seeds. If you select an heirloom variety you can confidently dry out a handful of seeds to sow the following year.


What Soil Temperature do Tomatoes Need in a Wicking Bed?

Potting mix in a wicking bed for Tomatoes
Potting mix in a wicking bed for Tomatoes

Tomato seeds are literarily desperate to germinate! Anyone that has put down immature compost will testify to this!


Cooler soil causes slower germination in tomatoes than warm soil. Ideal temperatures are 20-27 Celsius (70-80F). Seeds at lower temperatures will still germinate well, but will require longer, up to a fortnight in some cases.


That said, paradoxically, cooler soil is preferred for encouraging early growth of foliage although too cool can stunt growth. So things works quite well where the sun is warming the upper layer of soil where the seed is, with the lower layers slightly cooler


For fruiting, anywhere between 15 and 30 Celsius works well (60-88F) . Tomatoes love the heat to an extent; for those really hot days, the constant evaporation from wicking beds proves invaluable to moderate the temperature somewhat. And the continuous supply of water assists here.


What is the Recommended Spacing for Tomatoes in a Wicking Bed?

This depends on whether the tomatoes are determinate or indeterminate, and if the latter it also depends on your pruning approach. Lots of gardeners like to prune to two or three main stems per plant. This will need wide enough spacing to accommodate staking of all three stems.

However we prefer an approach of growing a single stem per plant, so can plant a lot closer.


The ideal spacing for Indeterminate tomatoes grown on a single stem is around 25cm (10 inches). A double stem requires more space, around 50cm (20 inches). Determinate tomatoes should be planted around 12 inches or more apart to ensure good airflow around the leaves..


A great way to Stake Tomatoes in a Wicking Bed

Tomatoes are one of those plants that need support. We have cultivated them to grow fruit larger than their stems can support.

Staking tomatoes in a wicking bed should be done with care so as not to disrupt or perforate the liner, or any geo-textile that is protecting the wicking layer. We recommend fixing posts to the side of the bed, ensuring no fixing pierce the liner. Then run a cross member up high and drop strings from it to each plant.


This method and an accompanying pruning strategy is described in good detail in the video opposite. The hidden advantage of stringing up tomatoes requires an understanding of how a tomato plant behaves naturally without human intervention.


Tomatoes are vines. hey want to wander. A tomato's natural inclination is to meander over a large area putting down new roots from it's stem wherever it can. This is why it's stem can put down roots from any point, and why it continually branches out new stems. That way, if one part of the plant gets disease, another area a few feet away is self sufficient and lives on.


Using the string method described in the video above, and extra string length can be left where the top is tied off. Now if this is high enough, by the time the plant reaches the top of the string, the bottom leaves have been pruned, and the bottom fruit is ready for picking. Once that bottom set of fruit is well on it's way , you can simply let out more string, and lower the whole plant. Let the lower stem coil on the ground, and cover it over with mulch or soil. The lower stem will then put down roots.


Repeat this process as the fruit and leaves are removed further up the stem, and the plant will live on, getting longer and longer until it gets diseased or the climate goes out of it's productive range.


This method has three advantages:

  • More roots means more nutrients get into the plant, which means better, more prolific fruit

  • The nutrients continually enter the plant further up the stem and closer to the fruit

  • You end up getting the fruit yields of trellis many times higher than you actually created if you can keep the plant alive!

This is why we recommend to prune to a single stem. The yields with this method are far superior.

Do I need to Water Tomatoes in a Wicking Bed?

Since wicking beds water from below, the tomatoes will be well hydrated throughout their lifecycle. But we recommend a wicking bed to be over-filled above wicking level to give a dry surface in order to deter weeds, pests and disease. This is especially important for crops like tomatoes which are very prone to fungal diseases.

It is recommended that tomato seeds are watered when first planted in a wicking bed, and kept moist until germination occurs, One great way to do this in a wicking planter is place a plank over each row of newly planted seeds after initial watering to stop the soil drying out, and keep the temperature more constant between day and night, assisting germination. Then simply check under the plank each day until you see the germinated seedling then remove the plank. At this point, the wicking bed will provide sufficient water below the surface to the roots that will have developed.


Seeds will germinate in under a week in most cases. If excess seeds were planted, they can now be pricked out to give the spacing required. Once the tomato has three sets of leaves, remove the bottom set and backfill the trench they are planted in with the soil that was set aside. Pat it down well to give good support to the plant


Tomato Pollination in a Raised Garden Bed

Tomatoes are self-pollinating; that is they don't need another plant to cross pollinate with. They usually pollinate well on their own from insect and wind vibration. However some folks like to give them a helping hand using the back of an electric toothbrush behind the flower to vibrate and dislodge the pollen, simulating insect activity.

Companion Planting Tomatoes in Wicking Beds

We have had success companion planting with Basil - a match made in heaven as any Italian will tell you. But what else grows well with Tomato in a wicking planter?


The following vegetables and herbs can be safely companion planted with tomatoes: basil, carrots, celery, asparagus, chives, parsley, parsnips, onions, marigold. It is best to avoid rosemary, dill, potatoes, fennel and strawberries


Wicking Beds are Ideal for Tomatoes!

The combination of a good constant water supply, and low nutrition runoff that a wicking bed provides makes them great for growing Tomatoes. If you follow the pruning and string-staking method described above you will be amazed at the crops that can be produced in a wicking bed!

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