Radishes are a rapidly maturing cool weather crop. They are among the easiest vegetables to grow - either in soil or hydroponically.
There are a few basic practices that should be adhered to and some simple tips to ensure an abundant and continuous flow of radishes.
Nutrient pH for Hydroponic Radishes should be 6.0 to 7.0
Temperature should be kept between 50 and 65 degrees Farenheit. Longer radish varieties tolerate heat better than the short round types.
8 - 10 hours of light daily optimal - but a bare minimum of 6 hrs.
Radishes are best started from seed. Transplants are generally not recommended.
PPM 840 - 1540 EC 1.6 - 2.2
Harvest 12 months/year is possible with staggered growth cycles.
With most radish varieties both the radish roots and greens are edible.
Radish seeds will germinate within the week, usually just a few days and you should be harvesting radishes in 3 - 4 weeks.
I prefer to start my Radishes in grow cubes which eliminates the need to thin them out later. They can also be scattered directly into the growing media. Up to about 100 seeds per larger tubs- 20 - 30 for 5 gallon buckets, smaller setups- use your judgement, your primary consideration should be spacing at this point.
Radish seeds need proper spacing to produce healthy radishes which are the primary edible part of the plant.
Spacing affects the growth and mature size of the radish root. The radish greens, the leafy tops, don't require much space, but the roots do.
Try to leave 1/2" minimum but optimally 3/4" spacing between plants. Larger winter varieties need slightly more space - consult the seed pack as this varies ever so slightly.
Maintainence and Propagation of Hydroponic Radishes
Radishes should be started on a basic Grow nutrient to encourage the growth of the green tops, once the tops are sufficiently developed - usually by the beginning of the second week, switch to a root nutrient. If you stay with the grow nutrient you will end up with lush greens and scrawny under-developed radish roots.
To stabilize your plants, a growing media to support and stabilize the seedlings is needed. Sand or sphagnum moss will suffice.
A blend of perlite, vermiculite will work even better. A little peat blended in is not a bad idea - but not absolutely necessary. If using net pots seal it with a coffee filter, or tissue paper first. Related Article : Growth Mediums
Be sure to leave some head space, at least an inch, more if possible, between the filler from your reservoir and the containers top.
Radishes need a bare minimum of 6 hours of light daily, 8 - 10 is best under most conditions. In nature they tolerate partial shade. In a hydroponic setup less light than many other crops will suffice. Too much light generates too much heat and radish plants do not develop radishes in higher than normal temperatures. See - Grow Lights
Temperature and Humidity
They thrive in cool temperatures, best daytime temperatures between 72F and 76F.
Nighttime temperatures should be around 60 degrees Farenheit. They can tolerate and adapt to temperature fluctuations and are not fragile in this respect.
If you are not seed saving, then don't even worry about pollinating your radishes. They will still produce the greens and radish root. IF you want or need to pollinate your plants - Go for it . Hand pollination can be such a bother - it is time consuming and labor intensive. See Indoor Pollination
Trouble Shooting Hydroponic Radishes
Radish has a tendency to bolt to seed if not kept moist enough - when this occurs they are useless, other than for seed saving.
If they are kept constantly and persistently soaked, rot becomes an issue - which is a serious issue in hydroponic setups. When the radish roots approach maturity consider funneling your water below the medium, deeper than the radish itself. The radish plant should still be able to draw adequate moisture and nutrients via transpirational pull for short periods. Alternating from funneling to your normal modus operandi should also be considered if rot is an issue, or you fear it may become one.
Longer radish varieties occasionally develop a black root that produces dark blemishes and occasionally rots at the base of the roots. If this is a persistent problem it is advisable to grow only round radishes.
Avoiding Root Rot
1. If transplanting from soil to a hydroponic system be sure to remove all soil residue off the root-ball without saturating the roots. Try not to let the roots dry out in the hardening and transplanting process. The plants energy is stored in the root system so be sure to do as little damage as feasible when transplanting.
2. Hydroponic Root Health supplements will help to eradicate Root rot , so will horticultural peroxide. The least expensive route is common household bleach. Add 5 - 7 drops per Gallon of water twice weekly. Chlorine will naturally dissipate in water so it should be added every 3 -4 days or 'twice weekly'.
If you prefer to stick with an organic method Beneficial microbes / Beneficial bacteria have been reported to be successful. Most commonly Mycorrhizae , which are beneficial fungi that penetrate the root systems of most plants in nature. They are helpful in providing improved uptake of water and nutrients from the growing media. They also help protect the roots from harmful pathogens and disease.
Trichoderma is a beneficial fungus that colonizes root systems. They prevent harmful fungi from entering the same root system, stimulate root development, and improve the plant's adaptability to environmental stress.