A few things keep radishes and other root crops that form bulbs
1 Too much nitrogen will give you lush top growth at the expense of roots. Use a low nitrogen fertilzer.
2 Spacing. You need to thin plants to their mature spacing. A radish is about an inch to an inch and a half so you need to give them that much space for the bulbs to grow. Two inches would probably be better, 4 inches for beets and turnips.
3. Acidic soil. Acidic soil makes micronutrients more available and more nitrogen available but less calcium and phosphorus.
Roots do better in more neutral to slightly alkaline conditions.
4. They really like bone meal
Try this. If you have not gotten a soil test it really helps. A soil test will actually tell you what your conditions are and guide you to your best plant choices and how to optimize pH and nutrients for what you want to plant.
In a pot with MG potting soil plant your radishes. You don't need a very deep pot a wine box 4-6 inches deep is all you need.
If you can get garden tone and bone meal mix 2 parts garden tone with one part bone meal.
Plant the radishes 2 inches apart to the depth on the back of the package. I plant 1/4-1/2 inch deep. Keep soil moist. until they germinate. It should take less than a week. When you get true leaves. side dress with the garden tone and bone meal.
Keep soil evenly moist.
When the bulbs form they will push themselves out of the ground 1/3 will be below and the rest will be above. Radishes are ready in about 21-30 days depending on the weather.
This will work with beets too.
My community garden is alkaline with a pH of 7.7 so beets do better there than in my home garden with a pH of 6.0. In my home garden I get lots of leaves and the only beet that grew a bulb to any size was the one that grew in the pathway outside of the garden. I have way too much residual nitrogen in my home garden.
Most potting soils have had dolomite lime added to it so they are about pH 6.5 and they have some starter fertilizer so you could actually skip the side dressing if you want to. Do not use moisture control unless you live where it never rains,.
Happy gardening in Hawaii. Gardens are where people grow.